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Zero-energy states in graphene M. E. Portnoi, C. A. Downing, R. R. Hartmann, N. J. Robinson and D. A. Stone School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK M.E.Portnoi@exeter.ac.uk

Abstract There is a widespread belief that electrostatic confinement of graphene charge carriers, which resemble massless Dirac fermions, is impossible as a result of the Klein paradox. We show that full confinement is indeed possible for zero-energy states in pristine graphene. We present exact analytical solutions for the zero-energy modes of two-dimensional massless Dirac fermions confined within a smooth one-dimensional potential given by hyperbolic secant [1], which provides a reasonable fit for the potential profiles of existing top-gated graphene structures [2-5]. A simple relationship between the characteristic strength and the number of confined modes within this model potential is found. A numerical method for finding the number of fully confined zero-energy modes in any smooth potential, decaying at large distances faster than the Coulomb potential, has also been developed and used to evaluate the conductivity of a channel formed by a realistic top-gate potential [6]. The long-range behaviour of the potential defines the threshold condition for confinement, with power-decaying potentials demonstrating drastically different behaviour from exponentially-decaying and square well models. An experimental setup is proposed for the observation of fully-confined electronic guided modes (see Fig. 1). We also show that full confinement is possible for zero-energy states in electrostatically-defined quantum dots and rings with smooth potential profiles. The necessary condition for confinement for potentials decaying faster than an unscreened Coulomb potential is a non-zero value of angular momentum, i.e. the confined states are vortices (see Fig. 2). Again, analytic solutions are found for a class of model potentials [7]. These exact solutions allow us to draw conclusions on general requirements for the potential to support fully confined states, including a critical value of the potential strength and spatial extent. The implications of fully-confined zero-energy states for STM measurements and minimal conductivity in graphene are discussed. We demonstrate that the excitonic insulator gap predicted some time ago [8] and revisited recently by several groups [9,10] cannot exist in graphene samples with back gates as confirmed by experiments [11]. A qualitatively different picture based on Bose-Einstein condensation of zero-energy electronhole vortices (excitons) is proposed to explain the Fermi velocity renormalization in gated graphene structures which is observed instead of the gap.

References [1] R. R. Hartmann, N. J. Robinson, and M. E. Portnoi, Phys. Rev. B 81, 245431 (2010). [2] R. V. Gorbachev et al., Nano Lett. 8, 1995 (2008). [3] G. Liu et al., Appl. Phys. Lett. 92, 203103 (2008). [4] A. F. Young and P. Kim, Nat. Phys. 5, 222 (2009). [5] J. R. Williams et al., Nature Nanotechnology 6, 222 (2011). [6] D. A. Stone, C. A. Downing, and M. E. Portnoi, Phys. Rev. B 86, 075464 (2012). [7] C. A. Downing, D. A. Stone, and M. E. Portnoi, Phys. Rev. B 84, 155437 (2011). [8] D. V. Khveshchenko, Phys. Rev. Lett. 87, 246802 (2001). [9] J. E. Drut and T. A. Lähde, Phys. Rev. Lett. 102, 026802 (2009). [10] T. Stroucken, J. H. GrÜnqvist, and S. W. Koch, Phys. Rev. B 84, 205445 (2011). [11] D. C. Elias et al., Nature Physics 7, 201 (2011).


Figures

Fig 1. (a) A schematic of a gedanken experiment for the observation of localized modes in graphene waveguides created by a top-gate. (b) The electrostatic potential created by the applied top-gate voltage is modeled as a hyperbolic secant. The plane shows the Fermi-level position.

Fig 2. (a) Radial wave-function components for the first two states with angular momentum m = 1 for the Lorentzian potential (a) N = 0; (b) N = 1; and for a model ring-like potential (c) N = 0; and (d) N = 1. Here N is the number of non-zero nodes in the wavefunction component, which has the smallest number of nodes. Solid (dotted) lines correspond to the upper (lower) wavefunction components. Insets: shape of the probability density for each state. lines correspond to components χA (iχB). Insets: shape of the probability density for each state.


Graphene on Pt step edges 1

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P. Pou , L. Rodrigo , R. Pérez , P. Merino , A. L. Pinardi , J. Méndez , M. F. López , J. A. Martín-Gago

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Dpto. de Física Teórica de la Materia Condensada, Univ. Autónoma de Madrid, Spain 2 Instituto de Ciencias de Materiales de Madrid, CSIC, Spain pablo.pou@uam.es

Understanding the coupling of graphene with its local environment is critical to integrate it in tomorrow's electronic devices. Previous studies have shown that highly perfect sheets of graphene can be obtained by epitaxial growth on metal surfaces, and for some transition elements, like Cu or Pt, the interaction is very weak and many characteristic properties of graphene are preserved [1,2]. In this work, we show the structure of graphene grown on Pt close to the steps where the flakes start to nucleate. To this end, we combine scanning tunneling microscopy (STM) experiments with density functional theory calculations (DFT) and non-equilibrium Green's functions (NEGF) methods to model the electronic transport. RT-STM experiments on Pt have succeeded in mapping the structure of a graphene flake on a Pt steps edge showing atomic resolution not only on both the graphene and the metal but also on the boundary (see figure). By combining them with our ab initio simulations [3], we have been able to understand the competition between the interaction of graphene with the step and with the Pt surface that controls the structure and chirality of the flake edge and the observed Moiré structures. We have determined both the atomic and electronic structures of graphene zigzag edges on Pt steps. We observe that the stress induced by the boundary is relaxed straining the Pt atoms bonded to the carbons which are only slightly distorted from its graphene ideal positions (see figure). The electronic structure shows a localized state on the graphene edge that expands into the flake few unit cells and only in one of the sublattices. No signs of local magnetic moments were found.

References [1] A.J. Martínez-Galera et al., Nano Letters, 11 (2011) 3576. [2] P. Sutter et al, Phys. Rev. B, 80 (2009) 245411. [3] M.M. Ugeda et al, Phys. Rev. Lett., 107 (2011) 116803. Figures

Figure 1: (Left panel) Experimental RT-STM image of a graphene flake on a Pt(111) step edge. (Central panel) Atomic structure of graphene zigzag edge on a Pt step calculated by a DFT method based on a plane wave basis set description (VASP). (Right panel) STM image with atomic resolution on the metal, the graphene and the boundary compared with the atomic structure calculated with DFT.


RKKY interactions in uniaxially strained graphene Stephen R. Power1, Paul D. Gorman2, John. M. Duffy2, Mauro S. Ferreira2, 3 (1) Center for Nanostructured Graphene (CNG), DTU Nanotech, Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark (2) School of Physics, Trinity College Dublin, Dublin 2, Ireland (3) CRANN, Trinity College Dublin, Dublin 2, Ireland spow@nanotech.dtu.dk Abstract The ease with which the physical properties of graphene can be tuned suggests a wide range of possible applications. Recently, strain engineering of these properties has been of particular interest [1]. Possible spintronic applications of magnetically doped graphene systems have motivated recent theoretical investigations of the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between localized moments in graphene [2]. In this work a combination of analytic and numerical techniques are used to examine the effects of uniaxial strain on such an interaction. A range of interesting features are uncovered depending on the separation and strain directions, and on how the localized magnetic impurity connects to the graphene lattice. For substitutional impurities we see a range of amplification and suppression effects as a function of strain, which maintain the sublattice dependent sign rules for the interaction in unstrained graphene (Fig 1). These features suggest that the strength of the interaction between two moments can be tuned or even switched on and off by minor levels of strain [3]. For adsorbed impurities a further range of features, including significant modification of the decay rate and the possibility of changing the sign of the interaction, are predicted [4]. In all cases, mathematically transparent expressions describing these features are derived which allow reliable predictions in agreement with numerical calculations. Since a wide range of effects, including overall moment alignment and magnetotransport response, are underpinned by such interactions, the ability to manipulate the coupling by applying strain may lead to interesting spintronic applications.

References [1] V. M. Pereira and A. H. Castro Neto, Phys. Rev. Lett., 103 (2009), 046801 [2] e.g. S. Saremi, Phys. Rev. B, 76 (2007), 184430, S. R. Power and M. S. Ferreira, Crystals, 3 (2013), page. 49-78 and references within. [3] S. R. Power, P. D. Gorman, J. M. Duffy and M. S. Ferreira, Phys. Rev. B 86 (2012), 195423. [4] P. D. Gorman, J. M. Duffy, M. S. Ferreira and S. R. Power, in preparation.


Figures

Fig 1: Ratio ( βA ) of strained and unstrained magnetic coupling between two substitutional magnetic impurities as a function of uniaxial strain (ξ ). The magnetic impurities are a fixed distance apart in the armchair direction. Numerical results are shown for strains applied parallel (red circles) and perpendicular (green squares) to this separation direction where suppression and amplification of the coupling are observed. The lines represent analytical predictions of the same quantities. Adapted from Ref [3].


Non-collinear magnetic moments in graphene with vacancies Stoyan Pisov, Vladislav Antonov, Ana Proykova University of Sofia, 5 James Bourchier Blvd., 1164 Sofia, Bulgaria anap@phys.uni-sofia.bg Abstract Although Nature does not favor low dimensional crystal growth, self-standing two-dimensional crystal films do exist – single, one-atom-thick layers of carbon and tungstenite are examples of truly twodimensional materials. Perfect graphene has an amazing band structure [1], which determines its fascinating properties – a zero DOS metal and, simultaneously, a zero gap semiconductor. The full symmetry of the system makes it possible to use the massless two-dimensional Dirac’s equation for the low energy state. Since the honeycomb lattice of graphene is a bipartite lattice, it can be partitioned into two mutually interconnected triangular sublattices. Each atom belonging to one sublattice is connected to the atoms in the other sublattice only and vice versa. However, if defects (vacancies) are present then the symmetry between the two sublattices is destroyed, which effectively adds a mass to the Dirac equation. As a result, the gap opens at K-points and new (doping) levels are generated. In this work we revisit the induced magnetism in defective graphene to focus on frustration that occur after the removal of one or more atoms from a graphene sheet. Graphene is nonmagnetic with negligible spin-orbit coupling that makes it ideal for spin-polarized transport. However, imperfections – impurities or vacancies - change electronic and magnetic properties [2,3,4] and enhance adsorption of gases [5]. The carbon atoms have either three (perfect hexagonal arrangement) or two nearest neighbors (in the case of a neighboring vacancy or if it is an edge atom). Because of this, the position of the missing atom plays an important role in passivation (or not) of the dangling bonds and graphene with vacancies becomes magnetic, either ferro- or antiferromagnetic depending on the vacancy distribution in the graphene sublattices [2,4]. Among physical systems that display collective macroscopic quantum phenomena, interacting spin systems are perhaps the most experimentally informative. In our computational approach, we consider that a vacancy is formed in a knock-on collision – proton or electron bombardment. The formation a single vacancy in graphene leaves three σ dangling bonds and it removes a π electron. We use spin-polarized density functional theory (Quantum Esspresso, [5]) to monitor the spin polarization. The density functional for exchange-correlation energy of the many electron system is the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). The k-point sets are generated automatically following the Monkhorst-Pack (MP) scheme. The wavefunctions at each k-point are represented by the numerical coefficients of a finite set of plane waves, determined by a kinetic energy cut-off at 55 Ry (≅ 748eV ). The vacuum layer thickness in the periodic boundary conditions is 12 A. The size of supercell – 16 Bohr radii - is large to minimize self interaction through periodic boundary conditions. The shape of the supercell is hexagonal to preserve the lattice symmetry. Gauge Including Projector Augmented Waves (GIPAW) norm conserving pseudopotential provided by the QE web site http://www.quantum-espresso.org/ was implemented. GIPAW is a DFT based method to calculate magnetic resonance properties, exploiting the full translational symmetry of crystals. Ab-initio calculations have been performed for different vacancy concentrations – from 12.5% down to 1%. The results show that when high density of k-points 30x30x1 is used then the total magnetization converges as a function of cell size to 1.53 µB for a single-atom vacancy. The maximum magnetic moment of 2 µB (one µB due to the quasilocalized state and one µB due to the dangling bonds) is obtained for the case of non-interacting moments induced at the vacancy positions and if only Γ=0 is used. As it can be expected from symmetry point of view, a double-vacancy defect preserves the zero magnetizaton of graphene. When the defect concentration is decreased below 3.1%, the spin density becomes€ non-uniformly distributed among the atoms around the vacancy. The spin density around one of the atoms is higher than the density around the other two atoms that move in a closer distance. Finally, we discuss whether the ‘‘multi-sublattice structure’’ is required for the occurrence of noncollinear arrangements in a quantum spin system.


References [1] Novoselov, K., Geim, A., Morozov, S., Jiang, D., Katsnelson, M., Grigorieva, I., Dubonos, S. and Firsov, A., Nature 438(7065) (2005) 197–200. [2] Yazyev O., Rep. Prog. Phys. 73 (2010) 056501. [3] Terrones, H.,Lv, R.,Terrones and Dresselhaus, M., Rep. Prog. Phys. 75 (2012) 062501 [4] Antonov, V., Borisova, D., Proykova, A., IJQC 113(6) (2013) 792–796 (Article first published online: 24 MAR 2012) DOI: 10.1002/qua.24078) [5] Giannozzi, P., J. Phys. Condens. Matter. 21 (2009) 395502-395521. [6] Antonov, V., Borisova, D., Pisov, S., Proykova, A., Nanoscience & Nanotechnology, 11 (2010) 17-19.

A plot of the difference between spin-up and spindown states for a single atom vacancy.

1.0% vacancies: the magnetic moment perpendicular to the graphene plane

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The total electron density – a sum of the spin-up and spin-down states – for a double vacancy

2.0% vacancies: the magnetic moments are not collinear (frustration)


Electronic and transport properties of kinked graphene Jesper Toft Rasmussen, Tue Gunst, Haldun Sevincli, Peter Bøggild, Antti-Pekka Jauho, and Mads Brandbyge Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark mads.brandbyge@nanotech.dtu.dk Abstract Nanostructures based on graphene have an enormous potential for applications. Especially in future electronic devices compatible with and extending silicon technology, due to the outstanding electronic transport properties of graphene [1]. However, it is crucial to modify the semimetallic electronic structure of graphene to exploit its full potential for many electronic applications: a band gap can be introduced by nanostructuring graphene. There are several ways of obtaining this gap. One such way is by forming graphene nanoribbons (GNRs) using etching [2], unzipping carbon nanotubes [3] or by growing them using self-assembly on metal substrates [4]. Bonding of H or other species to graphene with large coverage opens an insulating band gap at the adsorption sites due to sp3 hybridisation [5]. Finally, regular perforations, known as a graphene antidote lattice (GAL) [7] can open a band gap. Graphene is exceedingly sensitive to its surroundings. The substrate interactions, which make graphene cling to small features, may be exploited by manufacturing nanostructures in the substrate. Recently, Hicks et al. [8] demonstrated how arrays of 1D large band gap, semiconducting graphene nanoribbons corresponding to a width of ~1.4 nm can be formed in graphene on a step-patterned SiC substrate. Linear folds, where the graphene sheet is bulging up from the substrate, have been induced for graphene suspended over trenches by using heat treatment [9]. Thus, the sheet can obtain significant bends at certain places induced by the substrate interaction, substrate nanostructuring, and subsequent treatments [10]. In this work we consider the reactivity of linear bends in a graphene sheet, and the electronic transport properties of kinks resulting from the hydrogenation of bends. Our starting point is the generic graphene structure shown in Fig. 1a, which is inspired by the experimental observation of trench formation [9]. So far there have been only a few theoretical studies of the atomic geometry of hydrogenated ripple structures in unsupported, strain-induced, graphene ripples [11-15]. Adsorption of hydrogen on graphene involves a reaction barrier that needs to be overcome before the single hydrogen atom sticks to the graphene sheet. Several investigations based on DFT calculations show that atomic hydrogen adsorbs on-top on flat graphene with a barrier about 0.2 eV and binding energy in the range of 0.7–1.0 eV [11]. Local curvature, or bending, of a graphene sheet is known to increase the chemical reactivity presenting an opportunity for templated chemical functionalization [16]. Using first-principles calculations based on density functional theory (DFT, SIESTA [17]), we investigate the reaction barrier reduction for the adsorption of atomic hydrogen at sites in graphene with varying local radius of curvature. We find a significant barrier lowering (~15%) for realistic radii of curvature (~20 Å) and that adsorption along the linear bend leads to a stable linear kink as seen in Fig. 1b. The reduction in adsorption barriers is shown in Fig. 2. We compute the electronic transport properties of individual and multiple kink lines using TranSIESTA [18], and demonstrate how these act as efficient barriers for electron transport: A single kink with a equilibrium angle of 50 degrees reduces transmission by 83%. Two parallel kink lines form a graphene pseudo-nanoribbon structure with a semimetallic/semiconducting electronic structure closely related to the corresponding isolated ribbons; the ribbon band gap translates into a transport gap for electronic transport across the kink lines – Fig. 3. We finally consider pseudo-ribbon-based heterostructures and propose that such structures present a novel approach for band gap engineering in nanostructured graphene. The presented calculations suggest that once a single hydrogen atom has been adsorbed, the induced local kink and resulting increase in local curvature makes it easier for the following H to adsorb, thus creating a propagating kink formation. A full line of hydrogen atoms pins the structure and divides the electronic systems into different regions. The transmission function displays transport gap features corresponding to the isolated nanoribbon band gaps.


References 1. Novoselov et al., Nature, 490 (2012) 192-200. 2. Han et al., Phys.Rev.Lett., 98 (2007), 206805. 3. Xie et al., J.Am.Chem.Soc., 133 (2011), 10394-10397. 4. Cai et al., Nature, 466 (2010), 470-473. 5. Elias et al., Science, 323 (2009), 610-613. 6. Balog et al., Nat.Mater., 9 (2010), 315-319. 7. Pedersen et al., Phys.Rev.Lett., 100 (2008), 136804. 8. Hicks et al., Nat. Phys., 9 (2013), 49–54 9. Bao et al., Nat. Nanotechnol., 4 (2009), 562– 566 10. Neek-Amal and Peeters, Phys. Rev. B, 85 (2012), 195445

11. Hornekær et al., Phys. Rev. Lett., 97 (2006), 186102 12. Srivastava et al., J. Phys. Chem. B, 103 (1999), 4330–4337 13. Wang et al., Phys. Rev. B, 83 (2011), 041403. 14. Chernozatonskii and Sorokin, J. Phys. Chem. C, 114 (2010), 3225–3229. 15. Chernozatonskii et al., Appl. Phys. Lett., 91 (2007), 183103 16. Ruffieux et al., Phys.Rev.B, 66 (2002) 245416. 17. Soler et al., J. Phys.: Condens. Matter, 14 (2002), 2745–2779 18. Brandbyge et al., Phys. Rev. B, 65 (2002), 165401

Figures

Figure 1: (a) Smooth ripple-like structure where the first and last six rows of carbon-dimers are surface-clamped regions with a separation of L = 90 Å. Atomic hydrogen is adsorbed at positions I– VIII. (b) The resulting kinked graphene structure after hydrogen is adsorbed in lines at the most reactive position (II) corresponding to the smallest local radius of curvature. The four kinks divide the structure into five sections, S1–S5.

Figure 2: Calculated reaction barriers for hydrogenation of bent graphene as a function of the local radius of curvature (II–VIII in Figure 1a). Flat graphene (position I) has an infinite radius of curvature and is used to normalise the barriers. calculations are spinpolarised and allow for atomic relaxation. Figure 3: (Left) Band structures for H-passivated armchair ribbons with varying width, N. (Right) The electronic transmission functions for the corresponding pseudo-ribbons.


The effect of residual oxygen on the production of graphene by atmospheric pressure chemical vapor deposition Nicolas Reckinger, Jean-Franรงois Colomer Research Center in Physics of Matter and Radiation (PMR), University of Namur (FUNDP), Rue de Bruxelles 61, B-5000 Namur, Belgium. nicolas.reckinger@fundp.ac.be To be of use in industrial applications, large-area uniform graphene films of high structural quality must be produced at low cost. In that context, catalytic chemical vapor deposition (CVD) shows great promise to fulfill these objectives. The first demonstration of graphene growth by CVD was reported in 2009 on copper foils under low pressure [1]. In terms of simplicity and cost-effectiveness, atmospheric pressure CVD [2,3,4] is an interesting alternative to low pressure CVD since it avoids the use of vacuum systems. In the present work, the growth of graphene by atmospheric pressure CVD on copper foils with methane is explored. The focus is put on the necessity of using hydrogen during the cooling and growth steps (in addition to extra pure argon). First, it is observed that, in the absence of hydrogen during natural (slow) cooling, graphene is not obtained. By contrast, the addition of a small amount of hydrogen or fast cooling leads to appreciable graphene coverage. X-ray photoelectron spectroscopy evidences that natural cooling without hydrogen results in heavily oxidized and amorphized graphene. A likely explanation for this observation is the seemingly inevitable presence of residual oxygen from ambient air in the growth atmosphere, which strongly damages graphene upon too long exposure at high temperatures. Likewise, graphene formation is drastically inhibited if hydrogen is not present during the growth step. The conclusion is that, in these conditions, hydrogen must be present all along the process to prevent a re-oxidation of the copper surface during growth and also to protect graphene from etching by oxygen during natural cooling. In the best conditions, micrometer-sized graphene hexagons are formed [3]. Raman spectroscopy and scanning electron microscopy confirm that these domains are monolayer, bilayer or few-layer. The monolayer hexagons are found to be of excellent structural quality, as testified by the absence of D band in the Raman spectra. As a summary, even if the occurrence of oxygen can apparently not be avoided in simple atmospheric pressure CVD systems, its negative effects can be eluded by a careful dosing of hydrogen during the growth and cooling steps. In this way, graphene hexagonal domains of high structural quality can be synthesized.

References [1] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, Science 324, 1312 (2009). [2] I. Vlassiouk, M. Regmi, P. Fulvio, S. Dai, P. Datskos, G. Eres, and S. Smirnov, ACS Nano 5, 6069 (2011). [3] B. Wu , D. Geng , Y. Guo , L. Huang , Y. Xue , J. Zheng, J. Chen , G. Yu , Y. Liu , L. Jiang , and W. Hu, Adv. Mater. 23, 3522 (2011). [4] S. Bhaviripudi, X. Jia, M. S. Dresselhaus, and J. Kong, Nano Lett. 10, 4128 (2010).


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Figure 1: Optical microscopy of graphene on copper foils oxidized under air after thermal treatment on a heating plate (a) for natural cooling without hydrogen and (b) for natural cooling under hydrogen. Scale bars are 20 Âľm. (c) X-ray photoelectron C 1s spectrum of the two previous samples compared with graphite.

Figure 2: Raman spectrum of a typical monolayer graphene hexagon. Inset: optical microscopy image of the corresponding hexagon transferred onto 300-nm-thick SiO2.

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Figure 3: Scanning electron microscopy views of (a) monolayer and few-layer graphene hexagons on copper and (b) focus on a monolayer graphene hexagon.


Comparative study of graphene TEM sample preparation methods Ehsan Rezvani, Shishir Kumar and Georg Duesberg CRANN & School of Chemistry, Trinity College Dublin, Dublin, Ireland rezvanie@tcd.ie Abstract One of the key points in studying 2D materials e.g. graphene and its derivatives is obtaining clean largearea samples. Moreover, because graphene is a 2D material, its properties can be greatly influenced by its substrate. Transmission Electron Microscopy (TEM) offers one approach for preparing and investigating suspended graphene. Additionally, graphene-based TEM grids benefit from low background noise while at the same time providing firm support to large particles due to its outstanding strength and may be useful as a standalone commercial product [1]. A number of different approaches have been reported for transferring graphene onto TEM grids. The most commonly used method involves fishing graphene with a polymer support (usually poly methyl methacrylate, PMMA) onto a TEM grid and subsequently removing the polymer layer [2]. This produces large area samples but typically results in dirty graphene. Another technique is direct transfer of graphene without any polymer coating [3]. This method results in relatively clean graphene but with a very low yield. We have developed and investigated an alternative method to transfer graphene onto TEM grids, namely polymer evaporation. This is similar to the conventional polymer supported method but involves an additional step whereby PMMA is thermally evaporated under inert/reducing atmosphere. Here a comparative study of direct transfer vs. polymer evaporation is reported. The advantages and disadvantages of each approach are discussed and possible improvements/modifications are outlined. The results suggest that the polymer evaporation method offers higher yield, large area coverage (lateral dimensions as big as ~10Îźm are attainable) but some polymer residues are detectable. On the other hand, direct transfer has a much lower yield but provides a cleaner surface.

References [1] [2]

S Kumar and E Rezvani and V Nicolosi and G S Duesberg, Nanotechnology, 23 (2012), 145302. A. Reina, X. Jia, J. Ho, D. Nezich, H. Son, V. Bulovic, M. S. Dresselhaus, and J. Kong, Nano Lett., 9 (2009), 30–35. [3] W. Regan, N. Alem, B m g ii as a i a g Crommie, and A. Zettl, Appl. Phys. Lett., 96 (2010),113102. Figures Fig.1. Schematic representation of polymer evaporation technique Fig.2. Schematic representation of direct transfer technique


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Extremely high sensitive graphene sensor for NO2 detection at room temperature Maria Lucia Miglietta1, Filiberto Ricciardella1,2, Filippo Fedi3, Tiziana Polichetti1, Ettore Massera1, Nicola Lisi4, Rossella Giorgi4 and Girolamo Di Francia1 1

ENEA-UTTP-MDB Laboratory, C.R. Portici, Piazzale E. Fermi, 1, Portici (Naples), I-80055, Italy 2 University of Naples ‘Federico II’, Department of Physics, Via Cinthia, I-80126, Naples, Italy 3 University of Naples ‘Federico II’, Department of Materials and Production Engineering, Piazzale Tecchio, 80125 Naples, Italy 4 ENEA-UTTMAT-SUP Laboratory, C.R. Casaccia, via Anguillarese 301, I-00123 Roma, Italy filiberto.ricciardella@enea.it

Abstract Graphene is nowadays more and more the fulcrum of the research in physics and materials science for both fundamental research and applications, thanks to its unique and supreme properties. Being a twodimensional fabric and a surface without bulk, graphene has properties that make it sensitive to the environment and different gases. The sensing field has been showing particular interest due to the high sensitivity and flexibility of the material, the possibility to integrate graphene with other material and in portable devices. Herein we report on extremely high sensitive devices based on graphene derived by a liquid-phase exfoliation process. The employment of this technique, besides having a low environmental impact, is very powerful: (a) it does not require sophisticated equipments with high operating and production costs; (b) it provides a high yield in terms of few-layers graphene; (c) it represents a potentially scalable production of large quantities. The ongoing challenge is to obtain larger flakes of higher quality. To this aim, we prepared a colloidal suspension of graphene by dispersing 2.5 mg/mL of graphite powder (Sigma-Aldrich) in N-methyl-pyrrolidone (NMP) and sonicating in a low power bath (∼16 W) for about 168h. The unexfoliated graphite flakes were removed by centrifugation at 1000 rpm for 45 minutes and the top half of the surnatant was collected. The so-obtained colloidal suspension was characterized by Dynamic Light Scattering technique with a Zetasizer Nano (Malvern Instruments), that supplies information on the mean size of the dispersed flakes (~140nm). Raman analysis (Figure 1) was performed on graphene films prepared by drop-casting few microliters of the graphene solution on the top of oxidized silicon wafers. Analogously, chemiresistive devices were fabricated by drop-casting onto Al2O3 transducers with interdigitated Au contacts. Devices were mounted in a Gas Sensor Characterization System (Kenosistec) and tested towards 350 ppb of NO2 for 10 min in wet nitrogen with a flow of 500sccm at T=250C and relative humidity of 50%. The normalized conductance, reported in Figure 2a, shows the remarkable response of 27% with a signal-to-noise ratio (SNR) equal to. To the best of our knowledge this is the best performance reported in literature [1, 2]. The findings reported herein were compared to those obtained in a previous work where a much lower sonication time was used to exfoliate graphite (3h instead of 168h) [3]. As reported in several works by Coleman and coworkers [4, 5], a prolonged sonication time enriches the few layer content, that is the most sensitive fraction of the resultant films. The improvement of the graphene flakes concentration results in an overall improvement of the sensing performances with a conductance response (Figure 2a) up to 5-6 times higher than that shown in Figure 2b. At the aim of understanding the actual interaction mechanism operating on the multilayer system presented above, further investigations are ongoing to compare its performances with those of a sensor device based on a single layer of graphene realized by CVD. Preliminary results seem to confirm the key role of the material fabrication process into the device chemical response.

References [1] G. Lu, S .Park, K. Yu, R. S. Ruoff, L. E. Ocola, D. Rosenmann, and J.Chen, ACS Nano, 5 (2011) 1154-1164 [2] A. Serra, A. Buccolieri, E. Filippo, D. Manno, Sensors and Actuators B, 161 (2012) 359-365 [3] M. L. Miglietta, E. Massera, S. Romano, T. Polichetti, I. Nasti, F. Ricciardella, G. Fattoruso, G. Di Francia, Procedia Engineering, 25 (2011) 1145-1148 [4] J. Colemann, Acc Chem Res., 46 (2013) 14-22 [5] U. Khan, A. O’Neill, M. Lotya, S. De, J. N. Coleman, Small, 6 (2010) 864


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Figure 2: Conductance response upon exposure to 350ppb of NO2 for 10 min in wet environment at 25째C related to sensing materials exfoliated by bath sonication for: a) 168 h; b) 3 h.


Hysteretic transport in manganite/graphene hybrid planar nanostructures Mirko Rocci1,2, J. Tornos1,2, N.M. Nemes1,2, A. Rivera-Calzada1,2, Z. Sefrioui1,2, M. Clement2,3, E. Iborra2,3, C. León1,2, M. García Hernández4 and J. Santamaría1,2 1

CEI Campus Moncloa, UCM-UPM, Madrid, Spain. G.F.M.C., Facultad de Ciencias Físicas – Universidad Complutense de Madrid, Madrid 28040, Spain 3 G.M.M.E., E.T.S.I.T., Universidad Politécnica de Madrid, Madrid 28040, Spain 4 Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Cantoblanco 28049, Spain

2

mirko.rocci@fis.ucm.es Abstract We report on the fabrication and magnetotransport characterization of innovative hybrid graphenebased planar nanodevices with epitaxial nanopatterned La0.7Sr0.3MnO3 manganite, grown on SrTiO3 (100), as ferromagnetic current injector electrodes. The few layers graphene (FLG) was deposited onto the predefined manganite nanowires by using the PMMA transfer technique. These nanodevices exhibit hysteretic transport as measured by IV curves. The resistance can be reversibly switched between high and low states yielding a consistent non-volatile memory response.

1. Introduction Since their discovery, colossal magnetoresistance manganites have focused a large research effort due to the interesting physics underlying the strong electronic correlations. In particular, the half metallic character of La0.7Ca0.3MnO3 (LCMO) or La0.7Sr0.3MnO3 (LSMO) perovskite oxides has motivated their use as sources of spin polarized carriers in spintronic devices. Although many examples can be found in the literature were these oxides have been used as magnetic electrodes in multilayer devices for perpendicular transport along 3D pillars, planar devices involving nanostructured electrodes are to our knowledge very scarce [1]. This may be related to difficulties in nanostructuring these materials due to their mechanical hardness, or to the alteration of their electronic properties caused by etching processes. Yet, having access to single domain manganite wires could be of interest for non local spin injection. In this communication we report on our recent effort on fabricating complex oxide nanostructures.

2. Materials and Methods The 18 nm c-axis LSMO thin film samples were grown on (001)-oriented SrTiO3 single crystals in a high-O2-pressure (3.4 mbar) r.f. sputtering system at 900 °C. In situ annealing was done in 800 mbar O2 pressure and 550 °C for 30 min [2]. LSMO wires 200 and 500 nm wide were fabricated by using conventional Electron Beam Lithography and wet etching processes. In particular, 200nm thick maN2403 negative resist (from MicroResist GmbH) was spun on the LSMO thin film and 10 kV, 100 pA electron beam lithography parameters were used in order to define the manganite nanowires. The LSMO wet etching was done diping the sample in a hydroclhoridryc acid solution for few seconds. The mechanically exfoliated FL-graphene on SiO2/Si wafer was moved onto predefined La0.7Sr0.3MnO3 manganite nanowires by using the PMMA transfer technique (fig.1a).

3. Results and Discussion The magnetic behaviour is examined by measurements of the anisotropic magnetoresistance AMR in magnetic fields with various orientations with the direction of the wire. In LSMO wires we find evidence for a magnetic state up to room temperature and resistivity values close to those found in large thin films, suggesting that the electronic state is little affected by the lithography process. Different coercive field values were found as function of the nanowire width. Abrupt resistance switching at coercivity is consistent with a single domain state. For magnetic fields oriented perperdicular to the wire AMR displays complex futures suggesting domain wall resistivity. The resistivity vs temperature measurement shows a typical metal-insulator transition (MIT) acompanied with a strongly non linear transport with hysteretic IV curves characteristic. In particular, we find a typical memristive-like behaviour in the metallic regime and pinched-diode behaviour in the insulator regime (fig.1b). Interestingly, the bistable resistance states display a nonvolatile memory response.

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4. Conclusions New kind of hybrid LSMO/FLG nanodevices were fabricated and characterized. A peculiar hysteretic transport has been found at temperatures ranging from 10 to 300 K. This behaviour could be related to the contact resistance between the oxide and the graphene and could be used in the future as graphene-based non-volatile memory, in nanoelectronic applications. Further work will be necessary to identify the origin of such an intriguing response in these complex oxide/graphene nanostructures.

References [1] Luis E. Hueso, José M. Pruneda, Valeria Ferrari, Gavin Burnell, José P. Valdés-Herrera, Benjamin D. Simons, Peter B. Littlewood, Emilio Artacho, Albert Fert & Neil D. Mathur. Nature 445, 410 (2007) [2] F. Y. Bruno, J. Garcia-Barriocanal, M. Varela, N. M. Nemes, P. Thakur, J. C. Cezar, N. B. Brookes, A. RiveraCalzada, M. Garcia-Hernandez, C. Leon, S. Okamoto, S. J. Pennycook, and J. Santamaria. Phys. Rev. Lett. 106, 147205 (2011)


Study of the substrate influence on the properties of physisorbed self-assembled molecular layers: Azabenzene 1,3,5-Triazine on graphite and graphene on metals 1

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Lucía Rodrigo , Pablo Pou , Antonio J. Martínez-Galera , José M. Gómez-Rodríguez 1 and Rubén Pérez

2

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Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E 28049 Madrid, Spain; 2 Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E -28049 Madrid, Spain lucia.rodrigo@uam.es

Abstract The properties of molecular overlayers on inorganic substrates depend on a delicate balance between intermolecular and overlayer-substrate interactions [1]. Here we present a combined experimental and theoretical study of azabenzene 1,3,5-Triazine layers grown on both graphite and graphene on Pt(111). VT-STM experiments (see fig. 1) show large overlayer islands with Moiré structures on both substrates [2]. While in both cases the last layer is graphene, the atomic arrangements, the measured molecule diffusion barriers and the growing properties are different [2]. This system is, therefore, a perfect model for the study of the properties of physisorbed self-assembled molecular layers [1]. We have carried out ab initio DFT calculations (using VASP) trying with all the functionals available (LDA, PBE and hybrids) and different approaches for the van der Waals interactions [3] to fully characterize the intermolecular (H bonds and vdW) and molecule-substrate (vdW attraction and Pauli repulsion) interactions (see fig. 2). We have found that the graphene layer, even for these physisorbed molecules, modifies the intermolecular interactions respect to an isolate layer but not significant differences are found between graphite and graphene on Pt substrates. This exhaustive characterization shows the theoretical limitations to describe these weakly interacting systems even with state-of-the-art approaches.

References [1] Forrest et al, ChemRev, 97, 1793 (1997); Hooks et al, AdvMat, 13, 227 (2001) [2] Martinez-Galera et al, JPhysChemC, 115, 11089 (2011); JPhysChemC, 115, 23036 (2011) [3] S. Grimme et al, J Comp Chem, 27 (2006) 1787; Klimes et al, J Phys: Condens Matter, 22, 022201 (2010) Figures

Figure 1. VT-STM experimental image of the graphene + Pt system


Figure 2. Ball-stick scheme of the theoretical simulation for the graphene + Pt system


On the understanding of graphene oxide structure 1

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Rodríguez-Pastor I. , Ramos-Fernández G. , Varela-Rizo H. , Gutiérrez H. R. , Chong H.M.H. , 4 1 Terrones M. , Martín-Gullón I. * 1

Chemical Engineering Dept., University of Alicante, Ctra. de San Vicente s/n 03690 Alicante, Spain Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA 3 Nano Research Group, School of Electronics and Computer Science, University of Southampton, Highfield, SO17 1BJ Southampton, United Kingdom 4 Department of Physics, Department of Materials Science and Engineering & Materials Research Institute, The Pennsylvania State University, 104 Davey Lab., University Park, PA 16802-6300, USA 2

*gullon@ua.es

Abstract The mass-production of graphene has been one of the most important aims of the scientific community in recent years. Attempts via top-down or bottom-up methods were proposed to get an affordable graphene. There is a general agreement that top-down methods based on the chemical route, yielding graphene oxide (GO), offer a possibility for large-scale and high-production of graphene-based materials, as well as large sheet dimensions [1]. Besides the weakness of its insulating properties and the defects in its structure, it also present the big strengths of the ease of handling of the solution process of GO, the control of the number of layers, and the capacity of tuning by chemical functionalization [2], valid for most of the high-consumption applications. Besides, partial recovery of the electrical conductivity can be achieved by chemical or thermal reduction [3]. These properties enable the use of GO and reduced GO in applications such as reinforced nanocomposites, transparent conductive films or biosensors. The structure and chemistry of GO has been widely studied but is still uncertain. GO is a honeycomb lattice decorated with functional groups and defects but the structural models proposed are unambiguous [4], including the possibility of incorporating some self-surfactant compounds [5]. The structure of the final product depends on different factors. The nature of the starting material (crystallinity, size) [6], or synthesis procedure (intercalation and oxidant agents) have influence on the morphology and composition of GO [7]. In this work we present a study of the GO obtaining in an effort to deep into elucidating the structure. GO is obtained from two different graphitic precursors, natural graphite flakes and a carbon nanomaterial. Three different classic methods involving different oxidant agents have been compared: modified Hummers-Offeman (KMnO4/H2SO4) [8], Brodie (HNO3/NaClO3) [9] and Staudenmaier (H2SO4/HNO3/NaClO3) [10]. The effectiveness of the oxidation plus exfoliation was evaluated, together with a deep characterization (XPS, NMR, Raman, HR-TEM, TG-MS) to analyze the effect of each method over each precursor in the resultant physical and chemical structure. TEM exploration of exfoliated GO reveals noteworthy differences among the product of the abovementioned methods showing higher quality crystals for GO obtained by modified HummersOffeman. Multiple peak-fit for Raman Spectra helps on the understanding of the morphology and composition of GO. Deconvolutions show variations in Raman shift for each method indicating different introduction of functional groups and distinct effectiveness of the oxidation treatment. Also TG-MS signal and the quantification derived indicate variations in the mechanisms of the three oxidations.

References [1] Zhu, Y., S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, and R.S. Ruoff, Advanced Materials, 35 (2010) p. 3906. [2] Loh, K.P., Q. Bao, G. Eda, and M. Chhowalla, Nature Chemistry, 12 (2010) p. 1015. [3] Gómez-Navarro, C., R.T. Weitz, A.M. Bittner, M. Scolari, A. Mews, M. Burghard, and K. Kern, Nano Letters, 11 (2007) p. 3499. [4] Dreyer, D.R., S. Park, C.W. Bielawski, and R.S. Ruoff, Chemical Society Reviews, 1 (2010) p. 228.


[5] Rourke, J.P., P.A. Pandey, J.J. Moore, M. Bates, I.A. Kinloch, R.J. Young, and N.R. Wilson, Angewandte Chemie International Edition, 14 (2011) p. 3173. [6] Botas, C., P. Álvarez, C. Blanco, R. Santamaría, M. Granda, P. Ares, F. Rodríguez-Reinoso, and R. Menéndez, Carbon, 1 (2012) p. 275. [7] Chua, C.K., Z. Sofer, and M. Pumera, Chemistry - A European Journal, 42 (2012) p. 13453. [8] Varela-Rizo, H., I. Rodriguez-Pastor, C. Merino, and I. Martin-Gullon, Carbon, 12 (2010) p. 3640. [9] Brodie, B.C., Quarterly Journal of the Chemical Society of London, 1 (1860) p. 261. [10] Staudenmaier, L., Ber Dtsch Chem Ges, (1898) p. 1481.


Two-step graphitization affords full repair of defects in reduced graphene oxide films R. Rozada, J.I. Paredes, S. Villar-Rodil, A. Martínez-Alonso, J.M.D. Tascón

Instituto Nacional del Carbón, INCAR-CSIC, Apartado 73, 33080 Oviedo, Spain rozada@incar.csic.es

Abstract Graphene obtained through the so-called graphite oxide route (i.e., reduced graphene oxide) contains a significant number of defects and residual oxygen functionalities that severely degrade many of their properties, such as the electrical conductivity. Despite efforts to achieve full restoration of the perfect carbon lattice in this type of graphene, such a goal has so far remained elusive by using the implemented reduction approaches and some alternative strategies. Here, we demonstrate the complete restoration of the carbon lattice in chemically reduced graphene oxide sheets assembled into free-standing, paper-like films through a graphitization approach (i.e., high temperature annealing). By means of a carefully designed heat treatment protocol and extensive characterization of the films by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and scanning tunneling microscopy (Fig. 1) we conclude that there are two main stages in the transformation of the films during their graphitization: (i) full removal of residual oxygen functional groups from the chemically reduced graphene oxide sheets and ensuing generation of atomic vacancies (first annealing step, temperatures of 1500 oC) (ii) annihilation of the atomic vacancies and coalescence of adjacent overlapping sheets to form continuous polycrystalline layers in the film (second annealing step, temperatures between 1800 and 2700 oC). For the highly graphitized films, the individual domains in the polycrystalline layers exhibit long-range graphitic order, are free of even point defects and their size is mainly determined by the dimensions of the starting reduced graphene oxide sheets (a few to several hundred nanometers). The prevailing type of defect in the polycrystalline layers are thus the grain boundaries separating neighboring domains. These films exhibit electrical conductivity values as high as 577,000 S m-1, which are about 1-2 orders of magnitude larger than those typical of graphene oxide films reduced by chemical or other means.

References [1] Rozada R., Paredes J.I., Villar-Rodil S., Martínez-Alonso A., Tascón J.M.D., Nano Research, 3 (2013), pp 216-233. [2] Ghosh T., Biswas C., Oh J., Arabale G., Hwang T., Luong N.D., Jin M., Lee Y.H., Nam J.-D, Chemistry of materials, 24 (2011), pp 594-599.


Figures

Figure 1: (a-c) Starting free-standing, paper-like film. (d-f). Free-standing, paper-like film first annealed at 1500 oC and then annealed again at 2700 oC. (a,b) Digital photographs. (b,e) Nanometer scale STM images. Typical tunneling parameters: 100-300 pA (tunneling current) and 1500 mV (bias voltage). (c,f) Atomic-scale STM images. Typical tunneling parameters: 1-2 nA (tunneling current) and 5-100 mV (bias voltage).


Aqueous phase exfoliation of graphite by cellulose nanocrystals 1

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Virginia Ruiz , Pedro Mª Carrasco , Sarah Montes , Maryam Borghei , Ibon Odriozola , Germán 1 Cabañero 1

New Materials Department, IK4-CIDETEC, Paseo Miramón 196, 20009 San Sebastián, Spain 2 Department of Applied Physics, Aalto University, P.O.Box 15100, FI-00076 Aalto, Finland vruiz@cidetec.es

Producing processable graphene flakes in large quantities remains an ongoing challenge for large-scale applications. To that end, top-down approaches such as the exfoliation of powdered graphite in the liquid phase is a very promising route due to its simplicity, utilization of low-cost and readily available graphite, upscaling potential, integration with other processes such as blending or casting and no need of transferring processes from the growth substrate. In essence, liquid phase exfoliation (LPE) involves exfoliation of graphite by simple sonication to produce graphene sheets dispersed in a solvent [1]. As graphene sheets tend to restack due to strong Van der Waals forces, the sheets need to be stabilized by different means such as covalent functionalization or the use of various stabilizers such as surfactants [2], polymers [3] and aromatic molecules [4]. The most common route for LPE involving graphite functionalization is graphite oxidation followed by exfoliation in water to yield graphene oxide, which is subsequently reduced to obtain reduced graphene oxide whose properties differ from pristine graphene. On the other hand, direct exfoliation of unfunctionalized graphite by sonication and good dispersion of produced graphene sheets require the use of stabilizers that interact noncovalently with graphene and prevent their stacking. In this regard, the development of novel exfoliating agents and stabilizers that are widely available, lowcost, environmentally-friendly and biodegradable would definitely bring LPE one step closer towards industrial viability. To this end, we have demonstrated that nanoscale cellulosic fillers, called cellulose nanocrystals (CNC) are very efficient for graphite exfoliation and stabilization of resulting graphene flakes in aqueous dispersions at high concentrations. CNCs can be regarded as very promising graphene stabilizers due to their interesting features such as low density, high surface area, good mechanical properties, biodegradability and availability from renewable resources, which has triggered rising interest during the past decade in these nanocellulose materials especially for nanoreinforcement and barrier property improvement in polymer matrices. Moreover, CNC can be obtained from cellulose, the most abundant biomass material in nature, which can be extracted from natural fibers, among other sources. Here we have produced CNC from microcrystalline cellulose (MCC) by acidic hydrolysis. We will show that graphite can be effectively exfoliated and stabilized in aqueous CNC dispersions at very high concentrations by applying tip sonication for very short times (less than 4 h). Unexfoliated graphite is removed by centrifugation and the resulting dispersions are stable for months without noticeable precipitate. CNC-stabilized graphene dispersions have been characterized by FESEM, TEM, UV-Vis absorption and Raman Spectroscopy. Figure 1 show representative FESEM and TEM images of the exfoliated samples. In samples produced at large ratios of CNC to initial graphite concentration, cellulose nanocrystals are clearly visible as small whiskers covering the surface of the graphene flakes in the SEM image. Overall, TEM reveals the presence of large sheets of up to several micrometers in length whose size decreased with sonication time. We will show that the effectiveness of CNC as graphene stabilizers depends largely on the size and functionalization degree of the nanocrystals. Other parameters, such as the concentration of stabilizer and starting graphite as well as their concentration ratio, have been optimized in order to increase both final graphene concentration and graphene/stabilizer ratio. In the optimal conditions, stable 1.7 mg/mL graphene dispersions with remarkably high ratios of graphene to CNC concentration (up to 5.4) have been obtained, an aspect that is crucial as an excess of stabilizer can affect adversely the mechanical, thermal and electrical properties of graphene-based composites.

References [1] Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z. Y.; De, S.; McGovern, I. T.; Holland, B.; Byrne, M.; Gun’ko, Y. K.; Boland, J. J.; Niraj, P.; Duesberg, G.; Krishnamurthy, S.; Goodhue, R.; Hutchison, J.; Scardaci, V.; Ferrari, A. C.; Coleman, J. N.; Nat. Nanotechnol., 3 (2008) 563. [2] Lotya, M.; King, P. J.; Khan, U.; De, S.; Coleman, J. N.; ACS Nano, 4 (2010) 3155.


[3] Wajid, A. S.; Das, S.; Irin, F.; Ahmed, H. S. T.; Shelburne, J. L.; Parviz, D.; Fullerton, R. J.; Jankowski, A. F.; Hedden, R. C.; Green, M. J.; Carbon, 50 (2012) 526. [4] Das, S.; Irin, F.; Tanvir Ahmed, H. S.; Cortinas, A. B.; Wajid, A. S.; Parviz, D.; Jankowski, A. F.; Kato, M.; Green, M. J.; Polymer, 53 (2012) 2485.

Figures

Figure 1. FESEM (left) and TEM (right) images of exfoliated graphene flakes by cellulose nanocrystals. Inset: photograph of CNC-stabilized graphene aqueous dispersion


Novel highly conductive graphene-based materials S. Russo, I. Khrapach, F. Withers, T. H. Bointon, D. K. Pplyushkin, W. L. Barnes, M. F. Craciun Centre for Graphene Science, University of Exeter, Exeter (UK) s.russo@exeter.ac.uk The development of future flexible and transparent electronics relies on novel materials, which are mechanically flexible, lightweight and low-cost, in addition to being electrically conductive and optically transparent. Currently, tin doped indium oxide (ITO) is the most wide spread transparent conductor in consumer electronics. The mechanical rigidity of this material limits its use for future flexible electronic applications. The leading candidates to substitute ITO are graphene based materials. Graphene is an atomically thin conductive, transparent and flexible material. However, the use of graphene as a truly transparent conductor remains a great challenge because the lowest values of its resistivity demonstrated so far are above the values of commercially available ITO. Chemical functionalization of graphene offers a simple way to improve the electrical properties of these materials. Here we report novel graphene-based transparent conductors obtained by intercalating few-layer graphene (FLG) with ferric chloride (FeCl3). Through a combined study of electrical transport and optical transmission measurements we demonstrate that FeCl3 enhances the electrical conductivity of FLG by two orders of magnitude while leaving these materials highly transparent. We find that the optical transmittance in the visible range of FeCl3-FLG is typically between 88% and 84%, whereas the resistivity is as low as 8.8 Ω. These parameters outperform the best values found in ITO (i.e. resistivity of 10 Ω at an optical transmittance of 85%), making therefore FeCl3-FLG the best candidate for flexible and transparent electronics. The temperature and magnetic field dependence of the electrical transport 14 -2 properties show that this material is metallic with typical carrier concentration of n=3x10 cm and macroscopic hole mean free path close to 1μm. Analysis of Shubnikov-de Haas oscillations together with Raman spectroscopy show decoupling of FLG into isolated graphene monolayers providing several parallel hole gas. The unique combination of record low resistivity, high optical, transparency and macroscopic room temperature mean free path has not been demonstrated so far in any other doped graphene system, and opens new avenues for graphene-based optoelectronics.

References [1] I. Khrapach, F. Withers, T. H. Bointon, D. K. Pplyushkin, W. L. Barnes, S. Russo, M. F. Craciun, Adv. Mater. 24, 2844 (2012).


(Two page abstract format: including figures and references. Please follow the model below.) Coupling Graphene with Polymers Horacio J. Salavagione,1 Marta Castelaín,1 Gerardo Martínez,1 José L. Segura,2 Gary Ellis1 1. Instituto de Ciencia y Tecnología de Polímeros (ICTP- CSIC). C/ Juan de la Cierva, 3. 28006, Madrid. Spain. 2. Dpto. de Química Orgánica. Facultad de Química. Universidad Complutense de Madrid. E28040, Madrid-Spain. e-mail: horacio@ictp.csic.es

Abstract Nowadays the concept of synergy through the combination of different materials is one of the most successful approaches at the frontiers of materials technology. In this respect, the combination of graphene with polymers provides a powerful tool for the creation of materials with countless applications almost in a combinatorial manner, because it does not only refer to the combination of two compounds but in the assembly of two families of materials.   The covalent route to connect graphene with polymers represents an interesting alternative to the conventional mixing methods for the development of novel composite materials with a compendium of interfacial interactions [1]. In this type of nanocomposites the concept of interface changes from a traditional view of molecular interactions between components at a polymer – filler interface (e.g. van der Waals, hydrogen bonding, halogen bonding, etc.), to the concept of a single compound where graphene forms an integral part of the polymeric chain [2]. Here, a series of synthetic approaches to covalently attach graphene and polymers are presented. These methods include alkyne-azide and thiol-yne click reactions as well as nitrene chemistry. While the click reactions need the previous modification of graphene with clickable polymers, the others involve the direct coupling of polymers to graphene. These reactions also occur in graphene immobilized on surfaces [3] and, as some of them require the use of thermal or photochemical initiators, polymer brushes patterns on graphene surface can be obtained. References [1] H. J. Salavagione, G. Martínez, G. Ellis, Macromol. Rapid Commun. 32 (2011) 1771. [2] H. J. Salavagione. “Innovative Strategies to Incorporate Graphene in Polymer Matrices: Advantages and Drawbacks from an Applications Viewpoint” in “Innovative Graphene Technologies: Developments & Characterisation” Volume 1. Ed. A. Tiwari. Rapra-Smithers, UK,2013 [3] Z. Jin, T. P. McNicholas, Chih-Jen Shih, Q. H. Wang, G. L. C. Paulus, A. J. Hilmer, S. Shimizu, M. S. Strano, Chem. Mater., 23 (2011) 3362


Changes in the properties of graphene produced by metal contacts investigated by Raman spectroscopy and transport experiments I. Serrano-Esparza1,2, J.M. Michalik1,2, J. Fan1,2, M.R. Ibarra2,3 and J.M. de Teresa1,2,3 1

Instituto de Ciencia de Materiales de Aragón, Facultad de Ciencias, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain 2 Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain 3 Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50009 Zaragoza, Spain iserranoe@unizar.es Abstract It’s important to study how graphene behaves when different metals are deposited over it to control exactly the operation of future graphene-based nanodevices, which could be affected by this interaction. A priori, we would expect some doping caused by the difference in work function between the metal and graphene, which would alter the electron-phonon interaction. Raman spectroscopy -- a non-invasive method that completely characterises graphene through different peaks corresponding to vibrational modes and that are used to determine the quality of the sample — is the most effective way to detect this change in the electron-phonon interaction [1]. In this work, we show Raman spectra for different samples: first, we exfoliated graphene over 285nm of SiO2 substrates; second, we evaporated 3nm of metals by electron beam evaporation over graphene flakes. The changes on Raman spectra obtained for both G and 2D peaks don’t correspond to what we would expect due to differences in work function but must be explained by other phenomena, for example, stress. For Co, two new peaks appear at the Raman spectrum (see figure 1). A study over time was carried out to check whether the new peaks were a consequence of stress or had another origin. We soon rejected the first option and opted for a strong bonding between graphene and cobalt that could introduce new vibrational modes; in fact, some theoretical studies [2], [3], [4] show that Co (0001) and Ni (111) are chemisorbed over graphene –with a much smaller binding distance--, whereas most other metals are just physisorbed. Finally, to study the electronic properties of Co over graphene grown by CVD, we produced some devices by electron beam lithography (figure 2). The first results indicate clear changes in the Dirac-point curve, obtained by means of an applied back voltage. References [1] A. Ferrari. Solid State Communications. 143 (2007) 47- 57 [2] S. M. Kozlov et al. Phys. Chem. C 116 (2012) 7360-7366 [3] A. Allard et al. Nano Lett. 10 (2010) 4335-4340 [4] G. Giovannetti et al. Phys. Rev. Lett.101 (2008) 026803


Figures

Figure. 1: Raman spectrum of a cobalt-graphene sample (normalized to the G peak intensity after background removal).

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Figure 2: Graphene based device with 3nm Co layer.


Isolated grafted graphenes via intercalation 1,2

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Takuya Morishita , Adam J Clancy , Milo S P Shaffer 1

Department of Chemistry, Imperial College London, London, SW7 2AZ, UK 2

Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan. t.morishita@imperial.ac.uk; m.shaffer@imperial.ac.uk

Graphenes have recently attracted attention as superior nanofillers for polymer composites, owing to their intriguing high mechanical, electrical, and thermal properties. Covalent functionalisation of graphene with polymers is an attractive route to realising improved properties in such systems and other bulk applications. Here, we synthesize graphenes grafted with long alkyl chains, by reacting Na-reduced graphites with alkyl halides. The effect of alkyl chain length, stoichiometry, and halide species on the degree of functionalisation of the alkylated graphenes obtained has been evaluated. Increasing the alkyl chain length of alkyl halides led to large decrease of the functionalisation degree, demonstrating that steric factors play an important role in determining the outcome of these reactions. However, the degree of functionalisation can be significantly improved, even in the case of using long alkyl halides such as eicosyl bromides, by using particular carbon/Na (C/Na) ratios in the reaction; the optimum balances total charge and charge condensation effects. The obtained eicosylated graphenes showed improved dispersibility in organic solvents, and a very high yield of single functionalised monolayers. This approach is very promising for preparing large quantities of graphenes with minimal damage to the carbon framework, avoiding the severe oxidation or sonication associated with other routes.

Schematic synthesis of graphene grafted via an in situ functionalisation of Na-reduced graphite.


Electronic structure calculations on MX2 dichalcogenide/Graphene hybrid structures. 1

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J. A. Silva-Guillén , E. Cappelluti , R. Roldán , F. Guinea , P. Ordejón

1

1. Centre d'Investigació en Nanciència i Nanotecnologia - CIN2 - (CSIC-ICN). 08193 Barcelona, Spain 2. Instituto de Ciencias de Materiales de Madrid - ICMM - (CSIC). 28049 Madrid, Spain jsilva@cin2.es Abstract Since the first isolation of graphene in 2004 [1] there has been much effort in exploiting its outstanding electronic properties [2] to technological applications, in particular, in combination with other two-dimensional crystals. There have been many studies of the Boron Nitride (BN)/graphene interaction due to the small mismatch between both of them that avoids graphene losing its electronic properties [3]. Nowadays, transition metal dichalcogenides (TMDC) such as MoS2 and WS2 are bringing much attention due to the fact that, although in nature they exhibit a bulk structure, they are layered materials which can be exfoliated like graphene to produce 2D single or multi-layer structures [4]. Interestingly, they are semi-conductors with a change in their electronic structure properties when changing from bulk (which presents an indirect gap) to a single layer (with a direct gap). This opens up new possibilities for the creation of new electronic and optoelectronic devices. The small mismatch between MoS2 and WS2 with graphene, also opens a wide possibilty of creating new devices. Recently, two papers by Britnell et al. [5] and Georgiu et al. [6] have shown good performance in FETs fabricated using this MoS2/graphene and WS2/graphene hybrid structures. Here, we present ab-initio DFT calculations (done using the Siesta code [7]) of the electronic properties of single-, multi-layer and bulk MoS2 and WS2. We also study the interaction of these materials with graphene and the possibility of fabricating new devices with these hybrid structures [4,8]. For this, we first study the interaction of a single layer of MoS2 or WS2 with graphene (Fig. 1 and 2). We find the optimal distance between graphene and MoS2 and WS2 and show that an interface dipole is created between them. We also find that the electron density distortion is inhomogeneous, following the mismatch between the graphene and WS2 lattices. Finally, we study the change of this properties when changing the number of layers of MoS2 and WS2 in the system. References [1] K. S. Novoselov, et al., Science 306 , 666 (2004). [2] A. H. Castro Neto, et al., Rev. Mod. Phys. 81 , 109 (2009). [3] M. Bokdam, et al. Nano Letters 11, 4631-4635 (2011) [4] Q. H. Wang, et al., Nature Nanotechnology 7 , 699 (2012). [5] L. Britnell, et al., Science 335 , 947 (2012). [6] Georgiu, et al. ArXiV 1211.5090 (2012). [7] J. M. Soler, et al., Journal of Physics: Condensed Matter 14 , 2745 (2002). [8] Y. Ma, et al., Nanoscale 3 , 3883 (2011).


Figures

Figure 1: Side view of the TMDC/graphene structure. Carbon is represented in blue, tungsten (molybdenum) in green and sulphur in yellow.

Figure 2: Top view of the TMDC/graphene structure. Carbon is represented in blue, tungsten (molybdenum) in green and sulphur in yellow.


A general method to transfer graphene with pick-and-place capability to soft surfaces: top electrodes for organic electronics and artificial graphite intercalation compounds a)†

Jie Song, b,c)

Lim,

Fong-Yu Kam, b)

Peter K.H. Ho,

a)†

Rui-Qi Png,

b)

b)

b)

Wei-Ling Seah, Jing-Mei Zhuo,

Geok-Kieng

a,b)*

and Lay-Lay Chua,

a) Department of Chemistry, National University of Singapore, Lower Kent Ridge Road, S117543, Singapore

b) Department of Physics, National University of Singapore, Lower Kent Ridge Road, S117542, Singapore

c) Primary address: DSO National Laboratories, 20 Science Park Drive, Science Park I, Singapore 118230, SINGAPORE

These authors contributed equally to the work.

* Electronic mail: chmcll@nus.edu.sg songjie@nus.edu.sg

Abstract Recent advances in the chemical vapor deposition growth of graphenes on metal foils have made large graphene sheets available for research and development. For real applications to electronic devices however, further breakthroughs in the method of graphene transfer from its growth substrate to the application substrate are necessary. Although various methods have been developed, a general way to transfer these graphenes reliably onto arbitrary surfaces, including “soft” ones, with registration, is still not available. Here we report a general transfer method that uses a generic self-release layer (SRL) in conjunction with a conventional poly(dimethylsiloxane) elastomer stamp.

This can transfer graphene with registration to

almost all surfaces, including fragile polymer thin films and hydrophobic surfaces which were previously not possible. We demonstrate high-fidelity graphene monolayer transfer onto 45nm-thick polymer dielectric films.

This gives capacitors that show superior dielectric

breakdown field strength over the ones with evaporated metal electrodes.

We integrate

graphene as top-gate electrodes into conventional organic field-effect transistors to achieve low-voltage operation using a sub-100-nm-thick gate dielectric layer made from conventional dielectric polymers. We also demonstrate a first “artificial” graphite intercalation compound (GIC) by stacking graphene monolayers alternately with a well-defined molecular intercalant of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). This GIC is p-doped by partial hole transfer from F4TCNQ (0.0035 per carbon), exhibits good electrical conductivity (400 ohm per square • sheet) and excellent thermal and humidity stability up to 175ºC. The transfer methodology is also applicable to other 2D materials and ultrathin metal films.


Diffusion-Assisted Synthesis of Graphene Søren Stærke, Bjarke Jørgensen Newtec, Stærmosegårdsvej 18, Odense, Denmark Soeren.staerke@newtec.dk Abstract Diffusion-assisted synthesis (DAS) is a gentle, transfer-free and potentially inexpensive method for forming graphene and carbonaceous thin films at low temperatures (< 200 °C). One of the main advantages of DAS is that it is independent of the substrates morphology and chemical composition. DAS can therefore be used to form graphene on even complex and insulating surfaces. DAS was first described in 2012 by Kwak et al. [1]. The principle of DAS is to deposit a few hundred nm thick porous metal film on a substrate. A carbonaceous paste is then placed on top of the porous metal film and the sample is heated. Finally the carbon pasta and the metal film is dissolved leaving a layer of graphene or multilayer graphene on the substrate (Figure 1). Newtec has under ambient conditions obtained experimental evidence for the formation of graphene by DAS at room temperature. The use of photolithography to control the structuring of the initial metal film in order to pattern the final graphene layer for direct printing of electrical circuits is also at present been investigated by Newtec. References [1] Jinsung Kwak, Jae Hwan Chu, Jae-Kyung Choi, Soon-Dong Park, Heungseok Go, Sung Youb Kim, Kibog Park, Sung-Dae Kim, Young-Woon Kim, Euijoon Yoon, Suneel Kodambaka & Soon-Yong Kwon, Near room-temperature synthesis of transfer-free graphene films. Nature Communications 3, Article number 645, Published 24 January 2012. Figures

A diagram of the basic procedure in DAS. A) A nickel thin film is deposited on the substrate and a carbonaceous paste is afterwards applied on top. B) The sample is heated for a short period to enhance diffusion. C) The paste and Ni film is removed by etching (FeCl 3) leaving the substrate with the graphene film on top.


Highly Sensitive and Selective SPR Biosensing Using Graphene Oxide Yury Stebunov, Aleksey Arsenin Laboratory of Nanooptics and Plasmonics, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russian Federation ystebunov@gmail.com The last few years the growing branch of the graphene research has focused on the properties and applications of graphene oxide (GO). Graphene oxide exhibits excellent properties such as unique mechanical and thermal behavior, water solubility, a simple method of synthesis, a possibility of chemical or thermal reduction, a simple film deposition process, and conjugation with a variety of biomolecules [1]. All these features make GO a promising candidate for biosensing. Also graphene oxide films have the large surface area, which provides more surface sites for adsorption of biomolecules. So we proposed the biosensor chip based on the thin graphene oxide films for the highly sensitive and specific biosensing using surface plasmon resonance technique. Surface plasmon resonance biosensing is a powerful instrument for the label-free biosensing, which allows not only to detect the presence of specific molecules in the test solution, but also to study the kinetics of biochemical reactions. Recently several papers were published about the graphene using for SPR biosensing. When graphene was used as a substrate for biomolecules adsorption, the adsorption capacity of proposed scheme was higher than for the thiol-functionalized surface widely used for SPR biosensing [2]. But the described biosensing scheme is non-specific which means that the molecules of different types presenting in the fluid sample can be adsorbed on the graphene surface. Also several papers were published about the influence of graphene on the distribution of the surface plasmon field near the metal film. It was obtained that thin graphene layers deposited on the surface of metal film could improve the sensitivity of SPR biosensing and the increase in the sensitivity is proportional to the number of graphene layers [3-4]. Figure 1 outlines the manufacturing process of the sensor chip intended for biosensing of oligonucleotide sequences. The surface plasmons are excited at the interference between metal films and dielectric media, for our experiments we used the 40 nm thick gold film with 2 nm Ti underlayer deposited on the borosilicate glass. The next step is the deposition of the thin graphene oxide film on the surface of metal. The graphene oxide is deposited from the aqueous solution using the spray-coating technique with the GO flake mean size of about 0.5-1 um. After that the layer of streptavidin molecules was created on the surface of the graphene oxide film. The 100 ug/ml streptavidin solution in 10 mM sodium acetate buffer was injected in the flow cell for 7 min. After streptavidin injection the solution of 200 nM biotinylated oligos in PBS buffer was injected for about 5 min, and due to the biotin-streptavdin interaction the layer of biotinylated oligos was formed. The last stage is an injection of the test solution containing the target oligos, the detection is based on the fact that target oligos interact with the complementary biotinylated oligos. It worth noting that during the processes of the biotinylated oligos and target oligos depositions other molecules do not interact with the surface of the sensor chip which is explained by the uniformity of the streptavidin layer formed on the surface of graphene oxide. Figure 2 illustrates the amount of the biotinylated oligos adsorbed on the surface of the graphene oxide based sensor chip and on the surface of the biochip based on the 150 nm thick layer of the carboxymethylated dextran. In the case of the GO sensor biochip 30% more oligos adsorbed showing the increase in biosensing sensitivity. In conclusion we proposed the novel sensor chip for SPR biosensing based on the graphene oxide. It shows the increased sensitivity of biosensing compared to the conventional SPR sensor chips based on the self-assembled monolayers of alkanethiolates and the hydrogel layers. Graphene oxide is an excellent choice for using as a linking layer between metal film and layers of biomolecules in SPR sensor chips due to the possibility to create highly selective sensing surface of various types of biomolecules. High bioreactivity of graphene oxide is explained by the mechanism of pi-stacking interaction of GO with almost all types of biomolecules [5]. Also deposition of the biomolecules on the surface of the graphene oxide films is realized without using of any activation process required in the cases of hydrogels and selfassembled monolayers of alkanethiolates. Furthermore GO films deposited on the surface of the metal are stable and could protect the surface of the metal film. It allows us to design biosensing schemes based on the silver films instead of the gold ones, because of silver shows better plasmonic properties [6], but it is too reactive at ambient conditions.


References [1] O.C. Compton and S. T. Nguyen, Small, 6 (2010) 711-723. [2] E. Wijaya, N. Maalouli, R. Boukherroub, S. Szunerits, J-P. Vilcot, Proc. of SPIE, 8424 (2012). [3] L. Wu, H. S. Chu, W. S. Koh, and E. P. Li, Optics Express, 18 (2010). [4] Md.S. Islam, A.Z. Kouzani, X.J. Dai, W.P. Michalski, and H. Gholamhosseini, Journal of Biomedical Technology, 8 (2012) 380-393. [5] Y. Wang, Z. Li, J. Wang, J. Li, and Y. Lin, Trends in Biotechnology, 29 (2011) 205-212. [6] S.H. Choi, Y.L. Kim, and K.M. Byun, Optics Express 19 (2011). Figures

Figure 1. Scheme of the manufacturing process of the SPR sensor chip intended for the sensing of oligonucleotide sequences.

Figure 2. The kinetics curves of the biotinylated oligos adsorption on (a) the graphene oxide based sensor chip and on (b) the sensor chip based on the carboxymethylated dextran.


Material Platform for the Manufacturing of Multifunctional Graphene Sheets Karlheinz Strobl, Riju Singhal, Mathieu Monville CVD Equipment Corporation, 355 South Technology Drive, Central Islip NY11722, U.S.A kstrobl@cvdequipment.com Abstract Graphene, in its one atom thick carbon sheet form, is a special 2 dimensional nanomaterial that bridges the chemical and physical worlds. On the one hand, graphene can be seen as a chemical, a gigantic two-dimensional monomer, allowing organic chemistry to investigate its use as a reactive platform and composite and polymer science to investigate its functionalized forms into dispersed, percolated or continuous architectures, ranging from randomly to highly organized structures. On the other hand, its intrinsic physical properties span from high electron mobility, exceptional mechanical strength to high surface area among others. All these variations can provide novel opportunities for designing new devices or materials with enhanced properties in electronics, spintronics, thermal management, energy generation and storage, composite material, biotechnology, etc. [1,2] Many manufacturing routes of graphene or graphene-like and/or nanocarbon materials have been published in the recent years. With each manufacturing process leading to a particular carbon-based nanomaterial one can see a growing availability of nanocarbon materials that can potentially provide unique benefits in selected applications. CVD Equipment Corporation has recently developed a novel and flexible NanotoMarcoâ&#x201E;˘ manufacturing process that allows us to transform graphene or graphenelike nano-powders into macroscopic forms. More specifically we can transform them into flexible sheets with controlled electrical and/or thermal conductivity, mechanical strength, porosity, thickness, anisotropic behavior, etc. This allow us to optimize their value proposition for a given target application. We believe this approach ensures an easy and safe handling of these nanomaterials while providing more value added opportunities for them. In this paper we present the first series of measurement performed on a variety of graphene-like powdery starting materials transformed into a sheet format with our proprietary NanotoMarcoâ&#x201E;˘ manufacturing process. In particular we will focus on the electrical and electrochemical properties of the resulting composite papers.

References [1] Z. Sun , D. K. James , J. M. Tour, J. Phys. Chem. Lett. 2 (2011), 2425-2432. [2] W. Wei, X.Qu, Small 8 (2012), 2138-2151.

Figures

Fig.1. two samples of paper-like nanocarbon sheet created through our NanotoMarcoâ&#x201E;˘ manufacturing process. Final properties depend on the type of nanocarbons used as raw materials and on the chosen manufacturing process steps (measuring tape in inches).


Graphene on Ir/YSZ/Si(111): low-cost synthesis and electronic properties 1

2

3

4

5

5

C. Struzzi , A.V. Fedorov , N.I. Verbitskiy , A. Nefedov , J. Gärtner , W. Weber , 6 7 7 7 7 7 H. Sachdev , M. Scardamaglia , P. Gargiani , S. Lisi , M.G. Betti , C. Mariani , 8 8 8 2,3 1 M. Schreck , S. Gsell , Ch Wöll , A. Grüneis , L. Petaccia 1

Elettra Sincrotrone Trieste, Strada Statale 14 km 163.5, 34149 Trieste, Italy 2 IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany 3 4 Faculty of Physics, University of Vienna, A-1090 Vienna, Austria- Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany 5 Namlab gGmbH, Noethnitzer Str. 64, 01187 Dresden, Germany 6 Max Planck Institute for Polymer Research, D-55128 Mainz, Germany 7 Dept. of Physics, University of Rome "La Sapienza", I-00185, Rome, Italy 8 Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany

Abstract Graphene is seen as potential successor to silicon [1,2] due to its high charge carrier mobility, which could facilitate ultra high speed electronic devices. Chemical vapour deposition (CVD) synthesis of graphene on single crystal metal surfaces [3] represents a widely used approach, which offers scalable methods for the large-scale production of high-quality graphene layer but it is severely limited by the high cost. The scalable approach of graphene formation reported here provides an important route to the low cost mass production of epitaxial graphene on silicon-based multilayer substrates, which are already available in 4-inch wafers [4]. We have investigated the selective formation of graphene on single crystal Ir(111) films, grown heteroepitaxially on Si(111) wafers with yttria stabilized zirconia (YSZ) buffer layers, using several hydrocarbons and substrate temperatures during CVD synthesis. This surface-induced chemical growth mechanism has been investigated using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorpion fine structure (NEXAFS), and angle-resolved photoemission spectroscopy (ARPES), showing that monolayer graphene grown on Ir(111) films on YSZ/Si(111) is comparable in surface quality to graphene/Ir(111) bulk single crystals and it represents a good way for an up-scalable and low cost synthesis of graphene. Using higher CVD temperatures, ARPES clearly shows double bands characteristic of bilayer graphene formation. References [1] K. S. Novoselov, A. K. Geim, et al., Science, 306, 666 (2004) [2] C. Berger, Z. Song, et al., Science, 312, 1191 (2006) [3] J. Wintterlin, M.L. Bocquet, Surface Science, 603, 1841 (2009) [4] S. Gsell, M. Fischer, et al., Applied Physics Letters, 91, 061501 (2007)


Figure: ARPES map of monolayer graphene on Ir(111)/YSZ/Si(111), acquired at RT, using 34 eV photon energy and horizontal polarization.


Covalent Functionalization of Graphene Oxide via a Chemical and Photochemical Method for Organic Photovoltaic Applications 1

Minas M. Stylianakis, Emmanuel Stratakis,

1,2

Emmanuel Kymakis

1

1

Center of Materials Technology & Photonics, Technological Educational Institute (TEI) of Crete, Heraklion 71004 Crete, Greece; 2 Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), Heraklion, 71110 Crete, Greece; stylianakis@staff.teicrete.gr Abstract: Natural graphite powder was oxidized by Hummersâ&#x20AC;&#x2122; method and graphite oxide was prepared [1]. After ultrasonication was expanded, in order to exfoliate single or/and few layered graphene oxide sheets (GO). Although, the quite low solubility of GO, which is a very important factor in organic photovoltaics, blocks the formation of stable suspensions, as well as solutions, for the exploitation of its unique mechanical properties. In this study, we report our recent results on the covalent functionalization of graphene oxide via a chemical and photochemical method; the addition of an aliphatic amine group linked with a small molecule is demonstrated to increase the dispersability of chemically and photochemically functionalized graphene oxide in organic solvents, so that to synthesize new electron acceptors, appropriate for organic photovoltaics, based on heterostructure polymer-graphene composite layers. In particular, the carboxyl groups of GO are activated using thionyl chloride (SOCl2) and finally are coupled with 3,5-dinitrobenzoyl chloride (DNBC) by using 1,4-ethylenediamine as ligament. The above coupling reaction was performed by chemical, as well as by photochemical way, yielded GOEDNB and LGO-EDNB, respectively. The photochemical method for the simultaneous functionalization of GO was held through pulsed UV laser irradiation of GO in liquid precursor media [2]. Using this technique we have successfully synthesized GO-ethylene dinitrobenzoyl (EDNB) at room temperature in less than 2 hours, compared to 3 days required upon using a conventional chemical route [3]. GOEDNB and LGO-EDNB derivatives were used as the electron acceptor materials in poly-(3hexylthiophene) (P3HT) bulk heterojunction photovoltaic devices to significantly enhance the performance, yielding a power conversion efficiency improvement of two orders and one order of magnitude compared with the pristine P3HT and the P3HT-GO devices respectively. References [1] William S. Hummers Jr., Richard E. Offeman, J. Am. Chem. Soc., 80 (1958) 1339. [2] Minas M. Stylianakis, Kyriaki Savva, Emmanuel Kymakis, Emmanuel Stratakis, Submitted. [3] Minas M. Stylianakis, George D. Spyropoulos, Emmanuel Stratakis, Emmanuel Kymakis, Carbon, 50 (2012) 5554. Figures

Figure 1. The chemical functionalization of GO


UV Laser

Figure 2. The photochemical functionalization of GO


Flexible free-standing hollow Fe3O4/graphene hybrid films for lithium-ion batteries

Jing Sun, Ronghua Wang, Chaohe Xu, Lian Gao Shanghai Institute of Ceramics, 1295 Dingxi Road, Shanghai, China jingsun@mail.sic.ac.cn Abstract Flexible free-standing hollow Fe3O4/graphene (H- Fe3O4/GS) films were fabricated through vacuum filtration and thermal reduction process, in which graphene formed a three-dimensional conductive network, with hollow and porous Fe3O4 spindles being captured and distributed homogeneously. Using the films as binder-free and free-standing electrode for lithium-ion batteries, H- Fe3O4/GS with 39.6 wt% graphene exhibited a high specific capacity (1555 mAh g-1 at 100 mA g-1), enhanced rate capability and excellent cyclic stability (940 and 660 mAh g-1 at 200 and 500 mA g-1 after 50 cycles, respectively). The superior electrochemical performance of this novel material can be attributed to two reasons. One is three dimensional (3D) graphene network formed is very helpful to keep H- Fe3O4 in good electric contact. Another is the short transport length for both lithium ions and electrons, porous nature to accommodate volume change and favor electrolyte penetration. It is believed that the strategy for preparing free-standing H- Fe3O4/GS papers presented in the work will provide new insight into the design and synthesis of other metal oxide/GS electrodes for flexible energy storage devices.

References 1. E. Kang, Y. S. Jung, A. S. Cavanagh, G. H. Kim, S. M. George, A. C. Dillon, J. K. Kim and J. Lee, Advanced Functional Materials, 2011, 21, 2430-2438. 2. W. M. Zhang, X. L. Wu, J. S. Hu, Y. G. Guo and L. J. Wan, Advanced Functional Materials, 2008, 18, 3941-3946. 3. Y. Chen, H. Xia, L. Lu and J. M. Xue, Journal of Materials Chemistry, 2012, 22, 5006-5012. 4. RonghuaWang, Chaohe Xu, Jing Sun, Lian Gao, Chucheng Lin, Journal of Materials Chemistry C, 2013, 1, 1794-1800

Figures

Synthesis of Fe3O4/graphene and their electrochemical properties


1

Light emission and detection in single layer MoS2 1

2

1

1

3

4

4

R. S. Sundaram , A. Lombardo , M. Engel , A.L. Eiden , U.Sassi ,R.Krupke , Ph. Avouris , M. Steiner , 1 A.C. Ferrari . 1

Cambridge Graphene Centre, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom 2 Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany 3 Institut f체r Materialwissenschaft, Technische Universit채t Darmstadt, 64287 Darmstadt, Germany 4 IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA rss55@cam.ac.uk

Abstract Molybdenum disulphide (MoS2), a layered quasi-2 dimensional (2d) chalcogenide material[1-3], is subject of intense research because of its electronic[4] and optical properties[5], such as strong photoluminescence (PL)[5, 6], controllable valley and spin polarization[7, 8]and a large on-off ratio in field effect transistors (FETs)[4]. This combination of electrical and optical properties suggests that 1LMoS2 is a promising candidate for novel optoelectronic devices, such as 2d photodetectors[9, 10], and light-emitting devices. Here, we study photodetectors fabricated based on 1L-MoS2[11]. Using spatially resolved photocurrent measurements we characterize the active areas of photodetection. Devices fabricated with Au source and drain electrodes show zero net photocurrent under zero bias conditions with charge separation occurring in the vicinity of the contacts. However, a strong built-in potential within the channel is observed in devices fabricated with asymmetric drain-source contacts using thermally evaporated Au and Pt. This results in a net photocurrent at zero bias. Furthermore, we exploit the direct band gap of 1L-MoS2 to demonstrate electrically excited luminescence in devices made of 1L-MoS2 and study the underlying emission mechanism. We find that the electroluminescence occurs via hot carrier processes and is localized in the region of the contacts(figure 1a). The observed photoluminescence and electroluminescence arise from the same excited state at 1.8eV(figure 1b) References [1] R. F. Frindt, J. Appl. Phys. ,37, 1928 (1966).. [2] X. Zhang, W. P. Han, J. B. Wu, S. Milana, Y. Lu, Q. Q. Li, A. C. Ferrari, P. H. Tan; arXiv:1212.6796 (2012) [3] F. Bonaccorso, A. Lombardo, T. Hasan, Z. Sun, L. Colombo, A. C. Ferrari; Materials Today 15, 564 (2012) [4] Radisavljevic B., Radenovic A., Brivio J., Giacometti V., and Kis A., Nature Nano 6, 147 (2011).. [5] K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Phys. Rev. Lett., 105, 136805 (2010). [6] A. Splendiani, L. Sun, Y. Zhang, T. Li, J. Kim, C.-Y. Chim, G. Galli, and F. Wang, Nano Lett., 10, 1271 (2010). [7] K. F. Mak, K. He, J. Shan, and T. F. Heinz, Nature Nano, 7, 494 (2012). [8] H. Zeng, J. Dai, W. Yao, D. Xiao, and X. Cui, Nature Nano, 7, 490 (2012). [9] Yin, Z.; Li, H.; Li, H.; Jiang, L.; Shi, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H. ACS Nano, 6, 74 (2011). [10] H. S. Lee, S.-W. Min, Y.-G. Chang, M. K. Park, T. Nam, H. Kim, J. H. Kim, S. Ryu, and S. Im, Nano Letters 12, 3695 (2012). [11] R. S. Sundaram, M. Engel, A. Lombardo, R. Krupke, A. C. Ferrari, Ph. Avouris, M. Steiner; arXiv:1211.4311 (2012) Figure

a)


Figure 1. (a) False color image showing EL emission in the vicinity of a contact edge. The positions of Cr/Au contacts are highlighted by thick dashed lines (white) and the MoS2 layer is indicated by thin dashed lines (grey). Absorption (Abs), EL, and PL spectra on the same 1L-MoS2.


The correlation between the growth temperature of graphene deposited on the 3C-SiC/Si template substrates and the quality of the obtained layers Dominika Teklinska

12

, Kacper Grodecki

13

1

, Wlodek Strupinski , Andrzej Olszyna

2

1) Institute of Electronic Materials Technology, 133 Wolczynska Street, 01-919 Warsaw, Poland, 2) Warsaw University of Technology, Faculty of Materials Science, 141 Woloska Street, 02-507 Warsaw, Poland, 3) Institute of Experimental Physics, Faculty of Physics, University of Warsaw, 69 Hoza Street, 00-681 Warsaw, Poland, dominika.teklinska@itme.edu.pl Abstract Epitaxial graphene is a new material composed of one or more two-dimensional sheets of carbon atoms in which each carbon atom is covalently bound to its 3 neighbors (sp2 bonds) to form a honeycomb structure. It can be grown on many silicon carbide polytypes such as 6H [1], 4H [2] and 3C [3]. However, the high cost of hexagonal SiC substrates is a major hindrance to the application of graphene on SiC. Moreover, silicon carbide substrates have a limited diameter (up to 6”), unlike silicon substrates, the diameter of which is even up to 18”. To overcome all these problems we have been investigating the use of a 3C-SiC thin carbonization layer on silicon substrates as a template substrate for graphene epitaxy. Such a graphene layer offers excellent potential for obtaining graphene films on large-area silicon wafers. Moreover, such an epitaxial structure is compatible with silicon technology. Firstly, the deposition of the 3C-SiC carbonization layer on the silicon substrate has to be performed using a resistively heated hot-wall Chemical Vapor Deposition reactor. The 3C-SiC carbonization layer is formed while silicon atoms which out-diffuse from the substrate react with carbon atoms from the precursor in appropriate growth conditions. Growth of the SiC layer is self-regulated due to the limitation of Si out-diffusion and carbon-in-diffusion at a given temperature [4]. 3C-SiC formed on the Si substrate is not used as a layer that is self-converted into graphene by sublimation but rather as a template for graphene growth. In the next step, the graphene layer on the silicon carbide substrate is obtained. To sum up, we could divide the growth process into two parts. At first, there is growth of the 3C-SiC carbonization layer and subsequently the deposition of graphene. We investigate the influence of the process growth temperature (1050°C, 1200°C, 1250°C and 1300°C) of the graphene layer on its crystalline quality. From our experiments, an appropriate value of the temperature of the deposition of the graphene layer is 1250°C. Each of the sets of the samples grown with the graphene layer in different thermal conditions is subject to characterization using two methods. Atomic Force Microscopy measurements allow determination of the influence of the process temperature on the morphology of the surface of graphene. Based on Raman Spectroscopy measurements we assess the quality of the obtained graphene layers. References [1] K.V. Emtsev, A. Bostwick, K. Horn, J. Jobst, G.L. Kellogg, L. Ley, J.L. McChesney, T. Ohta, S.A. Reshanov, J. Rohrl, E. Rotenberg, A.K. Schmid, D. Waldmann, H.B. Weber, T. Seyller, Nat. Mater. 8 (2009) 203. [2] C. Berger, Z.M. Song, X.B. Li, X.S. Wu, N. Brown, C. Naud, D. Mayo, T.B. Li, J. Hass, A.N. Marchenkov, E.H. Conrad, P.N. First, W.A. de Heer, Science 312 (2006) 1191. [3] V.Y. Aristov, G. Urbanik, K. Kummer, D.V. Vyalikh, O.V. Molodtsova, A.B. Preobrajenski, A.A. Zakharov, C. Hess, T. Hänke, B. Büchner, I. Vobornik, J. Fujii, G. Panaccione, Y.A. Ossipyan, M. Knupfer, Nano Lett. 10 (2010) 992. [4] A. Addamiano, J.A. Sprague, Appl. Phys. Lett. 44 (1984) 525.


Graphene-based Materials for Supercapacitor Applications 1

1

1

1

C. Trapalis , E. Vermisoglou , N. Todorova , T. Giannakopoulou , G. Romanos 2 2 2 F. Markoulidis , E. Lei , C. Lekakou

1

1

Institute of Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, NCSR “Demokritos”, 153 10, Ag. Paraskevi, Attikis, Greece 2 Division of Mechanical, Medical, and Aerospace Engineering, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK trapalis@ims.demokritos.gr Abstract High quality graphene sheets with superior physical properties such as large surface area and high electrical conductivity allowed the development of new engineered carbons for energy storage devices. Towards this goal, high surface area graphene oxide materials were prepared using various pristine graphite and oxidation methods. Natural graphite with different sizes and microwave expanded graphite were oxidized using modified Staudemayer or Hammers methods. The resulting graphite oxide paper was exfoliated and reduced via microwave treatment leading to few layers graphene/graphene oxide nanostructures (EGO). Impregnation in KOH and high temperature treatment in vacuum was also applied to increase the porosity and diminish the oxygen content in the final materials (t-EGO). The obtained materials were further processed to create metal and metal oxide/graphene heterostructures [1, 2]. Graphene-based materials were either decorated with silver (Ag) nanoparticles or intercalated with iron carbide (Fe3C) nanostructures. The structural, morphological and electrical properties of the bare and composite graphitic materials were investigated. The XRD and TEM analysis confirmed the oxidation of graphite and further exfoliation to few layers graphene, respectively. It was also established that the oxidation route and especially the type of the pristine graphite (flake size, pretreatment) influence significantly the level of oxidation, the specific surface area and the electrical properties of the produced graphene. Liquid N2 adsorption-desorption isotherms demonstrated that small flakes (100 mesh) natural graphite and 2 2 expanded graphite resulted in large specific surface area (>900 m /g up to ~2400 m /g) of the prepared EGO. The use of larger flakes (10 mesh) natural graphite led to lower BET surface but higher capacitance (~629 F/g) assessed by CV measurements. The Raman results revealed that KOH acted more as a reducing agent diminishing the defects than as surface modifier for high porosity. It was also established that the decoration of EGO and t-EGO with Ag nanoparticles (~40 nm) trough photodeposition decreased the structural defects of the graphene. However, the procedure did not improve the capacitance of the resulting materials. The activated t-EGO/Ag composite exhibited supercapacitor’s behavior with lower capacitance than the bare graphene, while the non-activated EGO/Ag acted as a resistant. The outcome was related with the deposition of Ag not between but onto the surface and the edges of the graphene layers and the decrease of the materials porosity. In the case of graphene oxide/Fe3C hybrids it was established that the immobilization of Fe-based intercalant (IFe) was governed by the pH of the aqueous graphite oxide dispersion following nucleophilic substitution or ion exchange path. Subsequent thermal annealing resulted in formation of pillaring Fe3C nanoparticles encapsulated in a graphite shell. It is suggested that the graphite shell prevent the aggregation between both adjacent Fe3C nanoparticles, and bundles of neighboring multi-layer graphenes. The exhibited properties of the obtained hybrid materials make them appropriate for magnetic and supercapacitor applications. These materials have also the advantage of being low cost, low toxicity and environmentally friendly.

References [1] E. Vermisoglou, N. Todorova, G. Pilatos, G. Romanos, V. Likodimos, N. Boukos, C. Lei, F. TH Markoulidis, C. Lekakou, C. Trapalis, ECCM15 - 15 European Conference on Composite Materials, Venice, Italy, 24-28 June 2012. [2] J. Zhu, M. Chen, H. Qu, Zh. Luo, Sh. Wu, H. A. Colorado, S. Wei, and Zh. Guo, Energy Environ. Sci., 6 (2013) 194.


Process of strain relief in large area graphene Gerald V. Troppenz, Marc A. Gluba, Marco Kraft, Jörg Rappich, Norbert H. Nickel Helmholtz-Zentrum für Materialien und Energie GmbH, Kekuléstr. 5, 12489 Berlin, Germany gerald.troppenz@helmholtz-berlin.de Abstract In graphene biaxial compressive strain accumulates during the chemical vapor deposition 1-3 (CVD) due to a mismatch of the thermal expansion coefficient of copper substrates and graphene. Here, we show experimentally that this strain is released in three successive steps. (i) Initially during cool-down from the growth temperature graphene causes a corrugation of the Cu surface (see Fig.1). We demonstrate that the restructuring of the Cu surface is driven by strain due to the presence of graphene. Moreover, this leads to an increase of the graphene area by about 1%. (ii) in-situ Raman measurements reveal that the removal of the Cu substrate causes a significant strain relaxation, and (iii) additional strain is relieved when graphene is transferred to SiO2 substrates. We quantify the amount of strain which relaxes during each step and deduce the residual strain remaining in transferred graphene. References [1] He, R.; Zhao, L.; Petrone, N.; Kim, K. S.; Roth, M.; Hone, J.; Kim, P.; Pasupathy, A.; Pinczuk, A. Nano Lett. 2012, 12, 2408–2413. [2] N’Diaye, A. T.; Gastel, R. van; Martínez-Galera, A. J.; Coraux, J.; Hattab, H.; Wall, D.; Heringdorf, F.J. M. zu; Hoegen, M. H.; Gómez-Rodríguez, J. M.; Poelsema, B. New Journal of Physics 2009, 11, 113056. [3] Hattab, H.; N’Diaye, A. T.; Wall, D.; Klein, C.; Jnawali, G.; Coraux, J.; Busse, C.; Gastel, R. van; Poelsema, B.; Michely, T. et al. Nano Lett. 2012, 12, 678–682. Figures

Figure 1. Atomic force microscopy micrographs of copper (a) with and (b) without the growth of graphene. Note that sample (a) underwent the same process as (b) just without CH4 flow. (c) shows line scans of the corresponding surfaces depicted in (a) and (b).


Two Graphene Mechanical Resonators Coupled by a Nanotube Beam 1,2

Ioannis Tsioutsios,

1,2

Joel Moser,

3

José Antonio Plaza, Adrian Bachtold

1,2

1- ICFO, Av. Carl Friedrich Gauss, 08860 Castelldefels, Barcelona, Spain 2- ICN, CIN2-CSIC, Campus UAB, 08193 Barcelona, Spain 3- IMB-CNM (CSIC), E-08193 Bellaterra, Barcelona, Spain ioannis.tsioutsios@icfo.es Abstract Mechanical resonators can be coupled [1] in order to create new systems featuring a rich variety of nonlinear dynamics. These nonlinearities give rise to interesting behaviors, such as vibration localization [2], synchronization [3], chaos [4], and parametric mode splitting [5]. Furthermore, coupled mechanical resonators also offer new strategies to improve the quality factor [6], as well as to detect charge [7] and mass [8] with high sensitivity. These devices have been fabricated from metallic and silicon-based materials using top-down micromachining. Alternate materials endowed with interesting mechanical properties are carbon nanotubes and graphene. A nanotube is a one-dimensional wire whose diameter can be as low as 1 nm, and graphene is a one-atom thick, two-dimensional sheet. Single mechanical resonators based on individual nanotubes and graphene sheets have been fabricated [9,10,11,12,13,14]. These resonators possess a wide variety of useful properties: they can be employed as sensitive mass detectors [15], their resonance frequency can be above 10 GHz [16], they exhibit strong mechanical nonlinearities [14], and their mechanical vibrations can efficiently couple to electrons in the Coulomb blockade and the quantum Hall regimes [10,11,17]. The coupling between two vibrating nanotubes has been studied by gluing several nanotubes on a tip and by imaging them in a transmission electron microscope [18]. However, because nanotubes and graphene cannot be structured as easily as other materials, it has not been possible to use them as building blocks to create coupled resonator devices. In this work, we demonstrate a multi-element resonant structure consisting of two graphene plates linked by a nanotube beam (Fig. 1). Each graphene plate is clamped by two metal electrodes, so that mechanical vibrations can be both actuated and detected electrically using the mixing technique [9,19]. Two mechanical eigenmodes are measured, each corresponding to vibrations localized in a different graphene plate. The coupling between the eigenmodes is evaluated by measuring the shift of the resonance frequency of one graphene plate as a function of the estimated vibration amplitude of the other plate (Fig. 2).

References [1] E. Buks, and M. L. Roukes, J. MEMS, 11 (2012) 802. [2] M. Sato, B. E. Hubbard, and A. J. Sievers, Phys. Rev. Lett., 90 (2003) 044102. [3] M. C. Cross, A. Zumdieck, R. Lifshitz, and J. L. Rogers, Phys. Rev. Lett., 93 (2004) 224101. [4] R. B. Karabalin, M. C. Cross, and M. L. Roukes, Phys. Rev. B, 79 (2009) 165309. [5] H. Okamoto, A. Gourgout, C. Y. Chang, K. Onomitsu, I. Mahboob, E. Y. Chang, and H. Yamaguchi, arXiv, 1212.3097 (2012). [6] Y. W. Lin, L. W. Hung, S. S. Li, Z. Ren, and C. T. -C. Nguyen, in Quality factor boosting via th mechanically-coupled arraying: Proceedings of the 4 International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS and EUROSENSORS, Lyon, France, 10-14 June (2007) 2453-2456. [7] R. B. Karabalin, R. Lifshitz, M. C. Cross, M. H. Matheny, S. C. Masmanidis, and M. L. Roukes, Phys. Rev. Lett., 106 (2011) 094102. [8] E. Gil-Santos, D. Ramos, A. Jana, M. Calleja, A. Raman, and J. Tamayo, Nano Lett., 9 (2009) 41224127. [9] V. Sazonova, Y. Yaish, H. Üstünel, D. Roundy, T. A. Arias, and P. L. McEuen, Nature, 431 (2004) 284-287. [10] B. Lassagne, Y. Tarakanov, J. Kinaret, D. Garcia-Sanchez, and A. Bachtold, Science, 325 (2009) 1107-1110.


[11] G. A. Steele, A. K. H端ttel, B. Witkamp, M. Poot, H. B. Meerwaldt, L. P. Kouwenhoven, and H. S. J. van der Zant, Science, 325 (2009) 1103-1107. [12] J. S. Bunch, A. M. van der Zande, S. S. Verbridge, I. W. Frank, D. M. Tanembaum, J. M. Parpia, H. G. Craighead, and P. L. McEuen, Science, 315 (2007) 490-493. [13] C. Chen, S. Rosenblatt, K. I. Bolotin, W. Kalb, P. Kim, I. Kymissis, H. L. Stormer, T. F. Heinz, and J. Hone, Nature Nanotech., 4 (2009) 861-867. [14] A. Eichler, J. Moser, J. Chaste, M. Zdrojek, I. Wilson-Rae, and A. Bachtold, Nature Nanotech., 6 (2011) 339-342. [15] J. Chaste, A. Eichler, J. Moser, G. Ceballos, R. Rurali, and A. Bachtold, Nature Nanotech., 7 (2012) 301-304. [16] J. Chaste, M. Sledzinska, M. Zdrojek, J. Moser, and A. Bachtold, Appl. Phys. Lett., 99 (2011) 213502. [17] V. Singh, B. Irfan, G. Subramanian, H. S. Solanki, S. Sengupta, S. Dubey, A. Kumar, S. Ramakrishnan, and M. M. Deshmukh, Appl. Phys. Lett., 100 (2012) 233103. [18] S. Perisanu, T. Barois, P. Poncharal, T. Gaillard, A. Ayari, S. T. Purcell, and P. Vincent, Appl. Phys. Lett., 98 (2011) 063110. [19] V. Gouttenoire, T. Barois, S. Perisanu, J. L. Leclercq, S. T. Purcell, P. Vincent, and A. Ayari, Small, 6 (2010) 1060-1065.

Figure 1 (a) Atomic Force Microscopy image of the device before removing the substrate. (b) Scanning electron microscope image of the device at the end of the fabrication process.

Figure 2 Pump-probe experiment to study the coupling between the eigenmodes. (a) Resonance frequency of graphene plate 1 as a function of the frequency of the force applied to plate 2. The plot is obtained by continuously measuring the mixing current of plate 1 as a function of the frequency f1 of the probe force, while sweeping the frequency f2 of the pump force. (b) Setup of the measurement scheme. (c) Shift of the resonance frequency of plate 1 as a function of the pump voltage applied to plate 2.


Graphene as Reinforcement Filler in PMMA Nanocomposites 1

1

1

2

Cristina Valles , Ian A. Kinloch , Robert J. Young , Neil R. Wilson , Jonathan P. Rourke

3

1

2

School of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK 3 Department of Physics, and Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK cristina.valles@manchester.ac.uk

Graphene/polymer nanocomposites have been the focus of many investigations due to their exceptional thermal, mechanical and electrical properties. The exfoliation of graphite is the most promising route for producing graphene on the bulk scale for applications such as composites. Recently graphene oxide (GO) prepared using the Hummersâ&#x20AC;&#x2122; method [1] has been shown to be composed of functionalized graphene sheets decorated by strongly-bound oxidative debris acting as a surfactant that stabilizes aqueous GO suspensions [2]. These physi-absorbed aromatic acids can be removed by a simple NaOH(aq) wash to give base-washed GO (bwGO) reducing the oxygen content from 33% to < 20%, turning the hydrophilic nature of GO into hydrophobic, and improving the conductivity of films made from the material by 5 orders of magnitude [2]. The presence of these physi-absorbed groups on GO could potentially lower the Youngâ&#x20AC;&#x2122;s modulus of the flakes, as it turns the flake into a few-layer material, providing an easy shear plane between the debris, attached to the polymer. At the same time, such debris may improve the interface between the GO and matrix by acting as a compatibilising surfactant between polymer and filler. And they also may improve the dispersion of the graphene oxide in the polymer matrix, and hence the mechanical properties. Herein, we compare as-made and base-washed graphene oxide materials as reinforcing fillers in PMMA to establish the relative roles of the interface and GO modulus, and determine whether it is better to use as-made GO or base-washed, clean GO in nanocomposites. The nanocomposites were prepared at loadings from 0.5 to 10 wt.% by melt mixing using a twin-screw extruder. Gel permeation chromatography (GPC) and thermogravimetric analysis (TGA) were used to determine the structural properties of the matrix of the neat polymer and nanocomposites. Electrical measurements, dynamic mechanical thermal analysis (DMTA) and tensile testing were performed to study the electrical and mechanical properties of the nanocomposites, respectively, as a function of their structure, surface chemistry and dispersion in the polymer matrix. The nature of the interactions at the GO/bwGO-polymer interfaces were evaluated by Raman spectroscopy and related to the mechanical reinforcement of the nanocomposites observed upon the addition of the different types of GO.

References [1] W. S. Hummers, R. E. Offeman. J. Am. Chem. Soc., 80 (1958) 1339. [2] J. P. Rourke, P. A. Pandey, J. J. Moore, M. Bates, I. A. Kinloch, R. J. Young, N. R. Wilson. Angew. Chem. Int. Ed. 50 (2011) 3173.


Scaling Properties of Charge Transport in Polycrystalline Graphene Dinh Van Tuan1 , Jani Kotakoski2 , Thibaud Louvet1,3 , Frank Ortmann,1 , Jannik C. Meyer2 and Stephan Roche,1,4 1

CIN2 (ICN-CSIC) and Universitat Aut´ onoma de Barcelona, Catalan Institute of Nanotechnology, Campus UAB, 08193 Bellaterra, Spain 2 University of Vienna, Department of Physics, Boltzmanngasse 5, 1090 Wien, Austria 3 Ecole Normale Superieure de Lyon, 46, Allee d Italie, 69007 Lyon, France 4 ICREA, Instituci´ o Catalana de Recerca i Estudis Avan¸cats, 08070 Barcelona, Spain Contact: tuan.dinh@icn.cat

Abstract

Polycrystalline graphene is a patchwork of coalescing graphene grains of varying lattice orientations and size, resulting from the chemical vapor deposition (CVD)-growth at random nucleation sites on metallic substrates [1, 2, 3, 4, 5]. The morphology of polycrystalline graphene has become an important topic given its fundamental role in limiting the mobilities compared to mechanically exfoliated graphene monolayers [6]. The relationship between polycrystalline morphologies (grain sizes and grain boundary (GB) structures) and resulting physical properties is also a central aspect of the graphene roadmap in view of applications such as flexible electronics and high-frequency or spintronics devices [7]. Here we report new insights to the current understanding of charge transport in polycrystalline geometries. We first created realistic models of large CVD-grown graphene samples. Then, we used an efficient computational approach to compute charge mobilities within these systems as a function of the average grain size and the coalescence quality between the grains. Our results, which agree with recent experiments [8], reveal a remarkably simple scaling law for the mean free path and conductivity, correlated to atomic-scale charge density fluctuations (electron-hole puddles) along GBs. These findings establish quantitative foundations of transport features in polycrystalline graphene, thereby paving the way for improvements in graphene-based applications.

References [1] Li, X. S. et al., Science 324, 1312-1314 (2009). [2] Reina, A. et al., Nano Lett. 9, 30-35 (2009). [3] Bae, S. et al., Nature Nanotech. 5, 574-578 (2010). [4] Huang, P. Y. et al., Nature 469, 389-392 (2011). [5] Li, X. et al., J. Am. Chem. Soc. 133, 2816-2819 (2011). [6] Geim, A. K. & Novoselov, Nature Mater. 6, 183-191 (2007). [7] Novoselov, K.S, Falko, V.I., Colombo, L., Gellert, P.R., Schwab, M.G.,& Kim, K., Nature 192, 490 (2012). [8] A.W. Tsen et al., Science 336, 1143 (2012). [9] T.V. Dinh et al., Submitted to Nano Lett.

Figures

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b

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Figure 1: Polycrystalline graphene samples.

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0.14

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Figure 2: Density of states (DOS). a. DOS for pristine graphene (PG) and the structures presented in Fig. 1. b. Higher magnification of the DOS close to the charge neutrality point (E = 0, area marked with a rectangle in panel a). c. Atomic structure of one of the boundaries in sample “18 nm”, showing the electronhole puddles at GB sites that develop due to local variations in the charge density δi : local electron doping (δi < −1 × 10−4 e/atom) is shown in blue and local hole doping (δi > 1 × 10−4 e/atom) in red. d. Local DOS for atoms A1, A2 and A3 marked in panel c. e. Local DOS for atom A4 marked in panel c as compared to the average DOS for pristine graphene (PG) and average LDOS for all atoms at GBs in the same sample (GB). a

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Figure 3: Transport properties. a. Diffusion coefficient (D(t)) for the samples presented in Fig. 1. b. Mean free path ℓe (E) for equivalent structures with scaled ℓe (E) for samples with hdi ≈ 13 nm and hdi ≈ 25.5 nm, showing the scaling law. c. Semi-classical conductivity (σsc (E)) for all samples and as scaled for the same cases as above. d. Charge mobility (µ(E) = σsc (E)/en(E)) as a function of the carrier density n(E) in each of the RE samples (n(E) = 1/S 0 ρ(E)dE, S being a normalization factor).

2


Tunable magnetic contacts and their role in graphene spintronics I. J. Vera-Marun, P. J. Zomer, M. H. D. Guimarães, M. Wojtaszek, T. Maassen, and B. J. van Wees Physics of Nanodevices, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands i.j.vera.marun@rug.nl Abstract Graphene has proved to be an ideal system to study spin transport. However, graphene spintronic devices show spin relaxation lengths of up to a few micrometers at room temperature, orders of magnitude lower than theoretical predictions. Several works attribute this observation to the “conductivity mismatch” problem, where the difference between the spin resistance of the magnetic contact and the graphene channel causes injected spins to be backscattered into the contacts and therefore lose their spin information. A way to reduce this backscattering is by inserting an oxide barrier between the magnetic electrode and the graphene channel, resulting in highly resistive tunnel contacts. Here we approach this problem, both experimentally [1] and theoretically [2], in order to understand the experimental factors limiting the spin relaxation time in graphene. Our experimental approach focuses on harnessing the tunability of the magnetic contacts which control electrical spin injection and detection in graphene [1]. For this purpose we developed contacts where the oxidation state of the oxide barrier can be controlled by annealing or by electroforming. Both approaches result in tuning of the transport properties of the contacts via an increased contact resistance, appearance of tunneling behavior and even sign reversal of their spin polarization. This simple approach allows us to explore the graphene spin transport properties both with and without the conductivity mismatch problem within the same device. We also studied how nonlocal Hanle precession measurements are affected by the contact-induced spin relaxation via a spin transport model [2]. The model accounts for changes in the Hanle line shape due to the finite contact resistances and quantifies how it modifies the extracted spin transport properties. The combination of experiment and modeling allows us to conclude that the conductivity mismatch problem is not the limiting mechanism in the present experimental studies. Therefore we raise the need to uncover other sources of spin relaxation in graphene. References [1] I. J. Vera-Marun, P. J. Zomer, M. H. D. Guimarães, M. Wojtaszek, and B. J. van Wees, to be submitted. [2] T. Maassen, I. J. Vera-Marun, M. H. D. Guimarães, and B. J. van Wees, Phys. Rev. B, 86 (2012) 235408. Figures

Nonlocal Hanle precession in bilayer graphene, both before (left) and after (right) annealing. After annealing, we observe a threefold increase in the spin relaxation time and a sign reversal of the spin signals.


Graphene/polymer nanocomposites: thermoset and elastomer matrices Raquel Verdejo, Mario Martin-Gallego, Laura J. Romasanta, Marianella Hernández, M. Mar Bernal Miguel A. Lopez-Manchado Instituto de Ciencia y Tecnología de Polímeros, ICTP-CSIC, C/Juan de la Cierva, 3, 28006 Madrid, Spain r.verdejo@csic.es Abstract The addition of carbon nanotubes (CNT) to polymer matrices has already been shown to improve their mechanical, electrical and thermal properties. Although significant advances have been made in recent years, these tend to be modest compared to the theoretical performance due to unresolved processing issues. Hence, graphene sheets provide an alternative option to produce functional nanocomposites due to their excellent properties and the natural abundance of its precursor, graphite [1]. The purpose of the studies reported here was to investigate the inclusion of thermally exfoliated graphene (TRG) sheets in a range of polymer systems, both thermoset and elastomers (Figure), and to understand their effects on the curing, morphology and properties [2-10]. The graphene sheets used in these studies were synthesised in our laboratories from the thermal exfoliation and reduction of graphite oxide (GO). GO was produced using natural graphite powder (universal grade, 200-mesh, 99.9995%) according to the Brödie method. This method presents a lower disruption of the Csp2 graphitic structure than the Hummers method due to a lower oxidation degree, the oxygen contents by elemental analysis are 28% and 48%, respectively. The exfoliation was carried out at 1000 °C under inert atmosphere and did not completely remove the oxygencontaining groups (Figure). Both epoxy and polyurethane matrices have been studied analysing the effect on the curing kinetics and properties [6-10]. The inclusion of TRG did not did not raise the viscosity of both systems as much as CNT, maintaining the Newtonian behaviour even at 1.5 wt.-% in epoxy. Thus facilitating the processing of the curing materials. Both PU and epoxy resin presented an improved mechanical performance with the addition of TRG. The EMI shielding capabilities of TRG/PU foams were investigated in the X-band frequency region (8–12 GHz) observing an improvement of the specific EMI SE, from 7.6 to 15.15 dB cm 3/g with 0.3 wt.-% TRG. Silicones and natural rubber [2-5] showed a greater improvement in the mechanical performance than the thermoset matrices, with increments of up to 200 % in the compressive modulus of PDMS foams. TRG was studied as functional filler for the development of electromechanical actuators. We observed a ten-fold increase of the dielectric permittivity at low frequency for composites with 2.0 wt.% of TRG without the introduction of loss mechanisms.


The studies presented describe the successful production of thermoset and elastomer polymer nanocomposites with uniform dispersions of thermally exfoliated graphene. Generally, the inclusion of graphene sheets acted simultaneously as a reinforcing agent without adversely affecting processing. The different systems are especially interesting because of the widespread industrial application.

References [1] R. Verdejo, M. M. Bernal, L. J. Romasanta and M. A. Lopez-Manchado, J. Mater. Chem., 21, (2011), 3301. [2] R. Verdejo, F. Barroso-Bujans, M. A. Rodriguez-Perez, J. A. de Saja and M. A. Lopez-Manchado, J. Mater. Chem., 18, (2008), 2221. [3] R. Verdejo, C. Saiz-Arroyo, J. Carretero-Gonzalez, F. Barroso-Bujans, M. A. Rodriguez-Perez and M. A. Lopez-Manchado, Eur. Polym. J., 44, (2008), 2790. [4] L. J. Romasanta, M. Hernandez, M. A. Lopez-Manchado and R. Verdejo, Nanoscale Res. Lett., 6, (2011), 508: 1. [5] M. Hernandez, M. D. Bernal, R. Verdejo, T. A. Ezquerra and M. A. Lopez-Manchado, Compos. Sci. Technol., 73, (2012), 40. [6] M. Martin-Gallego, R. Verdejo, M. Khayet, J. M. O. d. Zarate, M. Essalhi and M. A. Lopez-Manchado, Nanoscale Research Letters, 6, (2011), 610: . [7] M. Martin-Gallego, R. Verdejo, M. A. Lopez-Manchado and M. Sangermano, Polymer, 52, (2011), 4664. [8] M. Martin-Gallego, M. Hernandez, V. Lorenzo, R. Verdejo, M. A. Lopez-Manchado and M. Sangermano, Polymer, 53, (2012), 1831. [9] M. M. Bernal, M. Martin-Gallego, L. J. Romasanta, A. C. Mortamet, M. A. Lopez-Manchado, A. J. Ryan and R. Verdejo, Polymer, 53, (2012), 4025. [10] M. M. Bernal, I. Molenberg, S. Estravis, M. A. Rodriguez-Perez, I. Huynen, M. A. Lopez-Manchado and R. Verdejo, J. Mater. Sci., 47, (2012), 5673.

Figure. (Left) Chart of Youngâ&#x20AC;&#x2122;s modulus as a function of density comparing graphene properties to 3 polymers and their composites.Graphene density was taken as 2200 kg/m . (Right) TEM image of thermally reduced graphene (TRG) showing its characteristic wrinkled structure.


Raman Spectroscopy of Ultra-Narrow Graphene Nanoribbons 1,†

2

1

3

3

3

I. A. Verzhbitskiy , P. May , P. Klar , A. Narita , X. Feng , K. Müllen , and C. Casiraghi

1,2,‡

1

Physics Department, Free University Berlin, Arnimalle 14, 14195 Berlin, Germany School of Chemistry, University of Manchester, Oxford road, M139PL Manchester, UK 3 Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany † ivan.verzhbitskiy@gmail.com ‡ cinzia.casiraghi@manchester.ac.uk 2

Abstract Graphene shows many outstanding properties [1], which make it suitable for a wide range of applications [2]. However, the lack of a band gap strongly affects the development of graphene-based field effect transistors. A simple method to open a gap is to use quantum confinement, i.e. to cut graphene into small stripes, called graphene nanoribbons (GNRs). The electronic properties of GNRs strongly depend on the width and on the atomic arrangement at the edges [3]. In particular, applications require ultra-narrow and well defined GNRs with perfect crystallographic edges. This is very difficult to achieve with the traditional top-down technology. Recent advances in bottom-up synthesis allowed production of GNRs of defined structure simply by sculpting the molecular precursor [4-6]. This opens a way to study narrow atomically-precise GNRs by optical means such as Raman spectroscopy. In this work we present a detailed multi-wavelength Raman analysis of bottom-up synthesized ultranarrow armchair GNRs (1-2nm in width) in powder. We also measured the precursors and the molecules synthesized from the original precursor during the GNRs synthesis. The first-order Raman spectrum of GNRs is dominated by two prominent peaks, namely the D and G peak. The G peak is blue-shifted and broadened as compared to graphene, due to quantum confinement. The intense D peak is activated by confinement of π-electrons into a finite-size graphitic -1 domain, similar to the band at around 1300 cm observed in Polycyclic Aromatic Hydrocarbons (PAHs) [7]. The D peak shows an interesting feature: depending on the excitation energy and power used, it splits into two components. Both the components follow the same vibration symmetry of the D peak. The Raman spectrum of GNRs also shows low energy modes similar to the Radial-Breathing Modes (RBMs) of CNTs. The measured frequencies of those peaks depend on the widths of the GNRs in good agreement with theoretical predictions [8]. This makes Raman spectroscopy a powerful technique to characterize GNRs in analogy to CNTs. References [1] K.S. Novoselov, Rev. Mod. Phys. 83 (2011) 837. [2] K.S. Novoselov et al., Nature 490 (2012) 192. [3] J.-C. Charlier et al., Top. Appl. Phys. 111 (2008) 673. [4] J. Cai et al., Nature 466 (2010) 470. [5] M. Schwab et al., J. Am. Chem. Soc. 134 (2012) 18169. [6] A. Narita et al., submitted. [7] C. Casitglioni et al., J. Chem. Phys. 114 (2001) 963. [8] R. Gillen et al., Phys. Rev. B 81 (2010) 205426.


Graphene on Hexagonal Substrates: Moiré Patterns and Electronic Properties J. R. Wallbank1, M. Mucha-Kruczyński1,2, A. A. Patel1,3, and V. I. Fal'ko1 Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK 2 Department of Physics, University of Bath, Bath, BA2 7AY, UK 3 Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India j.wallbank@lancaster.ac.uk 1

Abstract The electronic properties of graphene-based devices can be dramatically improved by placing graphene on an atomically flat hexagonal crystal surface. At the same time, a small lattice mismatch or misalignment angle results in the formation of the large, quasi-periodic structure known as a moiré pattern. This pattern is interesting for geometrical reasons, it acts like a magnifying glass, increasing the visibility of various types of defects. Moreover, it's effect on the graphene electrons can be described in terms of scattering using the simplest harmonics of the moiré pattern, which, when combined with the symmetry of the system, allows the Hamiltonian to be written in terms of a small number of phenomenological, substrate dependent, parameters. When the substrate in question has the lattice constant similar to graphene, such as hexagonal boron nitride, it is the intravalley scattering terms that will dominate [1]. Additionally, there are many substrates, including certain transition metal dichalcogenides, with a unit cell area approximately three times larger than that of graphene. In this case, the intervalley scattering terms will dominate. We investigate the characteristic features that appear in the graphene miniband spectrum, systematically exploring the space of phenomenological substrate parameters, and show that the zeroenergy Dirac spectrum always remains intact. For a large parametric regime of the intravalley substrate scattering, we find additional mini Dirac points (mDPs), isolated on the energy axis, between the top of the first moiré miniband and the bottom of the second. This contrasts with the intervalley scattering, which can open a band gap between the two minibands. Experimental consequences of the moiré minibands, and in particular the isolated mDPs, can be seen upon the application of an intermediate magnetic field: Both the Landau level spectra around the mDP and the sign change behaviour of the Hall coefficient upon doping through the mDP, mimic that of the main Dirac point at the conduction-valence band edge. In stronger magnetic fields, the large size of the moiré supercell makes this an ideal system to observe the effects of the Hofstadter butterfly. When the magnetic flux per moiré supercell, Φ=Φ 0 p/q, is increased to a significant rational fraction of the flux quanta, Φ 0, each Landau level is split into q magnetic minibands resulting in an interesting fractal pattern of energy bands with experimentally observable consequences [2]. References [1] J. R. Wallbank, A. A. Patel, M. Mucha-Kruczyński, A.K. Geim, V. I. Fal'ko, arXiv:1211.4711 (2012) [2] L. A. Ponomarenko, R. V. Gorbachev, D. C. Elias, G. L. Yu, A. S. Mayorov, J. R. Wallbank, M. MuchaKruczynski, A. A. Patel, B. A. Piot, M. Potemski, I. V. Grigorieva, K. S. Novoselov, F. Guinea, V. I. Fal'ko, A. K. Geim, arXiv:1212.5012 (2012) Figures Fig1: Examples of the moiré miniband structure for graphene on a hexagonal substrate subject to intravalley scattering (a), or intervalley scattering (b).


Graphenide Solutions and Films 1

Yu Wang1, Alain Pénicaud1, Pascal Puech2 Centre de Recherche Paul Pascal, CNRS, Université Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France 2 CEMES-CNRS, UPR8011, 29 rue Jeanne Marvig, BP 94347, Toulouse, Cedex 4, France wang@crpp-bordeaux.cnrs.fr

Up to this time, there has been substantial progress in the production of graphene on a large scale through solution route, which can replace the mechanical exfoliation and epitaxial growth on silicon carbide method. It was reported by our group recently that a method consists in exfoliating graphene from graphite and dispersing the graphene in organic solvents without applying sonication or surfactant 1-4. Our research is devoted to study the solutions of negatively charged graphene (graphenide) which are prepared from graphite intercalation compounds (GICs). The GICs are synthesized by reduction of graphite with an alkali metal, typically with potassium. Three different potassium GICs were synthesized and studied by resonant Raman scattering, by varying the exciting wavelength from UV to infrared, with important consequences for the characterization of the graphenide solutions Furthermore, graphene solutions were deposited on substrates and characterized by Raman. Finally, thin graphene films were made from the solution and preliminary studies on these (solution route) transparent conducting films will be presented. References [1]. C. Vallés, C.Drummond, H. Saadaoui, C.A. Furtado, M.S. He, O.Roubeau, L.Ortolani, M. Monthioux, A.Pénicaud. J. Am. Chem. Soc., 47 (2008), 15802-15804. [2]. A. Catheline, C.Vallés, C. Drummond, L.Ortolani, V.Morandi, M.Marcaccio, M.Lurlo, F.Paolucci, A. Pénicaud. Chem. Commun., 47(2011), 5470-5472. [3]. A. Catheline, L.Ortolani, V.Morandi, M.Melle-Franco, C. Drummond, C.Zakri, A. Pénicaud. Soft Matter, 12 (2012), 7882-7887. [4]. A. Pénicaud, C.Drummond. Acc.Chem.Res., 46 (2013), 129-137 Figures

Fig. Graphene flake in THF and Graphene based transparent film


Graphenide Solutions and Films 1

Yu Wang1, Alain Pénicaud1, Pascal Puech2 Centre de Recherche Paul Pascal, CNRS, Université Bordeaux, 115 Avenue Schweitzer, 33600 Pessac, France 2 CEMES-CNRS, UPR8011, 29 rue Jeanne Marvig, BP 94347, Toulouse, Cedex 4, France wang@crpp-bordeaux.cnrs.fr

Up to this time, there has been substantial progress in the production of graphene on a large scale through solution route, which can replace the mechanical exfoliation and epitaxial growth on silicon carbide method. It was reported by our group recently that a method consists in exfoliating graphene from graphite and dispersing the graphene in organic solvents without applying sonication or surfactant 1-4. Our research is devoted to study the solutions of negatively charged graphene (graphenide) which are prepared from graphite intercalation compounds (GICs). The GICs are synthesized by reduction of graphite with an alkali metal, typically with potassium. Three different potassium GICs were synthesized and studied by resonant Raman scattering, by varying the exciting wavelength from UV to infrared, with important consequences for the characterization of the graphenide solutions Furthermore, graphene solutions were deposited on substrates and characterized by Raman. Finally, thin graphene films were made from the solution and preliminary studies on these (solution route) transparent conducting films will be presented. References [1]. C. Vallés, C.Drummond, H. Saadaoui, C.A. Furtado, M.S. He, O.Roubeau, L.Ortolani, M. Monthioux, A.Pénicaud. J. Am. Chem. Soc., 47 (2008), 15802-15804. [2]. A. Catheline, C.Vallés, C. Drummond, L.Ortolani, V.Morandi, M.Marcaccio, M.Lurlo, F.Paolucci, A. Pénicaud. Chem. Commun., 47(2011), 5470-5472. [3]. A. Catheline, L.Ortolani, V.Morandi, M.Melle-Franco, C. Drummond, C.Zakri, A. Pénicaud. Soft Matter, 12 (2012), 7882-7887. [4]. A. Pénicaud, C.Drummond. Acc.Chem.Res., 46 (2013), 129-137 Figures

Fig. Graphene flake in THF and Graphene based transparent film


Scalable process for automated production of graphene oxide Rune Wendelbo Abalonyx AS, Forskningsveien 1, 0314 Oslo, Norway rw@abalonyx.no Abstract Abalonyx has developed a scalable process for the efficient production of high purity nano-particulate graphene derivatives Graphene Oxide (GO) and Reduced Graphene Oxide (RGO), and we are now ready to build and operate a production plant. The Abalonyx Graphene Oxide (GO) process is a modification of the “Hummers method” [1], with subsequent thermal reduction, “flashing” to RGO. The products have been extensively characterized, comprising SEM, XRD, IR, Raman, XPS, AFM, TEM, TGA, BET and DLS. AFM analysis indicates that the GO is single layer, whereas Raman results indicate an average of 2-3 layer particles.

Figure 1. Schematic process overview, including waste streams.

An extensive range of graphites were screened until we found a graphite raw-material that gives superior quality over the other graphites. The production process has been optimized so that it is safe, reproducible and fully scalable. The problems related to heat balance have been solved and we have designed a reactor that can produce up to 4 Kg of GO in one batch. The process has been partly automated, with plans for complete automation. The GO process has been run daily for 1 month with 100 g batches of graphite, producing 500 g batches of GO-paste with about 30 wt% GO [2]. It is well known that the Hummers method is difficult to control reproducibly. We have identified and addressed the following parameters as being critical. 1. Raw material. Out of a large number of graphites tested, we have identified one product - that gives high quality graphene oxide. 2. Reactor design. A cost efficient reactor that is perfectly scalable has been designed 3. Addition of reagents. The procedure for addition of the reagents has been optimized 4. Reaction temperature profile has been optimized. 5. Reaction time. The time for each reaction step has been optimized 6. Safety. Safety features have been designed to avoid runaway reaction 7. Automation. The most labor-intensive steps have been automated 8. Storing. Safe storage without product deterioration 9. Know-how. We possess extensive know-how related to the process


The production cost estimate (Figure 2) for a fully automated process has been worked out based on experience from our pilot reactor, reagent market prices, labor need and the following assumptions: 1. Reagent costs: 30 Euro per Kg at small volumes, decreasing to 20 Euros per Kg at max volumes. 2. Personnel: One person full time up to 4 Kg/day, then one extra person for each 10 X increment. 3. Personnel cost: 200 Euro per day per person 4. Infrastructure: From 200 Euro per day increasing by a factor 2 for each 10 X volume increase. 5. Waste management: 100 liters of acid waste per Kg product. Estimated cost 0.6 Euro/liter 6. Production plant cost: 200kE for 0.4 Kg/day capacity. Then 3 X more for each 10 X increment 7. Depreciation: Full write off/pay down over 4 years = 1000 working days.

Figure 2.Estimated production cost for GO as a function of volume per day. Red line: Net cost. Green line: Net cost including cost for waste management. Blue line: Net cost including cost for waste management and cost of 4 year depreciation

From the above Figure, it can be seen that â&#x20AC;&#x201C; under the present assumptions â&#x20AC;&#x201C; waste management represents 75 % of total costs at high production levels, where as the contribution from depreciation is only about 5 %. Thus, if the acid waste can be neutralized and deposited at the site, a production cost of about 22 Euros/Kg for graphene oxide is achievable.

Potential end uses of our material include batteries [3] and ultracapacitors, paints, composites and printed electronics. We are presently building network to parties along the different value chains. References [1] Hummers, W.S., and Offeman, R.E., J. Am. Chem. Soc., 80 (1958),1339â&#x20AC;&#x201C;1339. [2] Wendelbo, R. and Fotedar, S. Norw. Patent application No. 20120917. [3] Wendelbo, R. and Fotedar, S. Norw. Patent application No. 20121111.


Production of 3D‐shaped graphene via transfer printing Sinéad Winters1,2, Toby Hallam1 and Georg S. Duesberg.1,2 1

Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Ireland 2

School of Chemistry, Trinity College Dublin, Ireland

swinters@tcd.ie Abstract Graphene has attracted much research interest due to its exceptional mechanical and electronic properties. Graphene is generally considered to be completely flat; however, wrinkles and folds do naturally form in the material. Bends in graphene have been shown to alter its electronic and chemical properties, yet the controlled production of folds and wrinkles in graphene remains relatively unexplored. Intentional formation of folds in chemical vapour deposited graphene by pre-patterning of 1 the copper growth substrate has been previously reported, along with formation of ripples by thermal 2 annealing in suspended graphene and ripple formation due to buckling in graphene ribbons when 3 placed on a strained elastomeric substrate that is subsequently released. We have developed a novel method to produce three-dimensional folded graphene structures from 4 chemical vapour deposited graphene using a patterned elastomeric stamp and a polymer scaffold. The structures have been characterised using atomic force and scanning electron microscopy, Raman spectroscopy and cyclic voltammetry. Raman spectroscopy reveals doping of the graphene from the polymer substrate, while cyclic voltammetry indicates an increased surface area due to the folding of graphene. This production method provides an alternative means of creating intentional bends in graphene in a controlled manner.

1.

K. Kim, Z. Lee, B. Malone, K. Chan, B. Alemán, W. Regan, W. Gannett, M. Crommie, M. Cohen, and A. Zettl, Physical Review B, 83 (2011), 245433.

2.

W. Bao, F. Miao, Z. Chen, H. Zhang, W. Jang, C. Dames, and C. N. Lau, Nature Nanotechnology, 4 (2009), 562–6.

3.

Y. Wang, R. Yang, Z. Shi, L. Zhang, D. Shi, E. Wang, and G. Zhang, ACS Nano, 5 (2011), 3645–50.

4.

S. Winters, T. Hallam, H. Nolan, and G. S. Duesberg, Physica Status Solidi (B), 249 (2012), 2515–18.


Figures

Figure 1 Transfer and printing of graphene. (a) The PMMA/graphene film is lowered onto the PDMS stamp and the PMMA is dissolved. Upon drying, graphene conforms to the shape of the stamp. (b) PMMA is spuncast over the graphene and the PMMA graphene is stamped onto a SiO2/Si substrate.


Graphene Photoresponse for Mid-Infrared Light 1

1

1

1

1

Achim Woessner , Michela Badioli , Klaas-Jan Tielrooij , Gabriele Navickaite , Sébastien Nanot , 2 1 F. Javier García de Abajo and Frank H.L. Koppens 1

ICFO - Institute of Photonic Sciences, Av. Carl Friedrich Gauss 3, 08860 Castelldefels, Spain 2 IQFR-CSIC, Serrano 119, 28006 Madrid, Spain E-Mail: frank.koppens@icfo.es, achim.woessner@icfo.es

Abstract In addition to its well-known electronic properties and the absence of a band gap, graphene shows optical properties which are tunable by varying the concentration of the charge carriers by using for example electrostatic doping. It is an ideal opto-electronic material for a broad frequency range from ultraviolet to THz [1]. Graphene photocurrent in the visible, near-infrared and THz frequency ranges has been widely studied [2,3,4], but a detailed study of the photoresponse mechanism for mid-infrared frequencies has to our knowledge not been reported so far. We study graphene in the mid-infrared frequency range to elucidate the mechanism of photocurrent generation. We observe a photocurrent over a broad spectral range from 6 to 10 µm of wavelength. This photocurrent is tunable by applying a backgate voltage to vary the Fermi energy and therefore the number of charge carriers in the graphene. Using this tunability it is possible to switch the photocurrent on and off by Pauli blocking. This work paves the way towards different applications, such as electro-optic switches and room temperature infrared photodetectors.

References [1] F. Bonaccorso et al., Nature Photonics, 9 (2010) 611-622 [2] F. Xia et al., Nano Letters, 3 (2009) 1039-1044 [3] N.M. Gabor et al., Science, 6056 (2011) 648-652 [4] L. Vicarelli et al., Nature Materials, 11 (2012) 865-871


Influence of graphene concentration in TiO2-graphene nanocomposites on photocatalytic activity under UV light irradiation Malgorzata Wojtoniszak, Magdalena Onyszko, Ewa Mijowska West Pomeranian University of Technology in Szczecin, Institute of Chemical and Environment Engineering, Pulaskeigo 10, 70-322 Szczecin, Poland mwojtoniszak@zut.edu.pl Abstract Graphene has attracted much attention since its discovery in 2004. Because of its exceptional mechanical, electrical, thermal and optical properties, high surface area-to-volume ratio and unique atomic structure, graphene is expected to be applicable in many fields, including electronic devices (sensors, batteries), composites and nanomedicine among others [1-8]. Recently, graphene has been found as an amazing nanocarrier of other particles, for instance titanium dioxide. Hybridization of TiO2 with graphene affects on improvement of its photocatalytic activity. Electronic interaction between these two nanomaterials influences on transferring of excited electrons from the conduction band of TiO2 to the surface of graphene, thus improving the separation of the electron–hole pairs and preventing their recombination [9-11]. Furthermore, conjugation graphene with TiO2 influences on its band gap energy decrease, thus shifting the absorption threshold to the visible light region and allowing utilization of solar energy [11]. In this study, preparation, characterization and photocatalytic activity of TiO2-graphene nanocomposites will be presented. Nanocomposites were prepared using sol-gel method, followed by calcination at 400 °C, under vacuum or in air atmos phere, to create anatase phase of titanium dioxide adsorbed on graphene surface. In a typical procedure, 5%,7%,10% or 15% of titanium butoxide ethanol solution was mixed with graphene oxide ethanol dispersion in the volume ratio of 1:4, followed by sonication and magnetic stirring for 24 h. Next, the materials were centrifuged for 60 min., washed with ethanol in order to remove excess of titanium dioxide and finally calcinated for 2 h at 400 °C, under vacuum or in air atmosphere. The obtained nanocomposites were denoted as: T-G-5-V, T-G-5-A, T-G7-V, T-G-7-A, T-G-10-V, T-G-10-A, T-G-15-V and T-G-15-A. Additionally, for comparison purpose, TiO2 photocatalysts without graphene were prepared under the same conditions. The materials were characterized with transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and diffuse reflectance UV-vis spectroscopy. Photocatalytic activity of the prepared nanomaterials dependent on graphene concentration and calcination conditions was investigated. The photocatalytic activity of the materials was studied in model reactions of phenol decomposition under UV light irradiation.

References [1] Y.V. Aristov, G. Urbanik, K. Kummer, D.V. Vyalikh, O.V. Molodtsova, A.B. Preobrajenski et al., Nano Lett. 10 (2010) 992. [2] H. Zhao, K. Min, N.R. Aluru, Nano let. 9 (2009) 3012. [3] Y. Zhang, T.T. Tang, C. Girit, Z. Hao, M.C. Martin, A. Zettl et al., Nature 459 (2009) 820. [4] N.V. Medhekar, A. Ramasubramaniam, R.S. Ruoff, V.B. Shenoy, Acs nano. 4 (2010) 2300. [5] S. Wang, M. Tambraparni, J. Qiu, J. Tipton, D. Dean, Macromolecules 42 (2009) 5251. [6] Y. Chang, Toxicol. Lett. 200 (2010) 201. [7] S. Stankovich, D.A. Dikin, G.H.B. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach et al., Nature 442 (2006) 282. [8] J.D. Fowler, M.J. Allen, V.C. Tung, Y. Yang, R.B. Kaner, B.H. Weiller, ACS Nano 3 (2009) 301. [9] X.Y. Zhang, H.P. Li, X.L. Cui Chin. J. Inorg. Chem. 25 (2009) 1903. [10] M. Wojtoniszak, B. Zielinska, R.J. Kalenczuk, E. Mijowska Materials Science-Poland 30 (2012) 32. [11] M. Wojtoniszak, B. Zielinska, X. Chen, R.J. Kalenczuk, E. Mijowska J Mater Sci 47 (2012) 3185.


Figures

Figure 1. Transmission electron microscopy image of TiO2-graphene nanocomposite denoted as T-G10-V.

Figure2. Photocatalytic activity of TiO2-graphene nanocomposites and pristine TiO2 photocatalysts measured as phenol degradation rate after 90 minutes irradation.


Ideal Strength of Doped Graphene Sungjong Woo, Young-Woo Son KIAS Hoegiro 87, Dongdaemun-gu, Seoul 130-722, Korea sjwoo@kias.re.kr A recent nanoindentation experiment, which has shown that graphene is the strongest two dimensional meterial, reports that the intrinsic strength of graphene is 42 N/m at the nominal equibiaxial breaking strain of 0.225 [1]. This was followed by a theoretical calculation [2] showing the quite smaller breaking strain of 0.15 than the measured value. It is unusual since materials under strain typically fail before they reach the ideal strength. We have considered electronic doping as a possible external factor to reduce the gap between the experiment and theory [3]. While the mechanical distortions change the electronic properties of graphene significantly, the effects of electronic manipulation on its mechanical properties have not been well known. Using first-principles calculation methods, we show that, when graphene expands isotropically under equibiaxial strain, both the electron and hole doping can improve its ideal strength and enhance the critical breaking strain dramatically. We have further found that, contrary to the isotropic expansions, under uniaxial strain, the electron doping decreases the ideal strength as well as critical strain of graphene while the hole doping increases both. Strengthening or weakening of graphene upon doping is associated with the modification of Fermi surfaces, electron-phonon interaction, Kohn anomaly and the change of electronic band structures. We will discuss the distinct failure mechanisms which depend on type of strains related with the different doping-induced mechanical stabilities and instabilities. References [1] C. Lee, X. Wei, J. W. Kysar, and J. Hone, Science, 321 (2008) 385. [2] C. A. Marianetti and H. G. Yevick, Physical Review Letters, 105 (2010) 245502. [3] arXiv:1211.0355, accepted for publication on Physical Review B (2013).


Dirac-Like Plasmons in Honeycomb Lattices of Metallic Nanoparticles C. Woollacott, Dr. E. Mariani University of Exeter, Stocker Road, Exeter, UK, EX4 4QL cw289@ex.ac.uk Abstract Light has inspired science and art for millennia. The interaction of light with metals resulted in remarkable technological as well as artistic breakthroughs, like the invention of mirrors and of stained glass windows. In fact the colour of the latter is generated from light interacting with small metallic particles embedded within the glass, and can be controlled by changing the shape, size and material of these particles. This interaction has been explored further, with the discovery that individual nanoparticles can be used to trap light to the nano-scale. Along this direction the rapid evolution of nano-physics allowed control over the production of arrays of metallic nanoparticles that can trap light and transport it over macroscopic distances [1]. In this theoretical project, inspired by the unique properties exhibited by graphene [2], we analytically explore two-dimensional honeycomb arrays of metallic nanoparticles (see figure 1). Each of these nanoparticles supports a localized surface plasmon. We study the quantum properties of the collective plasmons (CP), resulting from the near field dipolar interaction between the nanoparticles, which transport energy through the system. These CPs behave as peculiar relativistic quantum particles (massless Dirac bosons, see figure 2) whose behaviour can be tuned by the polarisation of light (see figures 3 and 4). We analytically investigate the dispersion, the effective Hamiltonian and the eigenstates of the CPs for an arbitrary orientation of the individual dipole moments. When the polarization points close to the normal to the plane the spectrum presents Dirac cones, similar to those present in the electronic band structure of graphene. We derive the effective Dirac Hamiltonian for the CPs and show that the corresponding spinor eigenstates represent Dirac-like massless bosonic excitations that present similar effects to electrons in graphene, such as a non-trivial Berry phase and the absence of backscattering off smooth inhomogeneities. We further discuss how one can manipulate the Dirac points in the Brillouin zone and open a gap in the CP dispersion by modifying the polarization of the localized surface plasmons, paving the way for a fully tunable plasmonic analogue of graphene. The remarkable fact that the plasmonic dispersion can be tuned could open new horizons in highdefinition microscopy and in ultrafast electronic devices that will benefit from the unimpeded propagation of information carried by the novel CP [3].

References [1] C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley-VCH, Weinheim, 2004) [2] K. S. Novoselov et al., Science 306 (2004) 666 [3] G.Weick, C. Woollacott, W. L. Barnes and E. Mariani, Phys. Rev. Lett. in press (2013) arXiv:1209.5005v2


Figures

Fig. 1: A honeycomb lattice of metallic nanoparticles, the same structure as carbon atoms in graphene.

Fig. 2: The CP dispersion for a honeycomb array of metallic nanoparticles, with polarisation normal to the plane, showing the emergence of pseudorelativistic physics.

Fig. 3: The CP dispersions for a honeycomb array of metallic nanoparticles for three different light polarisations.

Fig. 4: By changing the in-plane angle ( ) and out-of-plane angle ( ) of the orientation of the dipole moments of the localized surface plasmons on the metallic nanoparticles, the CP dispersion can either be gapless and graphene-like (blue) or have a gap (yellow).


Large-scale single layer graphene synthesized by optimized APCVD method Ke Xiao, Huaqiang Wu, Hongming Lv, Xiaoming Wu, He Qian Institute of Microelectronics, Tsinghua University, Beijing, 100084, China wuhq@mail.tsinghua.edu.cn; Abstract It is observed that the cooling conditions, including the cooling rate and cooling atmosphere, are the key parameters to control the coverage, thickness, and uniformity of graphene growth on Platinum by atmospheric pressure chemical vapor deposition (APCVD) method. As show in Table 1, a series of experiments were carried out with different cooling parameters to examine the cooling condition effects in detail for the first time. The objective of this study is to find out the optimized growth conditions for large-scale, single layer graphene growth. The surface morphology which reveals the coverage and uniformity of the grown graphene was observed by SEM directly on Pt substrate, and observed by optical microscope (OM) after transferring the graphene to SiO2(300nm)/Si substrates. As shown in Fig. 1, the fast cooling group gave the coverage of graphene almost 100% under different gas compositions. The deep colored sheets in the OM images indicate multi-layer graphene islands. As shown in Fig. 1b, c, e and f, the size of multi-layer graphene islands is reduced when H2 was introduced in the S2 and S3 samples. The smallest size and least amount of multi-layer graphene islands are observed in the mixture gas (CH4 and H2) environment. For slow cooling group, as shown in Fig. 2, the graphene coverage is much less and large separation of grown graphene sheets could be found. Only small pieces of graphene, as shown in Fig. 2b and e, could be observed in the case of H2 environment. Based on those experimental results, in general, the graphene coverage is higher with fast cooling conditions than slow cooling ones. Fast cooling with the mixture gas of H2 and CH4 environment offers preferred single-layer graphene growth. Four-step reactions are proposed to explain the graphene growth mechanism during cooling process:  1) release: carbon atoms segregate from Pt and bond to each other to form graphene structures[1], 2) etch: the bonded carbon atoms could react with H2 during cooling down to form C-H bond, and graphene is etched[2,3]; and 3) thermal decomposition: carbon atoms (from CH4 thermal decomposition) participate in forming graphene on Pt surface; and 4) diffuse: instead of release from Pt, the dissolved carbon atoms diffuse in the substrate[4]. As shown in Fig. 3, depending on the cooling conditions, only partial of those four-step reactions happened in the designed experiments from S1 to S6. In the fast cooling group, the diffusion reaction doesn’t occur because the carbon atoms couldn’t get enough time to diffuse into Pt before the system cools down to low temperature. The cooling atmosphere affects the reaction process significantly. In S1 experiments, only Argon gas is used during cooling down. The etching and thermal decomposition reactions don’t occur because of the absence of CH4 and H2. Only carbon atoms release step was happened. Single-layer graphene films are formed in the low carbon concentration region and multi-layer graphene islands are found in the high carbon atoms concentration region (as shown in Fig. 3). In S2 experiments, only hydrogen gas is used during cooling down. Both carbon atoms release and etch reaction steps occurred. Some weak-bonded carbon atoms structure could be more easily etched away by H2. Due to the etching effects, the graphene coverage is lower and the size of multi-layer graphene is smaller in comparison to Ar atmosphere case. In S3 experiments, both CH4 and H2 gases were used during cooling down. Three reactions occurred and the resulted graphene films are combined effects from carbon atoms release, etch and CH4 thermal decomposition. Since CH4 could provide additional carbon atoms and H2 could etch away weak bonded carbon atom structures, the graphene coverage is the highest with single layer graphene, as shown in Fig. 3. While in the slow cooling cases, carbon atoms could get enough time to diffuse in Pt and react with H2 before the temperature falls. This effect will reduce the carbon atoms participating in forming graphene, resulting in lower graphene coverage and uniformity on Pt surface. Particularly, for S5 experiment, the H2 etch effect is enhanced by the slow cooling rate, the etching process become dominant during cooling step and removes almost all graphene. Fast cooling in mixture gas of CH4 and H2 is the optimized choice for growing good quality and single-layer graphene with high coverage. As shown in Fig. 4 to Fig. 7, various characterization techniques (Raman, OM, SEM, TEM, AFM, etc.) were applied to examine the graphene morphology and quality. Back-gated field effect transistor was fabricated (OM image of the device is shown in Fig. 8) and the extracted carrier mobility is up to 1,600 cm2V-1s-1. Table 1. Cooling conditions for experiments S1 to S6 Index S1 S2 S3 S4 S5 S6

Cooling Rate Fast Fast Fast Slow Slow Slow

Cooling Atmosphere 800sccm Ar 800sccm H2 800sccm Mixture of CH4 and H2 ( CH4:H2=0.076:1) 800sccm Ar 800sccm H2 800sccm Mixture of CH4 and H2 ( CH4:H2=0.076:1)

References 1. M. Gao, Y. et.al, Appl. Phys. Lett. 2011, 98, 033101 2. I. Vlassiouk, et.al, ACS Nano, 2011, 5, 6069. 3. M. Losurdo, et.al, Phys. Chem. Chem. Phys. 2011, 13, 20836. 4. Q. Yu, et.al, Appl. Phys. Lett. 2008, 93, 113103.


Figures

Fig.1. SEM and OM images of the transferred graphene films grown on Pt substrates with fast cooling. (a), (d). 800sccm Ar, (b), (e).800sccm H2, and (c), (f). 800sccm mixture of CH4 and H2(0.076% CH4). Scale bars are 100μm.

Fig.4.(a) Raman spectra of single-layer graphene. Inset shows the optical image of single-layer graphene. The multi-layer island, wrinkle and residue PMMA caused by transfer are indicated by the black, blue and green arrows, respectively. The Raman sampling point is marked out by red circle. Scale bar is 100μm.

Fig.5. SEM image graphene grown on Pt. Scale bar is 10μm.

Fig.2. SEM and OM images of the transferred graphene films grown on Pt substrates with slow cooling. (a), (d). 800sccm Ar, (b), (e). 800sccm H2, and (c), (f). 800sccm mixture of CH4 and H2 (0.076% CH4). Scale bars are100μm.

Fig. 6. AFM image of graphene transferred onto Si substrate with 300μm SiO2. Scale bar is 1μm.

Fig.7. HRTEM image show excellent crystallinity of graphene film. Inset shows the electron diffraction pattern of the graphene film.

Fig.3. The reactions during cooling effect and the resulted carbon atoms distribution on Pt substrate after cooling in experiments S1 to S6.

Fig.8. OM image graphene FET.

of

back-gated


Three-dimensional Nitrogen and Boron Co-doped Graphenes for High-Performance All SolidState Supercapacitors Zhong-Shuai Wu, Xinliang Feng, and Klaus M端llen Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany wuzs@mpip-mainz.mpg.de Abstract Three-dimensional (3D) graphene-based frameworks, such as aerogels, foams, and sponges are an important class of new-generation porous carbon materials, which exhibit continuously interconnected macroporous structures, low mass density, large surface area and high electrical conductivity. These materials can serve as robust matrix for accommodating metal, metal oxide and electrochemically active polymers for various applications in ECs, batteries, and catalysis.1-3 Herein we demonstrate a simplified prototype device of high-performance ASSSs based on 3D nitrogen and boron co-doped monolithic graphene aerogels (BN-GAs, Figure 1). The device possesses an electrode-separator-electrolyte integrated structure, in which the GAs serve as additive/binder-free electrodes and a polyvinyl alcohol (PVA)/H2SO4 gel as solid-state electrolyte and thinner separator. The nitrogen and/or boron doping in carbon networks can facilitate charge transfer between neighboring carbon atoms and thus enhance the electrochemical performance of carbon-based materials. The as-prepared GAs show 3D interconnected frameworks with a macroporous architecture, which are favorable for ion diffusion and electron transport in bulk electrode. Further, monolithic BN-GAs can be easily processed into thin electrode plates with a desirable size upon physical pressing. As a consequence, the resulting BN-GAs based ASSSs exhibit not only minimized device thickness, but also show high specific capacitance (~ 62 F g-1), good rate capability, and enhanced energy density (~8.65 Wh kg-1) or power density (~1600 W kg-1) with respect to undoped (U-GAs), nitrogen doped (N-GAs), boron doped (B-GAs) GAs, or layer-structured graphene paper (GP) (Figure 2). Aerogels built of wellinterconnected ultrathin graphene sheets can provide high surface area, 3D macroporosity and high electrical conductivity, which are favorable for enhancing solid-state ion and electron transport in supercapacitors. References [1] Wu, Z. S.; Winter, A.; Chen, L.; Sun, Y.; Turchanin, A.; Feng, X.; M端llen, K. Adv. Mater., 24(2012)5130. [2] Wu, Z. S.; Sun, Y.; Tan, Y. Z.; Yang, S. B.; Feng, X. L.; M端llen, K. J. Am. Chem. Soc., 134(2012) 19532. [3] Wu, Z. S.; Yang, S. B.; Sun, Y.; Parvez, K.; Feng, X. L.; M端llen, K. J. Am. Chem. Soc., 134(2012) 9082. Figures

Figure 1. Fabrication illustration of ASSSs based on BN-GAs that were involved by a combined hydrothermal process and freeze-drying process. The as-fabricated supercapacitors with a diameter of 7 mm indicated by green dot ring and its simplified schematic of ASSSs based on aerogels (left down).


Figure 2. a) CVs of BN-GAs based ASSSs measured at the scan rates of 5, 20 and 50 mV s-1. b) Ragone plot of ASSSs based on U-GAs, N-GAs, B-GAs, BN-GAs and GP, based on two-electrode mass of active materials.


Graphene-Enhanced Raman Scattering of Biomolecules Fatemeh Yaghobian, Tobias Korn and Christian Sch端ller Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany Fatemeh.Yaghobian@physik.uni-regensburg.de

Abstract Highest sensitivity in detecting and identifying chemical compounds is achieved by surface-enhanced Raman scattering (SERS), which occurs from molecules adsorbed on nanostructured metallic surfaces or metal nanoparticles. In general, Raman scattering is too weak to produce signals from monolayer samples and Raman signal enhancement requires coupling of the analyte to the SERS-active surface [1,2]

. Due to the need for great repeatability, lowest uncertainty and highly tunable surface morphologies,

highly reproducible graphene surfaces are shown to be potential candidates for obtaining comparable results. Graphene has been of significant interest recently with respect to graphene-enhanced Raman scattering (GERS), that results in enhancement of the native Raman signal of target molecules in close proximity to mono- and multilayers of graphene by several orders of magnitude. Since there are increasing needs for methods to conduct reproducible and sensitive Raman measurements, GERS is emerging as an important method. Graphene sustains particularly large enhanced Raman signals of molecules at its surface

[3-5]

.

In this work, we study the enhancement of the Raman signal of biomolecules on graphene and evaluate the enhancement factors and reproducibility. Graphene mono- and multilayers, prepared on suitable surfaces, shall be qualified as biocompatible and highly reproducible SERS-active substrates. Even though the mechanisms are not clear, it is of metrological importance to compare the GERS enhancement with SERS measurements. We have first chosen 4-mercapto-benzoic acid (4-MBA) to study the effect of graphene as an active substrate for signal enhancement and also the charge transfer of molecules adsorbed on it. This compound was chosen because of the strong affinity of the mercapto (-SH) end group to noble-metal and semi-metal surfaces, which leads to the spontaneous formation of a self-assembled monolayer (SAM). In Fig. 1 (left), we compare native Raman spectra of 4-MBA on silicon dioxide (SiO2) and graphite substrates along with graphene-enhanced signals of the molecule. The lowest (red) spectrum in Fig. 1 was taken on the SAM on the SiO2 substrate. If we compare this spectrum to the spectrum, measured on graphite (blue spectrum in Fig. 1) and on graphene (black -1

spectrum in Fig. 1), we observe that, interestingly, the former peak shifts to 1100 cm , when 4-MBA in the form of a single monolayer is attached to the surface of graphite or graphene instead of SiO 2. As can be seen in Fig. 1, also the strongest enhancement appears for the mode at 1100 cm

-1 [5]

.


Figure 1. (left) Raman spectrum of 4-MBA measured on SiO2 (red) and graphite (blue) along with the obtained enhanced Raman signal on graphene (black). (right) Raman spectrum of 4-MBA measured on SiO2 (red) along with the obtained enhanced Raman signal on silver nanoparticles (black). The inset shows an SEM image of silver nanoparticles [5].

The SERS measurements were also done on active substrates covered with spherical silver nanoparticles. The spectra in Fig. 1 (right) show that, in contrast to the measurements on graphene, no -1

shift of the CC breathing mode at 1074 cm is observed on a surface covered with silver nanoparticles and the SERS signal appears on the same position as in the native spectrum on SiO2. The enhancement factor in SERS is larger than what is achieved in GERS. However the main barrier to the routine use of SERS in analytical chemistry is the lack of robust methods to perform reliable quantitative analysis and the main reason for this is the lack of reproducible substrates, capable of high Raman enhancement. So the fact that graphene is easily reproducible and highly quantifiable makes it an excellent substrate for enhanced Raman probing

[5]

.

We have also found that mono- and multilayer graphene works as an active substrate for the observation of enhanced Raman scattering from adenine and cytosine in their physiological concentration ranges.

References [1] F. Yaghobian, T. Weimann, B. G端ttler, R. Stosch, Lab Chip, 11 (2011) 2955. [2] R. Stosch, F. Yaghobian, T. Weimann, R. J. C. Brown, M. J. T. Milton, B. G端ttler, Nanotechnology, 22 (2011) 105303. [3] X. Ling, L. Xie, Y. Fang, H. Xu, H. Zhang, J. Kong, M. S. Dresselhaus, J. Zhang and Z. Liu, Nano Lett. 10 (2010) 553. [4] Q. Hao, S. M. Morton, B. Wang, Y. Zhao, L. Jensen, and T. J. Huang, Appl. Phys. Lett. 102 (2013) 011102. [5] F. Yaghobian, T. Korn, and C. Sch端ller, ChemPhysChem, 13 (2012) 4271.


Study of thickness uniformity and wrinkling in epitaxial graphene grown on SiC polytypes 1

1

2

2

3

G. Reza Yazdi, T. Iakimov, M. Neek-Amal, F. M. Peeters, A. Zakharov, R. Yakimova 1

1

Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden

2

Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium 3

MaxLab, Lund University, S-22100 Lund, Sweden yazdi@ifm.liu.se

Abstract Growth of epitaxial graphene was performed on the Si face of SiC substrates in an inductively heated furnace at a temperature of 2000°C and at an ambient argon pressure of 1 atm. We have studied thickness uniformity and wrinkling on graphene grown on 4H-SiC(0001), 6H-SiC(0001), and 3C-SiC(111) substrates. Graphene surface morphology, thickness, band structure, structure and electronic properties have been assessed by using AFM, LEEM, ARPS, STM, and STS respectively. Graphene formation has been analyzed in respect to step bunching and surface decomposition energy differences created by the SiC basal plane stacking sequence on different SiC polytypes. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. The uniformity of silicon sublimation is an important factor for obtaining large area homogenous graphene. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have demonstrated a monolayer (ML) graphene growth on all SiC polytypes, but larger area, over 50 50

2

m , on cubic SiC (Fig. 1a). To study the surface restructuring

during SiC sublimation we examined around 300 steps for each sample using AFM. The corresponding histogram of the step height for 4H-SiC (Fig. 1b) indicates that two bilayer-height steps are the most probable and four bilayer-height steps show a significant probability. For the 6H-SiC sample (Fig. 1c) two and three bilayer-height steps dominate. On the 3C-SiC graphene sample one Si-C bilayer height has the highest percentage (48%) of appearance although some larger steps are present (Fig. 1d). The sublimation rate of 3C-SiC is the same over the whole defect-free substrate surface due to the similar decomposition energy on all step terraces, this providing a uniform source of C on the surface which results in a superior uniformity of the grown graphene layer. It is worth noting that C contained in one unit cell (three Si-C bilayers) of 3C-SiC is sufficient to feed the formation of 1ML graphene. The 6H-SiC polytype shows close quality of graphene to that on the 3C-SiC polytype, because half of the unit cell contains three Si-C bilayers. The results for the 4H-SiC substrate coverage by graphene show that graphene formation process has narrower window of growth parameters. We have found that single Si-C bilayer steps with the same decomposition energy in the beginning of the graphene formation are the controlling factors for the uniformity of Si subtraction. Having a rather low step height distribution is one advantage of our results, since it has been reported that the resistance of epitaxial graphene on SiC increases linearly with step height on the substrate [1]. Wrinkling is a very general phenomenon in nature with dimensions spanning across length scales from meters down to nanometers. Graphene wrinkles (Fig. 2a) easily and often. They are larger in dimension and form by compressive strain induced during cooling from the growth temperature due to the


difference in thermal expansion coefficients of graphene and SiC. Wrinkles are linear defects which can cause carrier scattering and decrease mobility. [2] Deep understanding and sufficient control of the wrinkle appearance are central to our current research interest. By modifying substrate conditions we have been able to change the wrinkle orientation from a random network to a full alignment (Fig. 2b) in a particular direction or radial, by partially reducing strain. By these results we have found out how the step size and point defect can rule wrinkle morphology. The behaviour of wrinkles during thermal cycling at the same temperature and different temperatures and also cooling down to 4 K has been studied. We also examine to what extent the electronic and structural integrity of graphene is preserved upon wrinkle formation by STM and STS. We will also present, from typical AFM images, an approximate evaluation of strain for the top graphene layer forming wrinkle network on different SiC samples with diverse wrinkle morphology and size. We observed that the wrinkles appear very rare in SiC wafers in comparison with small size of SiC substrates. It seems that the larger size of graphene sheets can sustain more compressive strain and avoid wrinkling. Wrinkling was studied in a series of computer simulation. The simulations were performed with the molecular dynamic method using AIREBO forcefield which is quite suitable for simulation of hydrocarbons and the Tersoff potential for Si-C simulation. The simulated samples have about 150,000 atoms including both graphene and substrates. The results confirmed the experimental findings of wrinkle formation. References [1] T. Low, V. Perebeinos, J. Tersoff, Ph. Avouris, Phys. Rev. Lett, 108 (2012) 096601. [2] S.V. Morozov, K.S. Novoselov, M.I. Katsnelson, F. Schedin, L.A. Ponomarenko, D. Jiang, and A.K. Geim, Phys.Rev. Lett., 97 (2006) 016801. Figures

Fig. 1- a) LEEM image of graphene on 3C-SiC, Histograms of step heights for a) 4H, b) 6H, and c) 3C-SiC

(a)

(b)


Fig. 2- a) STM image of part of a wrinkle b) Sketch of step size effect on wrinkles orientation


Preparation of graphene using solvent dispersion method and its functionalization a,b

Wesley R. Browne,

Xiaoyan Zhang,

a,b

a

Bart J. van Wees and Ben L. Feringa

a,b

a

Zernike Institute for Advanced Materials, University of Groningen, The Netherlands

b

Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. xiaoyan.zhang@rug.nl

Abstract Graphene, a one atom thick layer of carbon atoms with a two-dimensional honeycomb lattice, has drawn a lot of attention during the last past few years due to its unique properties.

1

Graphene holds the promise in a range of applications from electronic devices, composites to 2

biological applications. However, a prerequisite is to obtain high quality graphene in a large 1

3

scale. Several approaches have been developed, including mechanical, epitaxial, reduction 2

of graphene oxide, or solvent dispersion of graphite.

4

Among these methods, solvent

dispersion of graphite seems to be the simplest approach to prepare dispersible and defect-free graphene sheets. However, the graphene sheets in these solvents tend to precipitate due to strong Ď&#x20AC;-Ď&#x20AC; interactions. Chemical functionalization of graphene through non-covalent or covalent approaches is expected to improve the stability and processability of dispersed graphene, and may also introduce new properties, which is useful in tuning the properties of graphene for various applications. 4

In this presentation, the preparation of solvent dispersed graphene will be discussed together 5,6

with approaches to covalent, 7,8

organometallic precursor,

or non-covalent functionalization with

porphyrin,

5

etc. using cycloaddition or beam deposition methods.

References: [1] A. K. Geim, K. S. Novoselov, Nature Mater., 6 (2007), 183. [2] Y. W. Zhu, S. Murali, W. W. Cai, X. S. Li, J. W. Suk, J. R. Potts, R. S. Ruoff, Adv. Mater., 22 (2010), 3906. [3] W. Strupinski, K. Grodecki, A. Wysmolek, R. Stepniewski, T. Szkopek, P. E. Gaskell, A. Gruneis, D. Haberer, R. Bozek, J. Krupka, and J. M. Baranowski, Nano Lett., 11 (2011), 1786. [4] X. Y. Zhang, A. C. Coleman, N. Katsonis, W. R. Browne, B. J. van Wees, B. L. Feringa, Chem. Commun., 46 (2010), 7539. [5] X. Y. Zhang, L. L. Hou, A. Cnossen, A. C. Coleman, O. Ivashenko, P. Rudolf, B. J. van Wees, W. R. Browne, B. L. Feringa, Chemistry-A European Journal, 17 (2011), 8957. [6] X. Y. Zhang, W. R. Browne, B. L. Feringa, RSC Advances, 2 (2012), 12173. [7] W. F. van Dorp, X. Y. Zhang, B. L. Feringa, J. B. Wagner, T. W. Hansen, J. Th. M. De Hosson, Nanotechnology, 22 (2011), 505303. [8] W. F. van Dorp, X. Y. Zhang, B. L. Feringa, J. B. Wagner, T. W. Hansen, J. Th. M. De Hosson, ACS Nano, 6 (2012), 10076.


Contribution (Poster)

Chemically Derived Graphene for the Detection of NO2 1

1

1

2

Alexander Zöpfl , Wendy Patterson , Thomas Hirsch , Günther Ruhl , 1 1 Otto S. Wolfbeis , Frank-M. Matysik 1

Institute of Analytical Chemistry, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany 2 Infineon Technologies AG, 93049 Regensburg, Germany alexander.zoepfl@chemie.uni-regensburg.de

Since its discovery, graphene was suggested as very sensitive in binding molecules, enabling even the detection of a single molecule [1]. Chemically derived graphene is an interesting candidate for many types of sensors, and in particular for gas sensors. Sensor-based detection of gases is an important task to improve safety and quality of life. Highly sensitive metal oxide based gas sensors are well established and widely implemented [2]. However, they operate at high temperatures (250 - 600°C), which requires excessive energy and degrades their long term stability. In this respect, graphene-based gas sensors may be an inexpensive alternative. Upon gas adsorption, the conductance changes rapidly and with high sensitivity, even when operated at low temperatures (25 - 85 °C). In this study, graphene was prepared by reduction of graphene oxide (GO), which was obtained by oxidation of graphite (Hummers method) [3,4]. The resulting reduced graphene oxide (rGO) can be dispersed in water, enabling easy transfer to any substrate. Spin coating was determined to be the most effective transfer method, resulting in consistent layers with reproducible quality. To test the capability of rGO as a gas sensor material, the conductivity of rGO modified electrodes was studied in the presence of various gases at ambient conditions. The change in resistivity of rGO coated electrodes upon adsorption of NO2 allowed a minimum detection of 0.3 ppm (S/N = 3). As synthesized, this material is also sensitive to the detection of other gases, such as CH 4 and H2. To introduce selectivity, chemical modifications of rGO were implemented by attaching of functional groups and by doping with metals and metal oxides. Functionalization was performed by wet chemical and electrochemical methods. The reversibility and concentration dependence of the sensor was evaluated by continuous adsorption and desorption of NO2. Many important parameters affecting the sensor properties were investigated. Of these, humidity had the greatest influence on the electrical conductivity changes and reversibility. Therefore, a constant operation temperature of 85°C was used for all measurements (Fig. 1). Here, it has been shown that rGO is a suitable material for gas sensors due to its high sensitivity, inexpensive synthesis, ease of transfer to a substrate, and selectivity upon functionalization. With proper arrangement of various modified rGO electrodes onto an array, an artificial nose for gas detection could be realized.

The research was supported by Deutsche Forschungsgesellschaft (GRK 1570).


Contribution (Poster)

References [1]

F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson, K. S.Novoselov, Nature Mater. 6(9), 652–655 (2007)

[2]

A. Tricoli, M. Righettoni, A. Teleki, Angew. Chem. Int. Ed. 49(42), 7632–7659 (2010)

[3]

W. S. Hummers, R. E. Offeman: Preparation of Graphitic Oxide, J. Am. Chem. Soc. 80, 1339 (1958)

[4]

D. Li, M. B. Müller, S. Gilje, R.B. Kaner, G. G. Wallace, Nature Nanotech. 3, 101 (2008)

Figures

Figure 1:

Normalized change in electrical resistivity of microelectrodes coated with rGO in the presence of (a) 100 ppm NO2 at different temperatures and (b) different concentrations of NO2 with varying humidity.


Spin Transport in High Mobility Graphene Devices P. J. Zomer, M. H. D. Guimarães, A. Veligura, T. Maassen, I. J. Vera-Marun, N. Tombros, and B. J. van Wees Zernike Institute for Advanced Materials, Nijenborgh 4, Groningen, The Netherlands p.j.zomer@rug.nl Graphene is an excellent material for carrying spin information over long distances. At room temperature, a single layer graphene flake based on a SiO2 substrate typically shows a spin relaxation time τ of ~150 ps and spin relaxation length λ of ~2 µm [1]. This clearly shows the potential that graphene possesses for spin transport. However, the measured spin relaxation time and length are still orders of magnitude smaller than what is theoretically predicted and the exact cause for this discrepancy remains unclear. In order to pinpoint the limiting factors for graphene spin transport we follow two approaches to obtain superior quality devices as compared to the standard SiO2 based samples. First, the graphene flakes 5 2 are suspended, yielding charge carrier mobilities µ up to 3 x 10 cm /(V s) [2]. Second, the SiO2 is 4 2 replaced by hexagonal boron nitride (BN), where µ reaches 4 x 10 cm /(V s) [3]. Surprisingly, τ appears to remain unaffected, although for suspended graphene devices we find that the measured τ represents only a lower bound. For both cases we obtain a moderate increase in the maximum spin relaxation length λ ≥ 4.5 µm, which is caused by an enhancement of charge carrier diffusion in the high mobility devices. For BN-based devices we could measure spin transport over record lengths up to 20 µm. From further analysis of our data, we find it best described by a combination of a D’Yakonov-Perel and ElliottYafet like spin relaxation mechanism. Our measurements indicate that graphene roughness, charged impurities our surface phonons are not the dominant factor for spin relaxation in graphene. The improved device quality allows for spin transport over longer distances, but the experimental results can only give a lower bound for τ and λ. To shed more light on the matter, other aspects such as adsorbates on the graphene surface should be investigated. References [1] N. Tombros, C. Jozsa, M. Popinciuc, H. T. Jonkman, and B. J. van Wees, Nature 448 (2007) 571. [2] M. H. D. Guimarães, A. Veligura, P. J. Zomer, T. Maassen, I. J. Vera-Marun, N. Tombros, and B. J. van Wees, Nanoletters 12 (2012) 3512. [3] P. J. Zomer, M. H. D. Guimarães, N. Tombros, and B. J. van Wees, PRB 86 (2012) 161416(R). Figures

Scanning electron microscope images of a suspended (left) and a BN based spintronic graphene device (right) with cobalt electrodes. Part of the latter device is based on SiO2 for comparison.


(Two page abstract format: including figures and references. Please follow the model below.) Stability and kinetics of the butterfly defect in bilayer graphene from first principles Jon Zubeltzu, Fabiano Corsetti, Andrey Chuvilin and Emilio Artacho Nanogune, Tolosa Hiribidea, 76, Donostia, Spain j.zubeltzu@nanogune.eu Abstract (Arial 10) Graphene is a very promising material for a large variety of applications due to its singular properties. These properties can be modified by defect formation in the sample; therefore, the study of these 1 formations could help to control the properties of graphene . Andrey Chuvilin has observed by TEM that in bilayer graphene under electron radiation one type of divacancy defect is formed for lower electronic energies than the displacement threshold energy for monolayer graphene (personal communication). This defect, known as the butterfly defect, is shown in figure 1 and figure.

Figure 1. Experimental TEM image where the butterfly defect can be clearly observed. (Image obtained by Andrey Chuvilin, unpublished).

Figure 2. Relaxed DFT simulation of the butterfly defect. Four pentagons (green), four heptagons (red) and one central hexagon (blue) are created. The central hexagon is 30ยบ rotated compared to the original configuration

In order to observe the influence that the addition of the second layer has on the creation and stabilization of the butterfly defect, we have studied the change in stability of the defect between monolayer and bilayer graphene and the kinetic process of its creation. We have used the SIESTA 2 method , based on first principles DFT calculations to carry out the calculations. In order to analyze the stability of the butterfly defect in monolayer and bilayer graphene we have calculated its formation energy. The obtained values are shown in table 1. The difference between the formation energies is very small (0.14 eV) compared with the maximum kinetic energy that an atom can obtain (15-20 eV) for typical experimental 3 energies of the incoming electrons (80-100 keV) .

Type system

of

Formation energy (eV)

Monolayer

7.079

Bilayer

6.939

Table 1. As the stability of the defect does not explain the experimentally-observed effect, it appears possible that the second layer catalyzes the creation of the butterfly defect, or at least, that of the vacancy. In order to verify this hypothesis, we have simulated the electron-atom collision by giving an initial velocity to one atom. Then, we let the system evolve in time by ab initio molecular dynamics (AIMD). In order to know if any atom is expulsed due to the collision with the electron, we determine the emission threshold energy, which, by definition, is the minimum kinetic energy, required to expulse an atom from the system. We observe that the atoms need at least the same amount of energy to be removed in the bilayer system as in the monolayer one. We conclude that no atom can be expulsed to create the butterfly defect. Instead, we consider the formation of a Frenkel defect that could be energetically more favorable: in this case, an atom is expulsed from one layer to create a vacancy,


remaining trapped between the two layers and thereby creating an interstitial defect. The relaxed structure can be observed in the figure 3. We obtained a formation energy of 10.4 eV for the Frenkel defect. The stacking that was used is the one that minimizes its 4 formation energy .

Figure 3. Two different views of the relaxed Frenkel defect, where an interstitial defect (red) and a vacancy (blue) have been created

For the AIMD simulations, we started from the pristine system and gave 6 different kinetic energy values between 22 and 16 eV for 11 different emission angles. We do not observe the stabilization of the defect in any of them: in all cases, the displaced atom eventually returns to its original position. In order to find a possible structure that could promote the formation of the Frenkel defect, we repeated the simulations from a system in which a Stone-Wales defect has been created in the bottom layer. The two central atoms of the Stone-Wales defect are the most promising ones since they have the largest displacement from their original positions. We â&#x20AC;&#x2DC;kickedâ&#x20AC;&#x2122; one central atom with a collision energy of 18 eV (which corresponds to 90 keV of incoming electronic energy) at a given emission angle, and we observed that a Frenkel defect was stabilized. The figure 4 shows the initial system with the StoneWales defect, and the final system in which the Frenkel defect is stabilized.

Figure 4. Initial system with Stones-Wales defect (left) and the final system which contains a Frenkel In conclusion, we have observed that the defect. butterfly defect is not noticeably more stable in bilayer graphene than in monolayer and that preexisting defects (e.g. Stones-Wales) could help the creation of the Frenkel defect in bilayer graphene. The next step in the investigation of Chuvilinâ&#x20AC;&#x2122;s experiments would be to analyze if it is possible to create a divacancy in the system once the Frenkel defect is created.

References 1

Florian Banhart et al., ACS Nano 5, (2011) 26

2

J. M. Soler et al., J. Phys.: Condens. Matter 14, (2002) 2745

3

A. Zobelli et al., Phys. Rev. B 75, (2007) 245402

4

Rob. H. Telling et al., Nat. Mater. 2, (2003) 333


Tunable coupled graphene-metal plasmons in multi-layer structures at GHz and THz frequencies

AUTHORS: Alkorre Hameda , Gennady Shkerdin, Cathleen De Tandt, Roger Vounckx, Johan Stiens

Over the last few years, graphene, a mono-layer of carbon atoms tightly packed into a 2D honeycomb lattice, has rapidly become the brightest stars on the horizon of materials science and condensed-matter physics, and it has revealed cornucopia of new physics and probable applications. In recent years, an enormous interest has been surrounding the field of plasmonics, because of the variety of tremendously exciting and novel phenomena it could enable. Compared to plasmons in noble metals which have been widely studied and used, plasmons in graphene can be tuned due to the possibility of carrier density tuning in graphene by an applied electrical field, optical stimulation or chemical doping.

In this paper we investigate how one can take additional advantage of coupled metal-graphene plasmons. Hereto we derived the dispersion relation for the coupled metal-graphene plasmons in a multilayered structures. It is shown that in an optimized multi-layer structure, the coupled graphene-metal plasmon modes can depend very strongly on the electron concentration in the graphene layer. Various optimal structures with high tunability will be presented for the GHz and THz frequency range.

References [1]N. Rangel and J. Seminario, J. Phys. Chem. A 112, 13699 (2008). [2]M. Dragoman, D. Dragoman, F. Coccetti, R. Plana, and A. Muller,J. Appl. Phys. 105, 054309 (2009). [3]F. Rana, IEEE Trans. Nanotechnol. 7, 91 (2008).


NANOFILLERS FOR FOOD PACKAGING APPLICATIONS: PROPERTIES, TOXICOLOGICAL PROFILE AND CITOTOXICITY 1

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E. Araque , N. Ortuño , M. Jorda , C. Fito , S. Maisanaba , S. Pichardo , A. Jos , S. Aucejo 1 Packaging, Transport, & Logistics Research Institute (ITENE), C/ Albert Einstein,1. Parque Tecnológico. Paterna, Spain 2 Area of Toxicology, Faculty of Pharmacy, University of Seville, Profesor García González n°2, 41012 Seville. Spain Abstract. Nanocomposites are polymers reinforced using organic or inorganic nanometer-sized phase (nanofiller) which improve mechanical, thermal, barrier and other functional properties to develop innovative packaging solutions. The main goal of this work is to provide a better understanding of the relationship between some of the more relevant physical-chemical properties of nanofillers, selected according to their broadest commercial interest for application in the packaging industry, with their safety concerns and potential human hazardous effects. Emission and exposure real time measurements were performed at workplace to characterize the nanoparticle release during the processing of polymeric matrices with the studied nanofillers for obtaining the nanocomposite. Nanoparticle with lower potential hazardous effects based on its physical-chemical characterization and emissions at workplace was used as nanofillers to develop reinforced polylactide (PLA) beverage bottles with improved properties for which potential toxic effects on consumers using cytotoxicityticy biomarkers were performed. Introduction. The effects of nanomaterials on human health may be influenced by their physicochemical properties, determining the propensity of a material to generate airborne dust during its handling. The health risk potential of nanoparticles will depend on their nature, release and dispersion, magnitude and period of exposure to airborne nanoparticles, and also on exposure control in the workplace. Therefore, characterization of nanomaterials is a key issue in the health risk assessment for understanding their potential adverse effects on workers, consumers and the environment. Nanoparticles have been identified as promising materials for the reinforcement of different materials. These nanofillers are able to improve mechanical, thermal, barrier and other functional properties of packaging materials. This is of great importance especially in biopolymers, since they present insufficient properties for their application in food packaging applications. Additionally, there is another concern related with the security of the nanofillers on consumers, and a lot of research is being developed nowadays in this issue. Materials and Methods The nanofillers have been selected according their broadest applicability in the packaging industry. The selection include: a metal (Ag), a metal oxide (ZnO,) and an organoclay (ModClay, developed in ITENE). 1. Physical-chemical characterization of nanoparticles Redox potential of suspensions of nanoparticles in H2O was measured by difference of potential between two electrodes (platinum and Ag/AgCl reference electrode). All samples were at 0,1M, except ModClay, that were at 6000 ppm. 2. Measuring and monitoring of airborne nanoparticles at workplace: Measurements started with the warm-up of the twin screw extruder and continued until nanocomposite compounding was completed. Such airborne nanoparticles parameters were measured using a Condensation Particle Counter (CPC- Model 3007, TSI) in the range from 10-1000 nm, and a Philips Aerasense NP monitor (Nanotracer). 3. PLA masterbach preparation and bottle injection Different compositions of PLA masterbach were produced using PLA pellets blended with 4% of the ModClay. To produce large scale compound, a Coperion twin screw extruder DSE 20/40 equipped with a side feeder for powder dosing was used. Bottles were processed in the injection–blowing equipment. The process used to obtain the bottle consisted of one step injection-blowing procedure. Processing temperatures profile was set between 200 and 230 ºC. 4. Characterization of reinforced bottles Barrier properties of the bottles were performed following standard ASTM E96. Seven bottles were filled with 100 grams of calcium chloride, previously dried at least 4 hours at 240ºC, and were closed using the torquemeter settled at 15 lbf.in. Measurement conditions were 23ºC and 75 % relative humidity. 5. Cytotoxicity Cellular viability of the human intestinal cell line Caco-2 exposed for 24 and 48h, to the migration extract from a PLA + ModClay nanocomposite in cell culture medium was determined using MTS metabolization and Neutral Red Uptake as biomarkers. Migration extract was obtained through


commission regulation EU No. 10/2011; “plastic materials and articles intended to come into contact with food”. Results Redox potential: ModClay, with higher redox potential, is the nanoparticle with less ability to transfer electricity between the electrodes, while Ag Nanoparticles have the biggest one (Table 1). Table 1. Redox potential results in water. Samples Zinc Oxide Nanofillers (ZnO) ModClay Silver Nanoparticles (NPs)

E(V) vs Ag/AgCl in H2O 0.246 0.195 0.404 3

Quantification of airborne nanoparticles: Higher values of inhalation exposure (Number of particles/cm ) were obtained for Ag while behaviour of ZnO and ModClay were similar. Water vapour transmission rate. Results are shown in Table 2. It can be observed the difference between the raw PLA bottles and the bottles with the additive, reaching in the best case an improvement of 15%. Table 2. Water Vapour Transmission Rate Results for the PLA bottles.

Sample PLA Bottle PLA_4%ModClay

WVTR (grH2O/bottle·day) 0,070 0,062

Cytoxicity assessment Results obtained in the cytotoxicity study showed no toxic toxic effects in the Caco-2 cell line in any of the biomarkers assayed in the range of concentration tested (from 0 to 100% migration extract in cell culture medium).

Figure 2. Results from cytotoxic assay of the migration extract. Conclusions Physico-chemical characterization and workplace measurements of three nanoparticles were studied for determining as a preliminary stage the potential risk of the studied nanoparticles. ModClay presented lower values of specific surface area and redox potential in water, suggesting lower hazard risk than Ag or ZnO. Moreover, particle concentration measurements at workplace showed that local exhaustive ventilation during the studied extrusion processing of nanocomposites contributes to generate a safer workplace in the case of ModClay processing. Therefore, ModClay was selected as nanofiller for developing reinforced PLA bottles. PLA bottles showed an improvement in properties; mechanical, thermal and barrier, showing a great potential for packaging applications. Finally, cytotoxicity tests of migration extracts of ModClay bottles were tested on Caco-2cells. Results showed that studied reinforced PLA bottles presented absence or low cytoxicity. It can be concluded from the point the view of improved properties, safety at workplace, and toxicity in human cell, that ModClay is promising nanofillers for the reinforcement of food packaging materials. Acknowledgment Authors would like to thank to the MICINN (AGL2010-21210), Junta de Andalucía (AGR5969) and the European Union’s Seventh Framework Programme managed by REA-Research Executive Agency under grant agreement nº 286362 (NANOSAFEPACK Project) for the financial support. References [1]Organisation for Economic Co-operation and Development (2010). First revision of the Guidance Manual for the Testing of Manufactured Nanomaterials. ENV/JM/MONO(2009)20/REV . [2] Bickley, R., Journal of Photochemistry and Photobiology A: Chemistry, (2010), 256-260 [3] M. Jordá-Beneyto, J. Alonso, J. Salas, M. Gallur, S. Aucejo, F. Clegg, C. Breen. Proceedings of the Polymer Processing Society 24th Annual Meeting, PPS-24 (2008).


a

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M. Aresti , I.Maiza , A.Odriozola , Mª.C. Arzamendi , L.Gandía a

Cemitec, Pol. Mocholi, Plaza Cein 4, 31110 Noain, Spain maresti@cemitec.com, imaiza@cemtiec.com, aodriozola@cemitec.com b Universidad Pública de Navarra, Departamento Química Aplicada, 31006 Pamplona Abstract Printing techniques, such as inkjet technology or screen printing, have been industrialized and become an essential part of various microelectronic devices. In last years, printed electronics has emerged as a candidate for the carrying out of low cost and large area electronic systems [1]. The inkjet technology has become very attractive for the printed electronic market, but its weak spot is the lack of inks for electronic applications. This is a small market niche, however there are more and more companies working in this area. Transparent conducting oxide (TCO) is one of the most important materials to manufacture different optoelectronic devices, such as liquid crystals, solar cells and touch panels. Among these TCO materials, Indium Tin Oxide (ITO) is the most used because of its optical transparency and electrical properties [2]. In this work, a novel nanoito ink has been developed for inkjet technology (Fig.1.). A 18 wt.% of ITO ink has been formulated. In order to obtain this ink, ITO nanoparticles with 40 nm of diameter into a mixed of alcohol solvents with dispersants and binders have been dispersed for 700 minutes in a ball mill process. Since the zeta potential of ITO powder is small (usually less than 15 mV), polymer based additives have been supplied to the solution (Fig.2.). Viscosity and surface tension have been measured. The viscosity of the ink was 10-13 cp and the surface tension was 30-33 dynas/cm. The ink was stable in time (about 3 months). ITO film pattern has been printed using a piezoelectric Dimatix Galaxy inkjet printing head onto a flexible substrate (Kapton, from DuPont). ITO film was heated at a temperature of 250ºC for 30 minutes and, in order to improve electrical properties of the ITO film, a post-treatment heating at 300ºC was applied (Fig.3.). The sheet resistance was measured

by means of a four point probe technique using two NanoVolt / Micro

OhmMeter (Agilent 34411A and 34420A). The sheet resistance decreased with the second annealing, achieving 200

/sq. Also, the transmittance of the ITO film was measured using a UV-Mini 1240

Spectrophotometer (Shimadzu). The ITO film showed a high transmittance, more than 85% at 580 nm. A resistive touch panel using inkjet printing onto a flexible substrate has been prepared due to the excellent properties of the ITO film. Figure 4 and 5 show the schematic structure of the touch panel. After printing the ITO rectangles, Ag electrodes have been patterned by inkjet printing. Finally, a commercial insulator layer has been patterned onto one of the ITO layer as a separating layer. The final device showed a resistance less than 1.5 kV (Fig.6.). References [1] Young-Sang Cho, Hyang-Mi Kim, Jeong-Jin Hong, Gi-Ra Yi Sung Hoon Jang, Seung-Man Yang. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 336 (2009) 88-98. [2] Ilja Maksimenko, Michael Gross, Tobias Köninger, Helmut Münstedt, Peter J. Wellmann. Thin Solid Films 518 (2010)2910-2915.


Figures

Zeta Potential(mV) 10 Intensity

5

-200

Fig.1. Formulated Ink

0

Zeta Potential(mV)

200

Fig.2. Zeta potential of ITO nanoparticles

Fig.3. ITO thin film formed by inkjet printing

Fig.4.a) ITO pattern , b)Ag electrodes and c)insulating layer

Fig.5. Schematic of the touch screen

Fig.6. Printing touch screen onto flexible substrate


Synthesis of new nanoscale MOFs for contrast agent applications

1

Javier Ariñez,1 Arnau Carné1, Inhar Imaz1, Daniel Maspoch1,2

CIN2 (ICN-CSIC), Institut Català de Nanotecnología, Campus UAB, Bellaterra, Espanya. Institució Catalana de Recerca i Estudis Avançats (ICREA), 08100 Barcelona, Espanya.

2

javier.arinez@icn.cat, daniel.maspoch.icn@uab.es Because of its noninvasive character and its sub-millimeter spatial resolution, Magnetic Resonance Imaging (MRI) is one of the most powerful diagnosis tools in medical science4. Based on the detection of nuclear spin reorientations under a magnetic field, MRI has demonstrated to be very effective not only for the assessment of anatomical changes but also for monitoring of organ functions. However, it was also found that in some cases (e.g. gastrointestinal tract or cerebral area) the sensitivity of MRI is not sufficient. In these cases, the use of a contrast agent (CA) to enhance the image contrast is necessary. Today, CAs are used in 35 % of MRI scans. They act shortening the T1 and or T2 relaxation times of water protons, enhancing contrast between the diseased and normal tissue. To date, the major family of CAs are chelates of the highly paramagnetic Gd(III) ion, which are extensively employed in the clinical setting. However, some limitations still persist due to the low sensitivity, lack of selectivity, and low retention time that make them effective only in areas of high accumulation. To solve these problems, a common strategy consists on using nanostructures containing Gd(III) ions that provide increased in vivo circulation times and higher concentrations of Gd(III) ions per CA unit, which if targeted, yield superior MRI relaxativities. For example, Gd(III) chelates have been introduced in a variety of nanoparticle-based templates, such as nanoparticles, dendrimers, viral capsids, proteins, mesoporous silica, liposomes and zeolites.

Figure 1. (Above). Metal-organic structure resulting from the reaction of DOTP, Cu(II) and Gd(III) obtained by single crystal X-ray analysis. (Down). TEM images of the nanostructured version of this MOF. Scale bar 100 nm.

Resulting from the combination of multitopic organic ligands with inorganic cores, MetalOrganic Frameworks (MOFs) can be also excellent candidates to incorporate Gd(III) ions into extended structures.For instance, Lin et al. have used this strategy to create three dimensional (3D) MOFs containing high concentration of Gd(III) ions, which in turn have shown exceptional relaxativities rates1. To create new Gd(III)-based MOFs that could be used for


MRI, here we present a new supramolecular approach that consists on using cyclenderivate ligands (commonly used as chelating agents to design molecular CAs) to create novel MOF-based structures with promising CA properties, controllable sizes and high stabilities. These ligands present two differentiated coordination sites: i) the nitrogenated core, and ii) the pendent arms that can be functionalized with carboxylate, phosphate or N-derivative groups. These two coordination sites can serve to create bimetallic structures that incorporates Gd(III) ions, and therefore, that can act as novel multimodal contrast agents. Following this approach, in this poster we show the first synthesized MOF made of Gd(III) and Cu(II) metal ions and the cyclen-derivative ligand DOTP (Fig. 1). The obtained MOF presents a 3-D porous structure in which the Cu(II) ions are placed in the center of DOTP, coordinated by the four nitrogen atoms and a chlorine, whereas Gd(III) ions expand the structure through phosphate coordination. Significantly, this new MOF can also be synthesized at the nanoscale in the form of nanowires of less than 100 nm in length and 10 nm in diameter. These nanowires present an exceptional stability and dispersability in physiological media. In addition, they show very low toxicity and promising CA properties, making them potential candidates for a future use in MRI.

References 1. Della Rocca, J.; Liu, D.; Lin, W. Acc. Chem. Res. 2011, 44, 957-968.


Peptide functionalized magnetite nanoparticles: synthesis, characterization and magnetic behavior O. K. Arriortua, X. Lasheras, I. Gil de Muro, L. Lezama, T. Rojo, M. Insausti Dept. Química Inorgánica, Facultad de Ciencia y Tecnología, UPV/EHU, Bº Sarriena, 48940 Leioa, Spain okarriortua001@ikasle.ehu.es

In recent years there has been an important advance in the study of magnetic nanoparticles due to their application in different research fields such as biomedicine. This area has glimpsed their great potential in applications like magnetic hyperthermia, an emerging alternative for the treatment of cancer, where the size of nanoparticles, their stabilization and biocompatibility are key attributes that must be controlled. In this sense, nanoparticles must be in biological environment, requiring a proper optimization of the synthesis method and an adequate surface functionalization, which allows a good stability. Furthermore, the specificity of the nanoparticles to act only on a certain target is achieved by a proper functionalization. It has been observed in certain cases of cancer overexpress integrins

v 3

in

neoplastic cells, process known as angiogenesis. Thus, specific interactions of the cyclic peptide RGD (Arginine-Glycine-Asparagine) with integrin receptor allow selective localization of the magnetic nanoparticles in the tumor area [1]. In this sense, we present the preparation and characterization of magnetite nanoparticles properly functionalized with RGD. Fe3O4 nanoparticles have been synthesized by thermal decomposition of iron (0) pentacarbonyl. Prior to being functionalized with RGD peptide from EDC carbodiimide activation [2] these nanoparticles were transferred to water using an amphiphilic polymer shell (PMAO) [3]. The chemical, morphological and spectroscopic characterization was performed by thermogravimetric analysis, X-ray diffraction, infrared spectroscopy and transmission electron microscopy. Monosdispersed samples with sizes in the 6 to 12 nm range have been obtained with a content of organic matter that vary from one sample to another. The magnetic characterization of the samples has been performed by means of magnetization measurements and magnetic resonance spectroscopy. It has been found a superparamagnetic like behavior for most of the samples with low blocking temperatures. EMR measurements have shown a correlation between the position of geff value and the size of synthesized nanoparticles, and linewidths that vary with the size dispersion of the nanoparticles. References [1] Montet X.; Montet-Abou K.; Reynolds F.; Weissleder R.; Josephson L., Neoplasia, 2006, 8, 214-222. [2] M. De la Fuente J., Berry C., Riehle M., Curtis A., Langmuir, 22 (2006) 3286-3293. [3] Yu W., Chang E., M Sayes C., Drezek R., Colvin V., Journal of Nanotechnology, 17 (2006) 44834487.


PI-b-PMMA diblock copolymers: Nanostructure development in thin films and nanostructuring of epoxy thermosetting systems Irati Barandiaran, Arantxa Eceiza, Galder Kortaberria â&#x20AC;&#x153;Materials + Technologiesâ&#x20AC;? Group, Polytechnic School, Basque Country University, Plaza Europa 1, 20018, Donostia/San Sebastian, Spain irati.barandiaran@ehu.es A diblock copolymer is a polymer which consists of two sequences of monomer units of different chemical composition covalently bonded. Due to the thermodynamic incompatibility between the blocks, they can self-assemble in a wide variety of nanostructures because the connectivity of the blocks by covalent linkage prevents the phase separation to take place at macroscopic scale [1-2]. For nanostructuring thin films of block copolymers different techniques, such as thermal or solvent vapour annealing, graphoepitaxy or epitaxial growth, etc, can be used. On the other hand, many research studies on the formation of ordered nanostructures in epoxy thermosets containing diblock and triblock copolymers can be found in the literature [3, 4]. Interesting properties are expected in the case of composite materials based on matrices nanostructured with block copolymers that can be used for selective placement of different nanoparticles or for the generation of templates o nanopatterns. The aim of this work is, from one side, to obtain nanostructured thin films of PI-b-PMMA diblock copolymers (specified in Table 1) by both thermal and solvent vapour annealing, analyzing different morphologies obtained for different copolymer compositions and annealing methods. On the other side, the second aim is to nanostructure an epoxy thermosetting system with different Pi-b-PMMA amounts, analyzing its effect on obtained morphologies and dynamic-mechanical properties. Table 1. Diblock copolymer specification MnPI

MnPMMA

Mntot

Mw

fPI

I

A

17000

60500

77500

93000

22

1.2

B

31800

48000

79800

86200

52

1.08

Figure 1 shows morphologies obtained for copolymer A and B thin films after thermal annealing as obtained by atomic force microscopy (AFM). Copolymer A does not assemble into nanoordered morphology, microseparating into a worm-like nanostructure, without any ordered orientation. For copolymer B, a lamelar nanostructure can be observed.

Figure 1. AFM phase images of copolymer A and B thin films after thermal annealing On the other hand, for solvent vapour annealing treatment, acetone has been used as selective solvent for PMMA block. Figure 2 shows morphologies obtained for copolymer A and B thin films after solvent vapour annealing as obtained by AFM. A cylindrical morphology oriented perpendicularly to the substrate can be observed for copolymer A, where the cylinders are packed hexagonally. For copolymer B, a cylindrical nanostructure has been also


observed. If this structure is compared to the hexagonally packing structure of the copolymer A the difference is the diameter of cylinders that increases with PI content.

Figure 2. AFM phase images of copolymer A and B thin films after solvent vapour annealing On the other hand, A copolymer has also been used for nanostructuring a DGEBA/MCDEA thermosetting system. In Figure 3, morphologies obtained after curing can be seen, for different copolymer amounts.

Figure 3. Morphologies obtained for DGEBA/MCDEA systems modified with different amounts of A copolymer: (a) 0, (b) 5 wt%, (c) 10 wt%, (d) 20 wt% and (e) 30 wt%. PI-b-PMMA forms microphase-separated domains dispersed in a continuous crosslinked epoxy matrix where PMMA subchains remain miscible. The spherical-shaped micelle nanodomains are ascribed to PI chains. It has to be noted that the number and the size of spherical nanodomains, and consequently the volume fraction of the separated phase increases with increasing PI-b-PMMA content but the nanostructure does not shift from spherical micelles to any other morphology. References [1] Leibler, L.. Macromolecules, 13 (1980) 1602 [2] Bates F.S., Fredickson G.H. Annu. Rev. Phys. Chem., 41 (1990) 525 [3] Larrañaga M., Serrano E., Martin M.D., Tercjak A., Kortaberria G., de la Caba K., Riccardi C.C., Mondragon I. Polym. Int., 56 (2007)1392. [4] Serrano E., Tercjak A., Ocando C., Larrañaga M., Parellada M.D., Corona-Galván S., Zafeiropoulos N.E., Stamm M., Mondragon I. Macromol. Chem. Phys., 208 (2007) 2281.


The use of aliphatic alcohol chain length to control the nitrogen type and content in nitrogen doped carbon nanotubes a a George Bepete, Zikhona N. Tetana, Susi Lindner,b Mark H. Rümmeli,b Zivayi Chiguvarea and Neil J. Covillea a DST/NRF Centre of Excellence in Strong Materials and Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa b

Leibniz Institute of Solid State and Materials Research, P. O. Box 270116, D-01171, Dresden, Germany george.bepete@students.wits.ac.za

Abstract The nitrogen in N-CNTs can exist in a variety of oxidation states, the most important being the pyridinic type N and the quaternary N. Optimization of each type of N is important if the respective properties brought about by each type of N species are to be utilized in applications. To this end, we have synthesized a range of N-CNT materials using an ethanol/acetonitrile reactant mixture pyrolysed at different CVD synthesis temperatures and alcohol/acetonitrile mixtures with aliphatic alcohols with different chain length (ROH; R = CH3, C2H5, C4H9, C5H11, C7H15 and C8H17) to determine if the N incorporated can be influenced by temperature or oxygen content in the precursor. The C/N ratio in the precursor mixture of each different alcohol increased with increase in alcohol chain length, for example from 7.1 for a methanol/acetonitrile mixture to 12.6 for an octanol/acetonitrile mixture. XPS analysis of the CNTs produced from an acetonitrile/ethanol mixture using different CVD temperatures (700 – 1000 o C), revealed that nitrogen incorporation in N-CNTs decreased with an increase in CVD temperature and that the type of nitrogen species incorporated also varied. Molecular nitrogen and a low content of pyridinic nitrogen was obtained in N-CNTs grown at 700 oC and 800 oC, while quaternary nitrogen was noted in all N-CNTs grown. The N content in the N-CNTs grown at 850 oC increased with the alcohol chain length and also controlled the nitrogen species incorporated, an effect related to the oxygen content of the reactant mixtures. References [1] Bepete G.; Tetana ZN.; Lindner S.; Rümmeli MH.; Chiguvare Z.; Coville NJ. Carbon, 52 (2013), 316325. Figures

Nitrogen Content in N-CNT product %

1.4 1.2 1.0 0.8 0.6 0.4 0.2

0

1

2

3

4

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Aliphatic alcohol carbon chain length

Figure 1. The N composition in N-CNTs made from the different alcohol precursor mixtures obtained from XPS analysis.


(a)

Methanol/acetonitrile N1s

Quaternary 401.2 eV

408

406

404

402

400

Molecular N

Intensity (a.u.)

Intensity (a.u.)

Molecular N 404.9 eV

Ethanol/acetonitrile N1s

(b)

398

(404.6 eV)

408

406

Binding energy (eV) Butanol/acetonitrile N1s

408

406

404

Pyridinic N 398.4 eV

402

400

398

406

406

404

402

402

400

Binding energy (eV)

400

398

396

Octanol/acetonitrile N1s

(f)

Pyrrolic N 400.8 eV

Pyridinic N 398.7 eV

408

404

Binding Energy (eV)

398

Pyrrolic N 400.9 eV

Intensity (a.u.)

Intensity (a.u.)

Molecular N 404.8 eV

398

Pyridinic N 398.6 eV

Molecular N 404.8 eV

408

396

Heptanol/acetonitrile N1s

Quaternary N 401.7 eV

400

Quaternary N 401.3 eV

Binding Energy (eV) (e)

402

Pentanol/acetonitrile N1s

(d)

Quaternary N 401.2 eV

Molecular N 404.3 eV

404

Binding Energy (eV)

Intensity a.u.

Intensity a.u.

(c)

Quaternary N (401.2 eV)

396

Quartenary N 401.7 eV Pyridinic N 398.7 eV

Molecular N 404.8 eV

408

406

404

402

400

398

396

Binding energy (eV)

Figure 2. XPS N1s spectra of N-CNTs produced in CVD at 850 oC showing different types of nitrogen incorporated in N-CNTS when (a) methanol, (b) ethanol, (c) butanol, (d) pentanol, (e) heptanol, and (f) octanol were used in the precursor.


PS-b-PMMA block copolymer as template for rutile TiO2 nanoparticles L. Cano, J. Gutierrez, A. Tercjak Group ´Materials + Technologies`. Dpto. Ingeniería Química y M. Ambiente. Escuela Politécnica/Eskola Politeknikoa. Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU). Pza. Europa 1, 20018 Donostia-San Sebastián, Spain. laida.cano@ehu.es Abstract The still increasing interest of block copolymers lies in their ability to self-assemble into various 1,2 structures such as spheres, hexagonally packed cylinders and lamellae. Owing to that capability of block copolymers, they can act as template to design hybrid inorganic/organic materials with well1,3,4 organized structures. The combination of self-assembled block copolymer systems with inorganic components as different types of inorganic nanoparticles can lead to highly ordered nanocomposites 5,6 7 that have the potential to be used in a wide range of applications due to the optical, magnetic or 8-10 electrical properties of the inorganic nanoparticles. The effect of the nanoparticles on the properties of the hybrid inorganic/organic material depends strongly on the localization of the inorganic 4,11,12 nanoparticles in the polymeric matrix. In this work, an easy method of fabrication of hybrid inorganic/organic nanocomposites based on polystyrene-block-polymethyl methacrylate (PS-b-PMMA) diblock copolymer as self-assembled matrix modified with different contents of commercial, hydrophobic rutile TiO2 nanoparticles was employed. Different amounts of TiO2 nanoparticles (from 0.5 to 4 wt %) were added to the PS-b-PMMA block copolymer in order to study the effect of the TiO2 nanoparticles content on the final properties of TiO2/PS-b-PMMA nanocomposites. The final morphologies of the neat PS-b-PMMA block copolymer and TiO2/PS-b-PMMA nanocomposites and the confinement of the inorganic nanoparticles in one of the blocks of the block copolymer were studied by atomic force microscopy (AFM, Nanoscope IIIa scanning probe microscope, Multimode™, Digital Instruments). Electrical properties of obtained TiO2/PS-b-PMMA nanocomposites were studied using electrostatic force microscopy (EFM). UV-vis absorption spectroscopy (Jasco V-630) and e differential scanning calorimetry (Mettler Toledo DSC 822 ) were used for further characterization of the designed nanocomposites. As is shown in the AFM image corresponding to PS-b-PMMA block copolymer (Figure 1), a microphase separation can be easily observed in the self-assembled diblock copolymer. Bright microphase separated areas corresponded to the PS-block phase, whereas dark areas corresponded to PMMAblock phase. The addition of 0.5 wt % of TiO2 into the block copolymer did not change the final morphology of the nanocomposite if compared with the morphology of neat PS-b-PMMA block copolymer. However, when TiO2 nanoparticles were added to the block copolymer, the size of the microseparated domains increased confirming the confinement between TiO2 nanoparticles and PSblock. The introduction of more than 0.5 wt % of TiO2 nanoparticles resulted in an increase in the size of PSblock domains, which led to a significant change on the morphology from worm-like to cylindrical structure. This confirmed the location of TiO2 nanoparticles in the PS-block of the PS-b-PMMA block copolymer. The addition of 3 and 4 wt % of TiO2 nanoparticles into PS-b-PMMA matrix deteriorated the final morphology of the systems probably due to the presence of some aggregates of inorganic nanoparticles. However, all investigated nanocomposites showed good dispersion of TiO2 nanoparticles in the PS-b-PMMA block copolymer matrix independent of the content of the inorganic part. Thermal behavior of the designed materials studied by DSC confirmed that TiO2 nanoparticles were located in the microseparated PS-block domains. UV-vis spectroscopy and EFM measurements indicated that TiO2 nanoparticles transferred their optical and electrical properties to the designed TiO2/PS-b-PMMA nanocomposites.


References [1] Hamley I. W., Prog. Polym. Sci., 34 (2009) 1161-1210. [2] Darling S. B., Prog. Polym. Sci., 32 (2007) 1152-1204. [3] Weng C. C., Wei K. H., Chem. Mater., 15 (2003) 2936-2941. [4] Bockstaller M. R., Mickiewicz R. A., Thomas E. L., Adv. Mater., 17 (2005) 1331-1349. [5] Martinez-Hurtado J. L., Nanomaterials, 1 (2011) 20-30. [6] Gutierrez J., Mondragon I., Tercjak A., Polymer, 52 (2011) 5699-5707. [7] Xu C., Ohno K., Ladmiral V., Milkie D. E., Kikkawa J. M., Composto R. J., Macromolecules, 42 (2009) 1219-1228. [8] Tercjak A., Gutierrez J., Ocando C. J., Peponi L., Mondragon I., Acta Mater., 57 (2009) 4624-4631. [9] Gutierrez J., Tercjak A., Mondragon I., J. Am. Chem. Soc., 132 (2010) 873-878. [10] Peponi L., Tercjak A., Gutierrez J., Stadler H., Torre L., Kenny J. M., Mondragon I., Macromol. Mater. Eng., 293 (2008) 568-573. [11] Chang C. C., Lo C. T., J. Phys. Chem. B, 115 (2011) 2485-2493. [12] Cano L., Gutierrez J., Tercjak A., J. Phys. Chem. C, 117 (2013) 1151-1156.

Figures

Figure 1. AFM phase images (5µm x 5µm) of a) neat PS-b-PMMA block copolymer and TiO2/PS-bPMMA nanocomposites containing b) 0.5, c) 1 and d) 3 wt % of rutile TiO2 nanoparticles. The insets correspond to higher magnification AFM images (1µm x 1µm).


Arc-Discharge Synthesis of Fe@C Nanoparticles for General Applications S. Chaitoglou*, M. Reza Sanaee, N. Aguiló-Aguayo, E. Bertran FEMAN Group, IN2UB, Department of Applied Physics and Optics, Universitat de Barcelona, C/ Martí i Franquès, 1, 08028, Barcelona, Spain. The objective of the present work is to improve the protection against the oxidation, that usually appears in core@shell nanoparticles, through the control of the synthesis process. Oxidized iron nanoparticles involve a loss of the magnetic characteristics and also changes on the chemical properties. Our results indicate no loss of superparamagnetic characteristics. The reactor works in Arc-Discharge and spherical iron nanoparticles coated with a shell of carbon were obtained at near-atmospheric pressure conditions (5–8×10Pa). The current was always 40 Α and the studied concentration range of the Fe into isooctane 3 varies between 1% w/w and 4%w/w. Also the studied flow of the precursor gas varied from 30cm /min 3 to 120cm /min. The resulting diameter of the iron core is between 5-9nm as we could measure by transmission electron microscopy (TEM). From the selected area electron diffraction (SAED), the nanoparticles appear to have a crystalline dense iron core. From the energy-dispersive X-ray analysis (STEM-EDX) we have verified the absence of oxygen in the core. The magnetic properties of the nanoparticles have been investigated up to 5K temperature using a superconducting quantum interference device (SQUID). The results reveal a superparamagnetic behaviour, narrow size distribution and an average diameter of 6 nm of the nanoparticles having a blocking temperature near 40 K.

References [1] Margarethe Hofmann-Amtenbrink, Brigitte von Rechenberg and Heinrich Hofmann, Superparamagnetic nanoparticles for biomedical applications Nanostructured Materials for Biomedical Applications, 2009,121-122 [2] Mark T. Swihart,Vapor-phase synthesis of nanoparticles Current Opinion in Colloid and Interface Science 8 (2003) 127–133 [3] Nagarajan Sounderya1 and Yong Zhang, Use of Core/Shell Structured Nanoparticles for Biomedical Applications Recent Patents on Biomedical Engineering 2008, 1, 34-42 [4] http://www.wisegeek.com/what-is-a-carbon-anode.htm [5] Yoshinori Ando and Xinluo Zhao Synthesis of carbon nanotubes by Arc-Discharge method.. New Diamond and Frontier Carbon Technology, Vol. 16, No.3 2006,127-128 [6] M. Vardelle, A. Vardelle, P. Fauchais, K.-I. Li, B. Dus-soubs and N. J. Themelis, “Controlling Particle Injection in Plasma Spraying,” Journal of Thermal Spray Technol-ogy, Vol. 10, No. 2, 2001, pp. 267-28 [7]http://www.jeol.com/products/electronoptics/transmissionelectronmicroscopestem/200kv/jem2100f/ta bid/124/default.aspx [8] Subrahmanyam K S, Panchakarla L S, Govindaraj A, Rao C N R Simple method of preparing graphene flakes by an arc-discharge method. J. Phys. Chem. C, 113, 11, (2009). 4257-4259, ISSN. [9] Vladimir L. Kuznetsov, Anna N. Usoltseva, and Andrew L. Chuvilin Thermodynamic analysis of nucleation of carbon deposits on metal particles and its implicationsfor the growth of carbon nanotubes, , Physical Review Volume B 64, November 2001, 235401 10]Per Henk G. Merkus Particle Size Measurements: Fundamentals, Practice, Quality, Overview of Size Characterization Techniques ,2009,13 [11]http://serc.carleton.edu/research_education/geochemsheets/eds.html [12] Daniele Gozzi,, Alessandro Latini , Gustavo Capannelli , Fabio Canepa Myrta Napoletano , Maria Roberta Cimberle d, Matteo Tropeano, Synthesis and magnetic characterization of Ni nanoparticles and Ni nanoparticles in multiwalled carbon nanotubes, Journal of Alloys and Compounds 419 (2006) 32–39


Figures

Figure 2: TEM images of Fe@C nanoparticles in different concentrations and flows. A) 30ml/min, in a concentration of 1% w/w, B) 30 ml/min, in precursor concentration of 2% w/w, C) 30 ml/min, in a concentration of 4% w/w D) 60 ml/min, in a concentration of 1% w/w

a/a 3 30cm /min 3

60cm /min

1%w/w /σ 8.18nm/1.22(Fig 3.c)

2%w/w /σ 5.43nm/1.34(Figure 3.d)

6.23nm/ 1.47 (Figure 3.a)

6.12nm/ 1.46(Figure 3.e)

4%w/w/σ 5.34nm/ 1.33(Figure 3.f) 5.22nm/ 1.22(Figure 3.g)

3

120cm /min

5.22nm/ 1.25(Figure 3.b) Table 2: The geometric mean and the geometric standard deviation of all our samples in relation with the set parameters.

Figure 5: The energy-dispersive X-ray analysis in which we can see the pick that corresponds to the La excitation of iron and the absence of oxygen.

The hysteresis loops measured at 5K for samples with different precursor concentrations: a) 1% w/w and b) 2% w/w. Both were obtained at a precursor gas flow of 30 ml/min.

Figure 8: Zero fields cooled and the field cooled magnetization curves for 100 Oe field.


Study of thermoelectric properties of In2O3(ZnO)n and ZnO nanowires Wei-Hung Chen

(1,*)

, Yi-Chang Li

(1)

, Chuan-Pu Liu

(1)(2)

(1) Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan 70101,REPUBLIC of CHINA (2)Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, Taiwan,70101,REPUBLIC of CHINA wayhomechen@hotmail.com Abstract With the advancement of technology, the thermoelectric application of nano materials started from about 1992. The most important breakthrough came from the theory that is possible to increase ZT by using low dimensional materials predicted by Hicks and Dresselhaus [1], and the study about reducing thermal conductivity by scattering phonon between nanoscale interfaces published by R. Venkatasubramanian [2]. Based on both research and theoretical studies, there was explosive growth in the thermoelectric field of low dimensional nano materials. This study is to investigate thermoelectric properties of individual In2O3(ZnO)n nanowire, and discuss the difference between ZnO and In2O3(ZnO)n nanowires .ZnO nanowires were grown by chemical vapor deposition (CVD). In2O3(ZnO)n nanowires were synthesized by solid state reactins.[3] We deposited indium particles on ZnO nanowires by thermal evaporation and then annealed them in oxygen atmosphere at 1173 K. To measure Seebeck coefficient, single In2O3(ZnO)n nanowire was placed on a device constituting of a pair of micro-heaters with a designed circuit for sensing the temperature difference between two ends of the nanowires. Combining Seebeck coefficient with electrical conductivity measured by four probe measurement, thermoelectric power factor can be derived. Then we made MOSFET devices by electron beam lithography system to measure mobility and carrier concentration of single nanowire.The morphology and microstructure of the nanowires were characterized by scanning electron microscopy and transmission electron microscopy. The influence of microstructure, chemical composition, and carrier concentration of the In2O3(ZnO)n nanowires on thermoelectric properties is discussed. From the results, the conductivities and carrier concentrations of In2O3(ZnO)n nanowires are two order less than ZnO nanowires. And the Seebeck coefficients are three times more than ZnO nanowires.It reveals the improvement in Seebeck coefficient and the suppressing in electrical conductivity. References [1]L. Hicks and M. Dresselhaus, Physical Review B, vol. 47, 24, pp. 16631-16634, 1993. [2]R. Venkatasubramanian, Physical Review B, vol. 61, 4, pp. 3091-3097, 2000. [3]S. C. Andrews, et al., Chemical Science, vol. 2, 4, p. 706, 2011.

Figures

2 nm

Fig1. STEM image of In2O3(ZnO)n nanowire

Fig2. source-drain current to source-drain voltage characteristics of In2O3(ZnO)n nanowire


Fig3. OM image of Seebeck coefficient device

Fig4. SEM image of MOSFET device


Electrosprayed silica microspheres modified with triazine moieties for grafting on cellulosic textile 1

1

1

2

2

2

J.M. Cuevas , B.Gonzalo , C. Rodriguez , A. Dominguez , D. Galán , I. G. Loscertales * 1

GAIKER Technology Center, Ed.202, E-48170, Zamudio, Spain YFLOW S.L., Parque Tecnológico de Andalucía, C/Marie Curie 4, 29590, Málaga, Spain * Universidad de Málaga. Ingeniería Mecánica y Mecánica de Fluidos. Dr. Ortiz Ramos, s/n 29071, Málaga, Spain cuevas@gaiker.es 2

Abstract Enhancement of the competitiveness of traditional textile and clothing industry greatly depends on the ability to rapidly response to the customer requirements. The new generation of wearable articles, thus, is expanding into the promising field of multifunctional textiles characterised by added value properties and interactive features [1, 2]. In this scenario, microencapsulation has become an outstanding technology for effectively imparting new properties and related added value on textiles. Progressively, textile industry and clothing companies are experimenting with this microtechnology to produce more attractive and functional articles [3, 4]. In current research, a novel method of covalent grafting solid, hollow or core-shell sub-micronic capsules onto cellulosic fibres from well-established methods for grafting reactive dyes is presented, based on chemical functionalisation of capsule surface with highly reactive triazine moieties. For a proof of concept demonstration, silica sub-micronic spheres were developed by the electrospraying of silica sols prepared via sol-gel process from the hydrolysis of tetraethoxysilane (TEOS) [5]. The chemicalphysical properties of the spheres were characterised by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TGA) and Scanning (SEM) and Transmission Electron Microscopy (TEM). The microparticles surface was modified with chloro-triazine ligands in two-steps procedure in order to react with the hydroxyl groups in cellulose under mild conditions. As a result, the spheres were firmly anchored to the cotton yarns through the covalent bonds generated by the process herein described. Finally, it is worth mentioning that this result overcomes one of the major obstacles facing the implementation of microcapsules to textiles, that is the detachment of the capsules caused by friction, washing and use of clothes, thus opening a wide range of potential processes towards smarter functional fabrics. The authors would like to acknowledge Mr. Nicolás Campos from the University of Málaga for his help in the silica spheres production. References [1] Yufen Zhang and Dominic Rochefort, Journal of Microencapsulation, 29-7 (2012) 636-649. [2] Meritxell Martí, Vanessa Martínez, Laia Rubio, Luisa Coderch and José L. Parra, Journal of Microencapsulation, 28-8 (2011) 799-806. [3] Wang Ping, Zhao Jian-qing, Jiang Zhi-jie, Liu Yun-chun, Liu Shu-mei, Transactions of Nonferrous Metals Society China, 19 (2009) s605-s610. [4] Emily Asenath Smith and Wei Chen., Langmuir, 24-21 (2008) 12405-12409. [5] Gustavo Larsen, Raffet Velarde-Ortiz, Kevin Minchow, Antonio Barrero, and Ignacio G. Loscertales, Journal of the American Chemical Society, 125 (2003) 1154-1155. Figures

Figure 1. Picture of a compound Taylor cone from which the electrosprayed core-shell silica particles are generated.


Figure 2. Silica sub-micronic spheres manufacturated by a sol-gel electrospraying process.

Figure 3. TEM microscopy of the silica microspheres developed by electrospraying.

Figure 4. Covalent grafting of solid microspheres on cellulosic textile .


Analysis of empty states in p-type conducting nanostructured NiO thin films with tailored physical properties Domínguez-Cañizares G.1, Gutiérrez A. 1, Krause S. 2, Ovsyannikov R. 2, Abbate M.3, Díaz-Fernández D. 1, Soriano L.1 1. GRIN, Departamento de Física Aplicada and Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain. 2. BESSY II, Helmholtz-Zentrum Berlin für Energie und Materialien GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany 3. Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990 Curitiba, PR, Brazil guillermo.dominguez@uam.es Abstract Nickel oxide is an important material for several technological applications such as catalysis or gas sensing. The interaction with the surrounding environment in such devices plays an important role and the use of nanostructured materials increases the effective surface. We are able to prepare nanostructured NiO films with tailored electrical and optical properties by controlling the amount of Ni vacancies in the NiO lattice. In this work we have grown nanostructured NiO films by magnetron RF sputtering with mixed oxygenargon plasma onto alumina membranes, as well as onto several flat substrates for comparison. The NiO films grow in columns on the alumina substrates, maintaining the ordered porous structure (Fig. 1). The properties of these nanoporous NiO membranes are modulated by the oxygen content in the plasma during deposition. The electrical conductivity and the refraction index both increase by increasing the oxygen content of the plasma (Fig. 2). These changes in physical properties open new possibilities for using NiO membranes in advanced applications. In order to understand the mechanisms that lead to modify the NiO properties upon oxygen addition, it is essential to get insight into the electronic properties of the films. With this aim, we performed a near-edge x-ray absorption fine structure spectroscopy study (NEXAFS) at the oxygen K-edge of several samples grown under different experimental conditions. The measurements were carried out at the BESSY II Facility in Berlin, Germany, using the PM4-Optics and the UE52-PGM beamlines. The near edge structure at the oxygen K-edge shows the density of empty Ni d-states hybridized with oxygen p-states above the Fermi level, and it is very sensitive to chemical and structural changes [1, 2]. The presence of oxygen in the plasma during NiO growth induces an oxygen enrichment in the films, which produces Ni vacancies and, consequently, hole states of O2p character above the Fermi level [3]. The concentration of these vacancies relates to the observed change in properties. For instance, the electrical conductivity increases with the oxygen content of the films, i.e., with the density of Ni vacancies, leading to p-type conduction. The corresponding hole states must appear below the bottom of the first empty states of the conduction band, and, therefore, they should be visible at the pre-edge of the oxygen K-edge the x-ray absorption spectra. Fig. 3 shows the presence of a pre-edge feature in the O K-edge spectra of several samples with increasing oxygen content in the plasma during deposition. This pre-edge peak is absent in the stoichiometric NiO reference sample, and can only be associated with hole states produced by nickel vacancies, as suggested by its increasing trend with the oxygen content of the plasma. The thermal stability of the density of vacancies was probed by annealing the different samples in vacuum simultaneously to the x-ray absorption data acquisition. The results are shown in Fig. 4. As it can be seen, the intensity of the pre-peak decreases with temperature and time, which suggests that there is a reorganization of the NiO lattice with a consequent decrease in the density of vacancies. References [1] L. Soriano, M. Abbate, A. Gutiérrez, I. Preda, S. Palacín, J.F. Trigo, A. Vollmer, P.R. Bressler and J.M. Sanz, Physical Review B, 74 (2006) 193402-1-4. [2] I. Preda, M. Abbate, A. Gutiérrez, S. Palacín, A. Vollmer and L. Soriano, Journal of Electron Spectroscopy and Related Phenomena, 156-158 (2007) 111-114. [3] J. van Elp, H. Eskes, P. Kuiper, and G. A. Sawatzky, Physical Review B, 45, 1612 (1992).


Figures

Figure 1: SEM micrograph of NiO thin film growth on nanoporous alumina membrane

Figure 2: Resistivity of the NiO thin films with the Oxygen content in the reactive plasma

Figure 4: XANES pre-edge region of Oxygen K-edge

Figure 3: XANES spectra of Oxygen K-edge


Noelia Alvarez

Effect of size on the toxicity of gold nanoparticles (1,2) (1,2) (1,2) (1,2) , Ane Ayerdi , Leire Goikoetxea , Jaione Lorenzo , Ruben Fernandez , (1,2) (1,2) Nerea García , Ainhoa Egizabal

(1,2)

(1) TECNALIA. Mikeletegi Pasealekua 2, E- 20009 Donostia (Spain) (2) Ciber - BBN (Spain) Ainhoa.egizabal@tecnalia.com Abstract The last decade has seen an important growth in the production of nanoscale materials as a result of 1 2, 3 4 their attractiveness for a large range of applications in biomedicine , biosensing , microelectronics , 5 6,7 8,9 material engineering , energy production and environment remediation . Gold nanoparticles (AuNPs) have attracted particular scientific and technological interest due to their unique optical properties, chemical stability, easy synthesis and functionalization, all of which make AuNPs interesting candidates to use in biomedicine. However, knowledge about the health impact of gold nanoparticles is essential 10 before these nanomaterials can be used in real clinical settings . Many scientific reports have been published addressing this issue, with the goal of understanding the interactions between nanoparticles 3, 11 and cells as function of their size, shape, and surface chemistry . Although AuNPs are considered 12 inert particles and regarded as biocompatible, there are contradictory results concerning their toxicity . The goal of this work is to provide additional data on the toxic potential exerted by AuNPs of different sizes. We investigated the effects of gold nanoparticles of 5 and 20 nm on NIH/3T3 mouse fibroblast, the hemocompatibility and systemic toxicity. Finally, the biodistribution and bioaccumulation of the AuNPs in vivo into the lung, liver, spleen and kidney were examined. The cytotoxicity in NIH/3T3 mouse fibroblast cells (ATCC, CRL-1658) was determinated using MTT assay. Freshly prepared 5 and 20 nm AuNPs were dispersed in cell culture medium, diluted at concentrations from 425 µg/ml to 6.64 µg/ml and were added to cells. After 4 h of treatment, MTT assay was carried out to obtain cell viability (%). The Hemocompatibility was evaluated based on ASTM E2524-08 (Standard Test Method for Analysis of Hemolytic Properties of Nanoparticles) through a hemolysis test and an evaluation of blood coagulation. A Test for Systemic Toxicity was performance under ISO 10993-11 Standard. Fifteen Winstar Hannover female ratswere randomly divided into three groups: one control group and two experimental groups exposed to the selected nanoparticles.. Rats received intraperitoneal (i.p.) injections of 100 µL of AuNP during 6 days. Control group was treated with vehicle solution (1.2 mM sodium citrate). The body weight of the animals and their behavior were carefully recorded daily during the course of the experiment. One day after the last injection (day 7), rats were sacrificed, and the lung, liver, spleen and kidney were collected immediately. A part of the organs was stripped for histological evaluation. The remaining samples were stored at -80ºC for the quantification of gold content in each tissue though ICP-AES analysis and for the evaluation of the RNA integrity of the organs. The cell viability of 3T3 fibroblast exposed to 5 and 20nm AuNPs was higher than 80% in all of the assayed concentrations Nevertheless, the viability of 3T3 fibroblasts exposed to 5 nm AuNPs was lower. The hemocompatibility assays showed that 5 nm AuNPs had an haemolytic effect, in contrast with the 20 nm AuNPs samples. The PT and aPTT values for 5 nm and 20 nm samples were greater than reference values, indicating that samples affected the blood clotting. After testing if AuNPs treatment produces sub-acute toxicity in rats during the course of the study, we observed no mortality and no weight or any behavioral changes in the rats receiving 5 and 20 nm AuNPs.The histological evaluation of the liver tissue did not show any damage in rats exposed to 5 nm and 20 nm AuNPs. Nevertheless, ICP-AES results showed a significant increase in the amount of gold in liver and spleen after repeated injection of AuNPs in comparison with control groups.. Moreover, the bioaccumulation of gold in the organs of rats treated with 5 nm AuNPs was greater than in rats treated with 20 nm AuNPs. Finally, the values of RNA integrity number (RIN) obtained from the lung and the kidney of control rats and rats treated with 20 nm AuNPs were greater than 5, suggesting that RNA was not degraded. On the contrary, the electropherograms and RNA integrity numbers (RIN) obtained from the lung and the kidney of rats treated with 5 nm AuNPs, showed a degradation of the RNA.

References [1] Barreto, J.A., O’Malley, W., Kubeil, M., Graham, B., Stephan, H., Spiccia, L., 2011. Nanomaterials: applications in cancer imaging and therapy. Advanced Materials 23, H18–H40. [2] Rivas, G.A., Rubianes, M.D., Rodríguez, M.C., Ferreyra, N.F., Luque, G.L., Pedano, M.L., Miscoria, S.A., Parrado, C., 2007. Carbon nanotubes for electrochemical biosensing. Talanta 74, 291–307.


[3] Zhao, F., Zhao, Y., Liu, Y., Chang, X., Chen, C., Zhao, Y., 2011. Cellular uptake, intracelular trafficking, and cytotoxicity of nanomaterials. Small 7, 1322–1337. [4] Seker, U.O., Demir, H.V., 2011. Material binding peptides for nanotechnology. Molecules 16, 1426– 1451. [5] Peralta-Videa, J.R., Zhao, L., Lopez-Moreno, M.L., De la Rosa, G., Hong, J., Gardea-Torresdey, J.L., 2011. Nanomaterials and the environment: a review for the biennium 2008–2010. Journal of Hazardous Materials 186, 1–15. [6] Saunders, B.R., 2012. Hybrid polymer/nanoparticle solar cells: preparation, principles and challenges. Journal of Colloid and Interface Science 369, 1–15. [7] Valdés, Á., Brillet, J., Grätzel, M., Gudmundsdóttir, H., Hansen, H.A., Jónsson, H., Klüpfel, P., Kroes, G.J., Le Formal, F., Man, I.C., Martins, R.S., Nørskov, J.K., Rossmeisl, J., Sivula, K., Vojvodic, A., Zäch, M., 2012. Solar hydrogen production with semiconductor metal oxides: new directions in experiment and theory. Physical Chemistry Chemical Physics 7, 49–70. [8] Bootharaju, M.S., Pradeep, T., 2012. Understanding the degradation pathway of the pesticide, chlorpyrifos by noble metal nanoparticles. Langmuir 7, 2671–2679. [9] Ojea-Jiménez, I., Lopez, X., Arbiol, J., Puntes, V., 2012. Citrate coated gold nanoparticles as smart scavengers for Hg (II) removal from polluted waters. ACS Nano 6, 2253–2260. [10] Alkilany, A.M., Murphy, C.J., 2010. Toxicity and cellular uptake of gold nanoparticles: what we have learned so far? Journal of Nanoparticle Research 12, 2313–2333. [11] Lewinski, N., Colvin, V., Drezek, R., 2008. Cytotoxicity of nanoparticles. Small 4, 26–49. [12] Sperling, R.A., Rivera, P.G., Zhang, F., Zanella, M., Parak, W.J., 2008. Biological applications of gold nanoparticles. Chemical Society Reviews 37, 1896–1908.

Figures 140 5 nm

20 nm

120

Viability (%)

100

Sample

Haemolytic index (%)

Negative control

2,6 ± 1,1

Positive control

104,3 ± 3,1

AuNP-5nm

10,3 ± 1,9

AuNP-20nm

1,9 ± 1,4

80 60 40 20

*

0 425,00

212,50

106,25

53,13

26,56

13,28

6,64

C-

C+ (SDS)

Viability of 3T3 fibroblasts after 4 hours in contact with AuNP of 5 nm and 20 nm (*p<0.05)

A

MMS

Haemolytic index (%) of the AuNP samples and controls

B

C

Histological evaluation of Liver stained with haematoxilyn-eosin obtained from A) Control animal, B) Animal treated with AuNP of 5nm and C) Animal treated with AuNP of 20nm (X 40)

The research leading to these results received funding from the Basque Government under the “Programa de ayudas a la investigación estratégica- programa Etortek 2010 (IE10-276), BIOMAGUNE'10” project


Enhance fluorescence efficiency of dye/clay hybrid films by the co-adsorption of surfactants. Nerea Epelde Elezcano, Virginia Martínez-Martínez, Iñigo López Arbeloa Departamento de Química Física, Universidad del País Vasco UPV-EHU, Spain Nerea.epelde@ehu.es The encapsulation of photoactive molecules in constrained media is of a great technological interest. The matrix not only increases the thermal and photo-stability of the organic guest but also can modify the final photophysical properties of the organic guests embedded. Moreover, many of the photonic and optoelectronic applications of photofunctional host/guest materials require also the development of macroscopic ordered arrangements. In this sense, layered clay minerals are attractive host materials a well-organized 2D multilayer structure can be easy obtained by elaborating supporting films [1]. In this contribution, Pyronine Y (PY) dye is intercalated at different loadings in supported thin films of Laponite clay (Lap), a synthetic clay mineral with a very small particle size (≈ 30 nm). The intercalated dye molecules are with a preferential orientation respect to the normal axis of clay film providing a macroscopic ordered system. The orientation of dye molecules respect to the normal to the clay surface can be determined by means of the anisotropic response of the hybrid films to the plane of the polarized light [2]. However, experimental results suggest that as the dye loading increase, molecules tend to aggregate in H-type geometry (face-to-face stacking) in the interlayer space of the clay. Generally, these aggregates are characterized by blue-shifted absorption band respect to the monomer (Figure 1) but also they are efficient quenchers of the fluorescence reducing drastically the emission efficiency of the final hybrid system [3]. Surface modifications of clay (organophilic clays) with surfactant alkylammonium ions (C12TMA) is a good strategy to improve the general fluorescence capacity of dye molecules in clay systems, maintaining the macroscopic orientation of the dye [4]. Thus, systematic varying surfactant concentrations and the procedure to co-incorporate with the PY dye into the clay interlayer space, dye aggregation on the Lap films was reduced. In those cases an increase of around 6 times in the fluorescence efficiency has been detected (Figure 2).

References [1] a) A.Ceklovsky,S.Takagi, J.Bujdak, J.Colloid. Interf. Sci, 360 (2011) 26-30. b) J.Bujdak, A.Czimerova, N. Iyi, Thin. Solid. Films. 517 (2008) 793-799. c) M. Roulia, A.A. Vassiliadis, Micropor. Mesopor. Mat. 122 (2009) 13-19. [2] V. Martínez, F. López, J. Bañuelos, I. López. Chem. Mater, 17 (2005) 4734. [3] a) K. Meral, N. Yilmaz, M. Kaya, A. Tabak, Y. Onganer, J. Lumin. 131 (2011) 2121-212. b) M. Arik. Y. Onganer, Chem. Phys. Lett. 375 (2003) 126-133. [4] S. Salleres, F. López Arbeloa, V. Martínez, C. Corcóstegui, I. López Arbeloa, Mater. Chem. Phys. 116 (2009) 550-556.


Figures

fluorescence intensity (u.a)

normalize absorbance

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aggregate band

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450

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aggregate band 550

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[Figure 1]. a) Absorption b) Fluorescence spectra of Py/Lap films at different loadings.

550

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wavelength (nm) [Figure 2]. Fluorescence efficiency of a Py/Lap films with different surfactant loading.


Highly monodisperse spindle-like calcium hydroxyapatite and fluoroapatite nanoparticles for biomedical applications Alberto Escudero,1 Jesús M. de la Fuente,2 and Manuel Ocaña1 1. Instituto de Ciencia de Materiales de Sevilla. CSIC – Universidad de Sevilla. Calle Américo Vespucio 49. E-41092 Seville, Spain. 2. Instituto de Nanociencia de Aragón, Universidad de Zaragoza, Calle Mariano Esquillor s/n, E-50018, Zaragoza, Spain. aescudero@icmse.csic.es http://colmat.icmse.csic.es/ Abstract Calcium phosphate nanostructures are attracting great interest in nanomedicine in both colloidal state, due to their applications in transfection, gene silencing, drug delivery and imaging techniques [1], and bulk systems (i.e. bioactive coatings, cements, and nanocrystalline bulk synthetic ceramics for bone tissue engineering) [2-3]. This is explained for its high biocompatibility and good biodegradability. In fact, calcium phosphate is the inorganic mineral of human bone and teeth [4]. In general terms, most of these applications require uniform nanoparticles or nanostructures with controlled size, shape, composition, surface chemistry, and other physicochemical properties [5]. A high colloidal stability is also required in case of the dispersed systems. This is normally achieved after an appropriate functionalization process, which also provides anchors for adding functional ligands such as antibodies, peptides, proteins, and some anticancer drugs [6].

We report the synthesis of highly monodisperse calcium hydroxyapatite and calcium fluoroapatite nanoparticles functionalised with poly(acrylic acid) (PAA) which exhibit a new spindle-like morphology. The nanoparticles are synthesised through a one-pot microwave-assisted hydrothermal method from aqueous basic solutions containing calcium nitrate, sodium phosphate monobasic, and PAA, as well as sodium fluoride in the case of the fluoroapatite particles. The size of the nanospindles is 142 (26) × 28 (4) nm for calcium hydroxyapatite (Figure 1A) and 160 (14) × 40 (5) nm for calcium fluoroapatite. Both apatite-based nanoparticles show negligible toxicity for Vero cells (Figure 1B) and a very high (up to at least one week) colloidal stability in 2-(N-morpholino)ethanesulfonic acid (MES) 50 mM at pH 6.5 (Figure 2A), which is a commonly used buffer for physiological pH. As a result of their formation mechanism, which consists of an aggregation process of smaller subunits, the nanoparticles show high specific surface area (85 m2 g-1). This makes them suitable for targeted drug delivery systems. In addition, the particles can be made luminescent by doping with Eu3+ (Figure 2B) so that they can be used as biolabels. It is also shown that the luminescence is more efficient for the fluoroapatite particles than for the hydroxyapatite, which is attributed to the presence of OH– quenchers in the latter. All these features make both kinds of apatite-based nanoparticles promising tools for biomedical applications.

References [1] Epple, M. et al., J. Mater. Chem., 20 (2010) 18−23. [2] Kalita, S.J. et al., Mater. Sci. Eng. C, 27 (2007) 441–449.


[3] Champion, E. Acta Biomater., 9 (2013) 5855–5875. [4] Dorozhkin, S. V., and Epple, M., Angew. Chem., Int. Ed., 41 (2002) 3130−3146 [5] Xia, Y. N., Nat. Mater., 7 (2008) 758−760. [6] Thanh, N. T. K., and Green, L. A. W., Nano Today, 5 (2010) 213−230.

Figures

Figure 1A: TEM micrograph of highly monodisperse calcium hydroxyapatite nanospindles functionalised with PAA. Figure 1B: Viability assays performed with Vero cell line for PAAfunctionalised calcium hydroxyapatite nanospindles at different nanoparticle concentrations.

Figure 2A: Size distributions determined by DLS for PAA-functionalised calcium hydroxyapatite suspensions in MES 50 mM at pH 6.5 after different aging times. Figure 2B: Emission spectra (λex= 393 nm) of aqueous suspension of PAA-functionalised Eu-doped hydroxyapatite (EuHAp, blue line) and fluoroapatite (EuFAp, red line) nanospindles. The inset shows the red luminescence of suspensions of both europium-doped nanophosphors when irradiated with UV light.

More details can be found in Alberto Escudero et al., Langmuir, 29 (2013) 1985−1994. http://pubs.acs.org/doi/abs/10.1021/la304534f


Morphological and optical properties of Cu2O nanostructured thin films 1)

1,2)

3)

3)

1)

Carole Fauquet , Artak Karapetyan , Anna Reymers , Vladimir Gevorgyan , Suzanne Giorgio , 1) 1) Serge Nitsche , Wladimir Marine 1) Aix Marseille Université, CNRS, CINaM UMR 7325, 13288, Marseille, France 2) Institute for Physical Research of NAS of Armenia, Ashtarak-2, 0203, Armenia 3) Russian-Armenian (Slavonic) University, 375051, H.Emin st.123, Yerevan, Armenia fauquet@cinam.univ-mrs.fr

Abstract Cuprous oxide (Cu2O) is a p-type metal oxide semiconductor with a direct forbidden band gap of about 2.17eV. Cu2O electronic structure is of considerable interest for large range of applications. Several interesting properties of this material are related to its rich excitonic structure and to the fact that the binding energy of the excitons is relatively large (140 meV for the threefold degenerated orthoexciton state [1]). As the exciton binding energy in Cu2O is quite large, it is reasonable to assume that the excitons can play a main issue in transport and recombination mechanisms. Photoluminescence (PL) in the visible - near infra red spectral range is generally observed at low temperature in bulk, crystalline and polycrystalline Cu 2O films [2,3]. In this communication we report on the optical properties of nano-crystalline cuprous oxide (Cu2O) thin films formed by thermal 0

0

oxidation of copper thin films at two different temperatures 800 C and 900 C. Samples exhibit nanocrystalline structure with typical nano-crystal size of about 2-30 nm as observed by High Resolution Transmission Electron Microscopy. The optical absorption coefficients of both films at room temperature were obtained from an accurate analysis of their transmittance and reflectance spectra. We demonstrate the different contributions due to direct and indirect transitions of the various exciton states in the optical absorption. Photoluminescence (PL) spectra of Cu2O were then recorded versus photoexcitation wavelength by using continuous-mode lasers at 325nm, 473nm and 532nm with various output powers. In the photoluminescence spectra we observe the near infrared band with a clearly well resolved peak at 1.34eV (923nm), a large visible band at 1.88eV (660nm) and luminescence at 1.97eV (630 nm). The observed PL near infra red band (1.34eV) and the band 1.88eV are below the band-gap transition of thin films (2.11eV). Therefore the observed luminescence evidently involves impurities or defect levels like Cu and oxygen vacancies. However, the luminescence band 1.97eV is due to phonon-assisted recombination of the 1s orthoexciton in both film series. We also investigated the optical properties of this last peak (1.97eV) arising from non-resonant two-photon excitation by a femtosecond pulse laser. All PL measurements were performed at room temperature. Finally, the origin of this room temperature PL is discussed. References [1] D. W. Snoke, A. J. Shields, and M. Cardona, Phys. Rev., 45,(1992),11693. [2] J. Bloem, A. J. Van der Houven van Oordt, and F. A. Kröger, Physica, 22, (1956), 1254. [3] H. Solache-Carranco, G. Juárez-Díaz, A. Esparza-García, M. Briseño-García, M. Galván-Arellano, J. Martínez-Juárez, G. Romero-Paredes, R. Peña-Sierra, J. Lumin., 129, (2009),1483.


Boltzmann and quasiballistic transport mean free paths in disordered nanowires with anisotropic scattering J. Feilhauer1,2, J. J. Sáenz1 and M. Yépez1 1

Condensed Matter Physics Department and Centro de Investigación en Física de la Materia Condensada (IFIMAC), Universidad Autónoma de Madrid, Fco. Tomás y Valiente 7, 28049-Madrid, Spain 2 Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 84104-Bratislava, Slovakia juraj.feilhauer@savba.sk

Abstract We study an electron transport in the disordered mesoscopic nanowires with length L which contain randomly distributed anisotropic scatterers. The aim of this paper is to show that the transport mean free path ℓ in the quasiballistic regime (where L < ℓ ) can be significantly smaller than the mean free path in the diffusive regime (where ℓ << L << ξ and ξ is the localization length). For simplicity we demonstrate our calculations for the case of coherent electron transport in the quasione-dimensional (Q1D) disordered wires made of a two-dimensional conductor but our results are more general and similar behavior should be also observable in the three-dimensional wires and electromagnetic waveguides. In the rectangular Q1D wire with the width W the electron wave is quantized in the transversal direction and electrons at the Fermi energy occupy the discrete energy transversal states known as energy channels. To simplify the calculations we assume that the electron wavefunctions satisfy a periodic boundary conditions in the transversal direction. For the large number of channels N our calculations are independent on the choice of boundary conditions and holds also for the hard-wall boundaries. The transport properties of disordered wire are determined by the channel transmissions Tn – the probabilities that the electron impinging the disordered wire in the channel n is transmitted through the wire [1]. The transport properties depend strongly on the microscopical realization of disorder therefore it is useful to study the disorder-averaged values <Tn>. In the quasiballistic regime the disorder is weak and transport can be treated perturbatively (one can neglect the multiple scattering). The channel transmissions decays linearly with length as <Tn> = 1 – L/ℓnQB, where ℓnQB is the quasiballistic mean free path of the channel n [2]. The total mean free path in the quasiballistic regime is then ℓQB = [ (1/N) ∑1/ℓnQB ]-1, where N = 2W/λF is the number of occupied channels and λF is the Fermi wavelength [3]. In the diffusive regime the multiple scattering dominates the transport and the channel transmissions scale as <Tn> = ℓnD/L , where ℓnD is the diffusive mean free path of the channel n [1]. The total diffusive mean free path reads ℓD = (1/N) ∑ℓnD . If the scatterers are isotropic then ℓnQB = ℓnD which yelds ℓQB ~ ℓD. Does these formulas hold also for the wire with anisotropic scatterers? To answer this question we calculate analytically the transport mean free paths in the quasiballistic (ℓQB, ℓnQB) and diffusive (ℓD, ℓnD) regime using the perturbative [2] and Boltzmann approach [3]. The analytical derivation can be performed in the limit of infinite number of channels N where instead of discrete index n we label the channels by the continuous angle θ = asin(n/N). Then ℓnQB → ℓQB(θ) and ℓnD → ℓD(θ). The angle θ = 0 corresponds to the electrons that move in parallel with the wire edges and emulate the electrons impinging perpendicularly to the sample. The anisotropic scatterers are modeled as a cylindrical potential barriers with radius a and height U which we treat in the Born approximation. Such scatterers are radially symmetric which implies that the scattering rate depends only on the angle α between the direction of the incident and outgoing electron wave. Our results are shown in the figure 1. The graphs a) and b) show the ratios ℓD(θ = 0)/ℓQB(θ = 0) and ℓD/ℓQB as the functions of a/λF. The other graphs show the scattering rate and ratio ℓD(θ)/ℓQB(θ) for four selected values of a/λF. If the scatterer is almost point-like (a/λF << 1) the scattering rate is isotropic (independent on α) and as expected ℓnQB = ℓnD and ℓQB ~ ℓD. With the increasing radius a the anisotropy increases and the electrons are scattered mostly forwardly to the small angles. For a/λF ~ 1 the quasiballistic mean free path of normal incidence ℓQB(θ = 0) is about three times larger than the diffusive one ℓD(θ = 0). On the other hand the total mean free path in the quasiballistic regime ℓQB is much smaller then the diffusive one ℓD and this difference can be of the order of magnitude. Our calculations confirms that the mean free paths in the wire with anisotropic scatterers (with enhanced forward scattering) can strongly depend on the wire length.


References [1] S. Datta, Electronic Transport in Mesoscopic Systems, (Cambridge University Press, Cambridge, UK, 1995). [2] P. A. Mello and S. Tomsovic, Phys. Rev. B, 42 (1992) 15963. [3] J. Feilhauer and M. Moško, Phys. Rev. B, 83 (2011) 245328. [4] M. Cahay, M. McLennan and S. Datta, Phys. Rev. B, 37 (1988) 10125. Figures

Fig. 1: a) The ratio between the mean free path of the normal incidence in the diffusive ℓD(θ = 0) and quasiballistic ℓQB(θ = 0) regime as a function of the parameter a/λF. b) The ratio ℓD/ℓQB between the transport mean free paths in the diffusive and quasiballistic regime as a function of a/λF. c)-f) The scattering rate as a function of the scattering angle α. g)-j) The ratio ℓD(θ)/ℓQB(θ) between the diffusive and quasiballistic channel mean free paths as a function of the channel angle (angle of incidence) θ. The graphs c)-j) correspond to the four selected values of a/λF written in the legend.


Aerosol Casted Metal Organic Frameworks. A Complete Study from Meso to Microscale. a,b

a

b,c

a

Alfonso Garcia Marquez , Patricia Horcajada , David Grosso, Gérard Férey, Christian a b,c b,c Serre, Cédric Boissiere and Clément Sanchez. a

Institut Lavoisier de Versailles, UMR CNRS 8180, Université de Versailles Saint-Quentin, 45 avenue des États-Unis 78045. Versailles, France. Fax: +331 3925 43 02; Tel:+331 3925 4407. b UMR CNRS 7574 Chimie de la Matière Condensée de Paris. Collège de France, Université Paris 06CNRS. 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France Fax: +331 4827; Tel: +331 4827. alfonso-ramon.garcia-marquez@uvsq.fr Abstract Metal Organic Frameworks (MOFs) and Porous coordination polymers (PCP) are type 2 hybrid 2 -1 3 -1 materials presenting a large porosity (SBET up to ~ 6000 m g ; Vp ~ 3.0 cm g ) as well as easy tuneable topology and composition. Such family represents a plethora of useful compounds for catalysis, separation science or biomedicine. Usual synthetic methods employed for such compounds are solvo/hydrothermal synthesis, microwaveassisted solvothermal [1], microfluidics [2], ionic liquids, sono-[3], mechano-[4] and electro-chemistry [5], as well as spray drying [6]. The latter, a typical sol-gel synthesis and processing method, allows a lower cost and environmentally friendly continuous-production alternative to the currently employed batchsynthesis. As a main advantage, the versatility of the industrial device allows obtaining a MOF or PCP from either 1 or 2 different precursor solutions. This fact allows control of the reaction time and stoichiometry avoiding rapid completion particularly when the precursors are very reactive. In this work, three benchmarked MOFs: HKUST-1, ZIF-8 and MIL-100(Fe) polymorph Fe3(BTC)2 were synthesized via this spray casting method from two separated solutions injected at the same rate into a hot air flow. The aspect of the three product was micrometric diameter hollow spheres, some of them (HKUST-1 and ZIF-8) were constituted of nanocrystals. Some of the activated products presented competitive space time yields with respect to the commercial values reported for the corresponding Basolite analogues. In a second time, Fe3(BTC)2 like PCP were also synthesized via a template approach using two surfactants: non-ionic Pluronics F-127 and anionic cetyltrimethylammonium bromide (CTAB). The resulting template-assisted PCPs presented hollow sphere shapes and specific 2 -1 surfaces of 600 and 1010 m g .for F-127-templated PCP and CTAB-templated PCP, respectively, (Figure 1). Finally, the two template assisted Fe3(BTC)2 compounds were synthesized at nanoscale using a homemade spray drying device. The obtained particles showed diameters ranging within the nanosubmicronic range. Moreover, CTAB-templated Fe3(BTC)2 presented hierarchically formed spherical pores (Figure 2) attributed to a phase separation between the surfactant and the Fe3(BTC)2. A final comparison about the shape differences between the micrometer sized and the submicrometric sized spheres related to the drying process of both devices is also discussed. In conclusion, this work represents a complete study of aerosol synthesized MOFs and PCPs from the nanometric to the micrometric scale. The space time yields of some of them place this method as a fair alternative to the current batch production of these porous solids.

References [1] Seo, Y.-K.; Hundal, G.; Jang, I. T.; Hwang, Y. K.; Jun, C.–H; M Chang, J.–S. Microp. Mesop. Mater. 119 (2009) 331-337. [2] a) Witters, D.; Vergauwe, N.; Ameloot, R.; Vermeir, S.; De Vos, D.;Puers, R.; Sels, B.; Lammertyn, J. Adv. Mater. 24 (2012) 1316-1320. b) Falcaro. P.; Buso, D.: Hill. A.J.; Doherty, C. M. Adv.Mater. 24 (2012) 3153-3168. [3] Thompson, J. A.; Chapman, K. W.; Koros, W. J.; Jones, C. W.; Nair, S.; Microp. Mesop. Mater. 158 (2012) 292-299. [4] Klimakow, M.; Klobes P.;Thunemann A. F.; Rademann, K.; Emmerling, F. Chem, Mater. 22 (2010) 5216-5221.; idem. Microp.Mesop.Mater. 154 (2012) 113-118; Yuan, W. B.; Garay, A. L.; Pichon, A.; Clowes, R.; Wood, C. D. CrystEngComm. 12 (2010) 4063-4065. [5] Li, M. Y.; Dinca, M. J. Am. Chem. Soc. 133 (2011) 12926-12929. [6] Carné-Sánchez, A.; Imaz, I; Cano-Sarabia, M.; Maspoch, D. Nature Chem. DOI: 10.1038/nchem.1569. Garcia Marquez, A ; Horcajada, P.; Grosso, D.; Férey, G.; Boissière, C.; Sanchez, C. Chem. Commun. (2013), Accepted.


Figure 1. Nitrogen sorption isotherms of activated template synthesized PCPs.

Figure 2. Transmission electron microscopy (SEM) image of CTAB-templated Fe3(BTC)2.


Versatile Bionanostructured Materials via Direct Reaction of Functionalized Catechols Beatriz Garcíaa, Javier Saiz-Poseua, Josep Sedób, Jordi Hernando,c Felix Busquéc and Daniel RuizMolinab a

Fundación Privada ASCAMM, Unidad de Nanotecnología (NANOMM), ParcTecnològic del Vallès, Av. UniversitatAutònoma, 23 - 08290 Cerdanyola del Vallès, Spain b

Centro de Investigación en Nanociencia y Nanotecnología, Campus UAB, 08193, Cerdanyola del Valles,Spain.

c

Chemistry Department, Universitat Autònoma de Barcelona, Campus UAB 08193, Cerdanyola del Vallès, Spain

e-mail: bgarcia@ascamm.com

Wettability is a fundamental property of solid surfaces governed by both the chemical composition and the surface topographic microstructure. Thus, to obtain highly hydrophobic surfaces, many methodologies based on, for instance, fluorinated materials, and control of surface microstructure have been developed. However, most of these methodologies involve thermal treatments, surface patterning, or the use of sophisticated deposition techniques, such as chemical vapor deposition, enhanced plasma vapor deposition, self-assembly and spin coating. Regarding practicality, costeffectiveness and scalability, such elaborate treatments are often inadequate. In order to obtain both water and oil repellent properties, there still exists the challenge to develop methodologies for fabricating materials relying on operationally simple procedures. Nature can be a good source of ideas to design and develop such novel functional materials. This is the case of coatings bio-inspired on mussel adhesion proteins containing catecholic (L-DOPA) residues, shown to adhere very strongly to virtually any surface. Inspired by this natural system, in this work catecholic polymers with one or two unsubstituted (fluoro) alkyl chains in the aromatic ring have been used to generate surface-coating materials under alkaline conditions. These materials convey oleo/hydrophobic properties to different kinds of surfaces by means of robust coatings of nanometric thickness that are effective over a large range of surfaces and materials -nanostructured or otherwise-. Herein we report a new approach for the preparation of catechol-based materials based on a simple polymerization process in the presence of ammonia in a way reminiscent of melanization reactions. This strategy represents a significant advance in combining many advantages: ease of preparation, solubility in appropriate solvents and a high ratio of adhesive (catecholic)-to-functional moieties. When the material resulting from the reaction of functionalized catechol with ammonia is dissolved in non-polar solvents such as hexane, robust coatings on a representative variety of substrates, both at the nano-/macroscale are obtained, by means of a quick and ex situ approach without any pretreatment or modification. Whereas catechol monomers bearing a long alkyl chain afford coatings with a persistent hydrophobic character, it was shown that this methodology can be extended to several other catechols with different ring pendant groups, providing varied surface functionalities such as oleophobic/hydrophilic, anti-fouling, anti-bacterial activities and water remediation. On the other side this material is shown to spontaneously structure in the form of nanoparticles a few hundred nanometers in diameter in water, which easily stick to polyester fibers affording stable NP coatings.


References [1] J. Sedó, J. Saiz-Poseu, F.Busqué, D. Ruiz-Molina, Adv. Mater., 25 (2013), 653-701. [2] J. Saiz-Poseu, J. Sedó, B. García, C. Benaiges, T. Parella, R. Alibés, J. Hernando, F. Busqué, D. Ruiz-Molina, Adv. Mater., 2013, DOI: 10.1002/adma.201204383.   Figures

Figure 1. Water droplets on polymer- coated glass (left) and polyester (right).

Figure 2. Catechol nanoparticles attached to a fiber.


Fine-Tuning of Fluorescence Resonance Energy Transfer Efficiency into Zeolite L nanochannels L. Gartzia-Rivero, J. Bañuelos-Prieto, I. López-Arbeloa Dpto Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV-EHU), Aptdo 644 48080, Bilbao, Spain leire.gartzia@ehu.es One of the most fascinating topics of the modern photochemistry is the design of nanostructured artificial photonic systems capable of harvesting and transporting the light to the reaction center and with the desired energy (mimicking the natural process of photosynthesis) [1]. The incorporation of organic photoactive guests into one-dimensional channel materials, such as Zeolite L, gives rise to well organized multifunctional dye-doped hybrid materials. The rigid environment of the solid host protects the organic molecule against chemical or photochemical attacks and increases its thermal resistance. Moreover, geometrical constrains imposed by the framework lead to a supramolecular organization of the guests into the channels, with a preferred orientation along the zeolite L channels. Nowadays, there is a wide variety of commercially available laser dye families that emit in the ultraviolet (UV), visible (Vis) and near-infrared (IR) regions susceptible to be located by their size in nanoporous materials. In these sense, doping the host’s channels with different fluoropohores leads to a hybrid ordered antenna systems for light-harvesting (Figure 1). In these systems light from the UV/Vis/NearIR is harvested and transported to the desired reaction center with the adequate energy via successive energy transfer processes [2]. However, it still remains a challenge to organize multiple cromophores with well-defined interchromophore distances and control their relative orientations and the exact ratio of donors to acceptors, which are the key factor that determine the efficiency of FRET (Förster resonance energy transfer). The present work deals about the development of antenna devices where laser dyes (C165 and DMPOPOP in the blue region, BODIPYs in the green-yellow and Oxazines in the red) are allocated into the zeolite L nanopores, an alluminosillicate with one-dimensional channels running along the crystal and a pore diameter of about 7.1 Ǻ. The pores of the host are filled with a high amount of dyes, exclusively in monomeric form and aligned in a preferential orientation, thus giving rise to an organized photoactive material (Figure 1). The obtained organized dye-doped material has been fully characterized by several photophysical techniques: steady-state, time-resolved and confocal fluorescence microscopy. The intermolecular energy transfer between dyes takes place into zeolite L channels directly from donor excited molecules to an acceptor unexcited neighbor, via FRET mechanism, or after energy migration among the donors. In order to control the efficiency of the energy transfer process we have combined different dyes together with a fine selection of their relative proportions. Just modifying both parameters, the energy transfer efficiency can be maximized favoring the red emission (antenna system), or alternatively the FRET can be partial, reaching a tunable emission in the blue, green and red regions (white-light emitting devices) [3] (Figure 2).

References [1] P. K. Dutta, R. Varghese, J. Nangreave, S. Lin, H. Yan, Y. Liu, J. Am. Chem. Soc., 133 (2011) 11985-11993. [2] G. Calzaferri, R. Méallet-Renault, D. Brühwiler, R. Pansu, I. Dolamic, T. Dienel, P. Adler, H. Li, A. Kunzmann, J. Am. Chem. Soc., 12 (2011) 580-594. [3] L. Gartzia-Rivero, J. Bañuelos-Prieto, V. Martínez-Martínez, ChemPlusChem, Vol 77, 1 (2012) 61-70


Figures

Figure 1. Nanostructured antenna system based on Zeolite L channel filled with different fluorophores.

WHITE LIGHT

EMISSION TUNING

Figure 2. Normalizad time-resolved emission spectra of C165, PM546, Ox4 doped zeolite L, together with the fluorescence images under 350/50 nm excitation and emission recorded with different band passes (400 nm, 515 nm, 580 nm and 665 nm respectively).


(Two page abstract format: including figures and references. Please follow the model below.) Polymers-grafted particles nanocomposites : dynamic contribution of grafted chains on dispersion mechanisms and mechanical properties Nicolas Genevaz

,1,2*

2

2

2

1

, Denis Bertin , Didier Gigmes , Trang Phan ,François Boué , Jacques Jestin

1

1

2

Laboratoire Léon Brillouin, CEA Saclay 91191 Gif-sur-Yvette, France Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, Av. Esc. Normandie Niemen, 13397 Marseille Cedex 20 nicolas.genevaz@cea.fr

Abstract     For most practical applications, the incorporation of nano-filler has been found to dramatically enhance the mechanical properties of polymeric materials. Understanding the reinforcement mechanism of nanoparticles filled polymers matrix is of critically importance from industrial (for tire industry or food packaging) to fundamental point of view. Reinforcement in nanocomposites depends of two major effects : fillers network contributions and chains – fillers interactions which can not be easily separeted. We are interested in elucidating the mechanisms of mechanical reinforcements in model nanocomposites especially by dissociating the role of the filler from the one of the polymer chains dynamic. Thanks to controlled “grafting from” polymerization process, we can synthesis well defined grafted nanoparticles with a controlled length -1 (Mn=25000 g.mol ) that can be mixed with free polymer chains to form nanocomposites by solvent casting. The particle dispersion inside the polymer matrix can be easily tuned with the grafted to free chain ratio R that enables us to obtain different morphologies, form the individual particle dispersion for R>0.24 to the formation of dense large aggregates with intermediate interconnected particle networks for R<0.24 [1] (Figure 1). The grafted chain conformation is also depending of these different dispersion states, stretched for individual dispersion, the grafted brushes collapsed when particles forms aggregates [2]. With specific chain labelling, we recently show with mean square displacement (MSD) (Figure 2) measurements that a positive shift of the Tg of the grafted brushes is also associated with the formation of the aggregates meaning that the chain dynamic is modified by the particles organization. The reduction of the chain mobility with the particle dispersion is currently under validation with additional neutron spin echo measurements and can thus be discussed precisely as a function of the rheological behaviour of the nanocomposites. References [1] Chevigny, C. et al., Macromolecules, 43 (11), (2010), 4833–4837. [2] Chevigny, C. et al., Macromolecules, 44 (1), (2011), 122–123. Figures


Particle charge electrically and optically measured - an analysis of efficiency Hanno Wachernig, Clemens Helmbrecht Particle Metrix GmbH, Neudiessener Str. 6, D-86911 Diessen, Germany wachernig@particle-metrix.de Abstract The knowledge of the electrostatic interface charge potential known as zeta potential (ZP) is important for the functionalization of particles and for the control of the affinity of surfaces to particles and macromolecules. The ZP measurement via an optical electrophoresis set-up is well known but can become a tedious task, as zeta potential as a single point parameter is not sufficient for the understanding of new formulations. The presence of polyelectrolyte, salt concentration and pH have influence on the ZP, making titrations necessary in order to get a reliable charge finger print. In optical electrophoresis, such charge titrations require external sample mixing and subsequent long equilibration times for each titration step before the sample can be measured. Due to the time consumption (~1h) and complexity of titrations, such studies were either performed by random sampling or even omitted. The presented oscillating streaming potential (OSP) method offers an electrical signal pick-up, which releases particle interface potentials within seconds. As the titrand solution is mixed into the sample beaker directly, titrations are finished in minutes (fig. 1). All in all, the efficiency of the OSP method invites to do charge measurements and titrations. Opposite to conventional techniques, the sensitivity of the OSP method is high for nano-particles and polyelectrolytes which are frequently used in coat surfaces. The sensitivity of OSP can be explained by the increased specific surface compared to microparticles. An example of protein titration is demonstrated in figure 2. The extension of the working range to polymer solutions closes an important gap in colloid science. Due to lack of sensitivity, such measurements are not possible with optical zeta potential measurement methods. Combined with a dynamic light scattering sensor the OSP procedure offers the determination of the specific surface charge [C/m²]. Charge and size measurements exhibit a large working range in size and concentration, <1 nm up to 6.5 ¾m and 0.001% v/v to 40% v/v, respectively, making OSP a flexible technique suitable for a broad range of applications.


Fig. 1: Principle of efficiency: Oscillating streaming potential between the pick-up electrodes. The signal is generated from ions at the interface of particles immobilized at the Teflon measurement cylinder. The signal is instant and responds immediately (in s) to the addition of titrand solutions.

Fig. 2: pH charge titrations on 1 nm BOVE albumin and 5 nm OVE albumin over the isoelectric point (IEP). The concentration of the samples was 1%. One titration took less than 10 minutes.


Magneto-Optical Magnetometry of cobalt nano-structures grown by focused electron beam induced deposition 1

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O. Idigoras , E. Nikulina , P. Vavassori , A. Chuvilin , and A. Berger

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CIC nanoGUNE Consolider, Tolosa Hiribidea 76, 20018 Donostia-San Sebastian, Spain Ikerbasque, Basque Foundation for Science, Alameda Urquijo 36-5, 48011 Bilbao, Spain oidigoras@nanogune.eu

Reduction of ferromagnetic system sizes is a key research area in the field of magnetism and of crucial importance for a wide range of technological applications, such as, high-density hard disk drive storage [1] and spintronics [1,2]. Continuously increasing demands on these technologies are pushing nanofabrication into the extreme nanoscale regime. Even though structuring of nanoscale systems may be achieved by different lithography techniques [3], focused electron beam induced deposition (FEBID) of magnetic materials has recently attracted a very substantial amount of interest [4,5]. One of the most attractive features of this technique is the rapid prototyping, because it is a one-step technique. Moreover, FEBID allows for the fabrication of 3-dimensional complex nanostructures and even lateral dimensions below 1 nm have been demonstrated. In this work, we have fabricated several Co structures by means of EBID, including wires where lateral dimensions were shrunk down to 30 nm and 3 dimensional nano-pillars. Their magnetic properties have been measured by means of a magnetooptical Kerr effect (MOKE) microscope [6], which allows in plane as well as out of plane magnetic property studies. Moreover it is able to characterize individual structures. TM

TM

FEBID of Co structures have been performed using a commercial Helios NanoLab DualBeam system (FEI, Netherlands). Figure 1 (a) shows a scanning electron microscopy image of a 30 nm wire, while figure 1 (e) displays an array of pillars that are 80 nm wide and 210 nm high. In order to get the right composition, lateral resolution and desired shape of the structures one needs to find the optimal deposition parameter conditions. In this case, both structures were made at constant values of -5 background pressure (6x10 Pa), pitch (5 nm) and sample to gas injection system distance (50 µm). While the 30 nm wide wire was produced using a high electron beam energy of 30 kV, an electron beam -5 current of 2.7 nA and 6x10 Pa precursor gas pressure, the nanopillars were obtained by using an -4 electron beam energy of 2 kV in conjunction with an electron beam current of 86 pA and 8x10 Pa precursor gas pressure.

The magnetic analysis was carried out with an optical wide-field polarization microscope optimized for Kerr microscopy (Evico Magnetics GmbH, Germany). The microscope is equipped with a high sensitivity 2 CCD camera that is capable of taking magnetic-contrast images of 25x20 µm sample surface areas. Area that is divided in 1024x768 pixels. The key feature of our approach is that we can measure the field dependent local magnetization, either in-plane or out-of-plane, by selecting an arbitrary (shape, size, and position in the field of view) region of interest (ROI) on the CCD camera pixel array, and use this array selection as a conventional light intensity detector. In this way, we can maximize the magnetooptical difference signal ΔI/I0 for opposite magnetization states, resulting in an increase of the signal-tonoise (S/N) ratio. The advantage of our approach is evident from the measurement reported in Fig. 1(b), where we demonstrate that we are able to record a single shot hysteresis loop with an average S/N of 4.1 per data point for a 20 nm high Co wire that is only 30 nm wide (Fig. 1 (a)) using a ROI of 340 x 8 pixels. Renormalizing this result to the commonly used detection criterion (S/N =2) [7], we conclude that -15 2 our measurements are sensible to a magnetic moment of only 2 x 10 Am . By comparing our results to other magnetometry techniques such as the latest generation SQUIDs with their sensitivity in the 10 12 -13 2 - 10 Am range it becomes obvious that MOKE microscopy based magnetometry allows for true nanoscale magnetic characterizations. Figure 1 (c) shows an average over 9 single shot measurements for the 30 nm wide wire. Here, we find that the S/N has increased by a factor of almost 3. This confirms that we may be able to measure even smaller structures with less than 10 nm width. Having a look to the 30 nm wide wire magnetization reversal hysteresis loop, one observes a rectangular hysteresis loop with a coercive field of 75 mT (Fig. 1 (c)), i.e. the expected behaviour given that the external field is applied along the wire length, which is the easy axis of magnetization due to shape anisotropy. For wider wires (not shown here) more complex hysteresis loops have been observed were the magnetization reversal is not given anymore by a single switch, but instead double jump inversion is observed. In the case of hysteresis loops measured in a periodically ordered 20 x 20 nanopillars (Fig. 1 (e)), a center-pinched structure is found with reduced magnetization in remanence state and with a magnetic


plateau at low applied fields, i.e. features that arise due to large magnetostatic coupling between adjacent pillars, while exchange coupling is low or absent. Our results demonstrate that the combination of FEBID and MOKE microscopy makes it possible to explore magnetization reversal properties of individual as well as more complex collective nanostructures and thus opens up a broadly applicable avenue to perform systematic research on nano-scale magnets. We acknowledge the financial support from FEI Company (Netherlands).O. I. acknowledges Basque Government fellowships No. BFI09.284.

References [1] C. Chappert, A. Fert and F. N. Van Dau, Nature Mater. 6 (2007) 813. [2] S. D. Bader and S. S. P. Parkin, Ann. Rev. Cond. Matt. Phys. 1 (2010) 71. [3] M. Geissler and Y. Xia, Adv. Materials 16 (2004) 1249. [4] G. Boero, I. Utke, T. Bret, N. Quack, M. Todorova, S. Mouaziz, P. Kejik, J. Brugger, R. S. Popovic and P. Hoffmann, Appl. Phys. Lett. 86 (2005) 042503. [5] L. Serrano-Ram贸n, R. C贸rdoba, L. A. Rodr铆guez, C. Mag茅n, E. Snoeck, C. Gatel, I. Serrano, M. R. Ibarra and J. M. De Teresa, ACS Nano 5, (2011) 7781. [6] E. Nikulina, O. Idigoras, P. Vavassori, A. Chuvilin and A. Berger, Applied Physics Letters 100, (2012) 142401. [7] D. A. Allwood, G. Xiong, M. D. Cooke and R. P. Cowburn, J. Phys. D: Appl. Phys. 36, (2003) 2175. Figures

Figure 1: (a) and (d) show scanning electron microscope images respectively of a 30 nm wide Co wire and an array of nanopillars of size 80x210 nm, both of which are fabricated by electron beam induced deposition. (b), (c) and (e) display hysteresis loops measured in these structures by Kerr effect microscopy. While (b) and (c) show hysteresis loop measured in 30 nm wide Co wire ((b) is a single shot measurement and (c) an average of 9 loop cycles), (e) shows hysteresis loop measured in the Co nanopillar array.


Efficient Electrodes for Applications in Dielectric Elastomer Actuators: Carbon Nanotubes vs Graphite Laura J. Romasanta, Miguel Ángel Lopez-Manchado, Raquel Verdejo Instituto de Ciencia y Tecnología de Polímeros ICTP-CSIC, Juan de la Cierva 3, Madrid, Spain laura.jimenez@ictp.csic.es, lmanchado@ictp.csic.es, rverdejo@ictp.csic.es

Abstract Over the past decade, fundamental and technological interest on “smart materials” has dramatically grown due to their capacity to respond to a variety of external stimuli (temperature, light, pH, magnetic, electric fields...). One of the most attractive applications is based in the development of actuators, or “artificial muscles”, able to reversely transform electrical energy 1

into mechanical work . Soft dielectric elastomer actuators (DEAs) are progressively emerging as strong candidates due to their toughness, lightness, easy processability and generally low cost. DE actuators are basically compliant variable capacitors. They consist of a thin elastomeric film coated on both sides with compliant electrodes. When an electric field is applied (see Fig.1), the electrostatic attraction between the opposite charges on opposing electrodes and the repulsion of the like charges on each electrode give rise to an electrostatic 2

pressure which forces the DE to contract in thickness and expand in area . This electrostatic compressive stress

Where

is given by:

is the dielectric permittivity of vacuum (8,85 x 10

permittivity of the DE and

-12

F/m),

is the relative dielectric 3

is the applied electric field across the electrodes .

Looking at the expression derived by Pelrine et al., it is obvious to think that an increment in the charge stored by unit of area of the electrodes will increase the compressive stress, thus increasing the strain suffered by the DE. Although during the past years research effort has been focused in the development of the right elastomers, compliant electrodes are also fundamental to DEAs development. The ideal electrode material must: i) Be low-cost and easy to fabricate, ii) maintain uniform contact over the entire active region of the elastomer in order to


ensure an homogeneous electric field during the electro-mechanical actuation and iii) deform with the dielectric elastomer without generating an opposing stress or losing conductivity. The principal aim of this work is to study the role of different carbonaceous particles as compliant electrodes in a PDMS based actuator (see Fig.2). More specifically, graphite powder and carbon nanotubes are here evaluated with respect to their conductivity in order to achieve optimum strain and efficiency for a given electric field. The results obtained show that the higher conductivity of the carbon nanotubes here employed leads to a substantial increment in the actuation strain percentages compared to graphite. References 1. Bar-Cohen, Y., Electroactive Polymer (EAP) Actuators as Artificial Muscles. Reality, Potential and Challengues. SPIE Press: Bellingham, Washington DC, 2001. 2. Carpi, F.; Gallone, G.; Galantini, F.; De Rossi, D., Enhancing the dielectric permittivity of elastomers. In Dielectric Elastomers as Electromechanical Transducers. Elsevier: Amsterdam, 2008; pp 51-68. 3. Pelrine, R.; Kornbluh, R.; Pei, Q.; Joseph, J. Science 2000, 287, (5454), 836-839. Figures

Fig 1. Squematical view of DEA operating principle

Fig 2. Graphite (left) and Carbon Nanotubes (right) as compliant electrodes


Long range effects on quantum conductance of screw-like doping in N doped carbon nanotubes H. Khalfoun*, P. Lambin and L. Henrard Physics Department (PMR), University of Namur, B-5000 Namur, Belgium (*) Permanent address: LPTPM, Faculty of Sciences. Hassiba Benbouali University, 02000 Chlef, Algeria hafid.khalfoun@fundp.ac.be Abstract Long-range electronic effects in doped 2D graphene have been highlighted on the STM images and on the density of states close to the Fermi level in ordered and disordered systems [1]. Here, the consequences of long-range interference effects on 1D carbon nanotubes are investigated. In that perspective, the quantum electronic transport properties of Nitrogen (N) doped carbon nanotubes are studied in the Landauer-Buttinger approach within the tight-binding approximation [2-5]. First, resonance states are shown to appear at given energies depending on the periodicity and on the number of periods, even for distant dopant. Two classes of universal transmission responses are observed depending on the periodicity. They are related to the appearance (or not) of an electronic gap for infinite systems around the defect band. More precisely, the quantum conductance drops to one quantum conductance plateau when the distance between the dopant is three times the period of a pristine armchair nanotube, demonstrating a standing waves behavior of the electronic states associated with the electron transport.

For other periodicity, no conductance is observed at the

energies of the electronic state localized on the defect.

Second, a screw configuration is considered for the position of the dopant, around the nanotube, i.e. the defects are regularly rotated from one period to the other. We found that the quantum conductance depends on the rotation angle between the defects and that, for given angles, screw-like configuration has no effect on the transport properties. Moreover, rotational disorder does not change the quantum conductance scheme within a few classes of screw angles.

References [1] P. Lambin, H.Amara, F.Ducastelle and L.Henrard, Phys. Rev.B 86 (2012) 045448 [2] S. Latil, S. Roche, D. Mayou and J.C. Charlier, Phys. Rev. Lett. 92 (2004) 256805 [3] C. Adessi, S. Roche and X. Blase, Phys. Rev. B 73 (2006) 125414 [4] R. Avriller, S. Roche, F. Triozon, X. Blase and S. Latil, Modern Phys. Lett. B 21 (2007) 1955 [5] H. khalfoun, P. Hermet, L. Henrard and S. Latil, Phys. Rev. B 81 ( 2010 ) 193411


Oxide-oxide composites based on nanopowders functional application T. Konstantinova, F. Glazunov, I. Danilenko, O. Gorban Donetsk Institute for Physics and Engineering named after O.O.Galkin, NASU, 72 R.Luxembourg st., Donetsk 83114, Ukraine matscidep@aim.com Abstract Modern technical progress requires the creation of nanocomposites based on oxide matrix with oxide filler that can be used in various fields of engineering. In present report we obtained and use nanopowders based on ZrO2 -3 mol% Y2O3, La0.7Sr0.3MnO3 and NiO nanoparticles for creation of magnetic composite for optoelectronic and radioelectronic and for SOFC electrons material. Nanopowders of (Zr,Y)O2, LSMO were synthesized by co-precipitate method with calcination change of reagent precipitator in ensure synthesis of LSMO allows to exclude bimodal distribution of particle size to monomodal one. Composites obtained by mixing of different of different nanopowders with subsequent sintering. Organic pore formed polymethylmethacrylate (PMMA) was used for creation of predetermined porosity of composites. Magnetic composites It has been shown [1] that tape casting technology allows to produce magnetic nanocomposite films of micrometer thickness. The investigation of the morphology of the green film dried at 30ºC shows that the film has a homogeneous structure made from globules of up to 500 nm in size (Figure 1). Analysis of magnetization curve show that transition from the state with main value of magnetization to saturation condition occurs with sufficiently low expenditure of energy of environmental. Material of SOFC anode Modern construction of SOFC consists of two, air and fuel, porous ceramic electrodes and oxygen ion conducting ceramic electrolyte sandwiches between them. These electrode materials must have suitable chemical compositions, sufficient porosity (about 40%) and strength, high number of reaction zones and good catalytic activity. To obtain good electrochemical properties, it is desirable that SOFC components were prepared from nanoparticles [2-3]. TEM image of the mixture of ZrO2 and NiO powder calcined at 800ºC is shown in Figure 2. According to XRD and TEM data, both oxides have cubic lattices. Their size depends on calcination temperature as shown in Table 1. Table1. Particle size (nm) of ZrO2, NiO and LSM oxides at different calcination temperature (according to XRD) T,ºC 700 800 900 1000 1100 1200 ZrO2 16 21 29 39.8 61 95 NiO 39 52 65.8 70.4 112 150 LSM 20 35 54 60 85 100 NiO-ZrO2 anode composites were reduced in flow of hydrogen 200 cm3/min at 400-800ºC during 2 hours. Composites sintered from powders calcined at 700 and 1000ºC had 6 and 9% porosity, respectively. The reduction of these samples was not full at named conditions. The full reduction in flow of hydrogen occurred at 800ºC only for powders calcined at 1200ºC ensuring high porosity in NiO-ZrO2 composite. Material of SOFC cathode The growth of ZrO22 and LaSrMnO3 nanoparticles (Figure 3) was observed when calcination temperature was increased (Table 1). At sintering at 1300ºC, porosity of sintered cathode electrode was 0.8% (with no pore former) and 13% (with 10% PMMA). The porosity increases with decreasing of temperature to 1150ºC and was 25% and 45% with no pore former and with it, respectively [3-4]. Acknowledgment This work is supported by the projects #38-12 of Program of NASU “Hydrogen in alternative energy and new technologies”.


References [1] V.A.Lubenets, I.L.Lyubchanskii, O.A.Gorban, V.V.Burkhovetskii, E.A.Dvornikov, G.K.Volkova, I.A.Danilenko, MPMNSâ&#x20AC;&#x2122;10- abstracts, (2010) 142-143 [2] T.E.Konstantinova, I.A.Danilenko, N.P.Pilipenko, A.Dobrikov, Electrochemical Society Proceedings, 2003-07 (2003) 153-159 [3] F.I.Glazunov, I.A.Danilenko, T.E.Konstantinova, V.A.Glazunova, G.K.Volkova, V.V.Burhovetsky, International Conference on Oxide Materials for Electronic Engineering (OMEE-2012)- abstracts, (2012), 291-292 [4] I.A.Danilenko, T.E.Konstantinova, V.N.Krivoruchko, G.E.Shatalova, G.K.Volkova, A.S.Doroshkevich, V.A.Glazunova, Full Cell Technologies: State and Perspectives, Springer, (2005), 245-251 Figures Figure 1. Structure of film based on La0.7Sr0.3MnO3 and ZrO2-3mol%Y2O3 nanopowders

b

a

c

Figure 2. Structure of nanopowders ZrO2-8mol%Y2O3, NiO and LSMO for SOFC anode and cathode

a

b

Figure 3. Strength of anode material vs porosity (a) and strength of cathode material vs sintering temperature (b)


Nanoparticle Monolayers of Iron Oxide Fabricated using Electrophoretic Deposition: A New Path to Superlattices? 1,2

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Alex J. Krejci , Kevin G. Yager , Chris Ruggiero , Adriana Mendoza-Garcia , Shouheng Sun , and 1,2 James H. Dickerson 1 Deparment of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, VU Station B #351807, Nashville, TN, USA 2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA 3 Department of Chemistry, Brown University, Providence, RI 02912 alex.j.krejci@vanderbilt.edu Abstract Nanoparticles (NPs) are known to display properties that differ distinctly from their bulk counterparts. Also, ensembles of NPs are known to exhibit collective properties, which differ from the characteristics of an individual NP. A few examples demonstrate this fact quite clearly. In one example, CdSe NP arrays were created. Ordered arrays, unordered arrays, and a system of isolated particles were studied for their optical properties. Measurements of the optical properties exposed a pronounced 1 enhancement in the sharpness of the photoluminescence peak for in the ordered array of NPs . In another example, the electrical properties of Ag NPs were measured for two-dimensional arrays that were hexagonally packed NPs and cubically packed NPs and compared to the electrical properties of individual NPs. The electrical properties measured in all three cases were dramatically different simply 2 due to the change in geometry of the NP system . In a final example, arrays of Ag NPs were created and then sintered. By sintering ordered arrays, the researchers were able to create large monocrystals 3 of silver, which were not created with unordered arrays . These are just three examples that elucidate the power that can be achieved by obtaining control of order within NP ensembles. In this presentation, we will begin by discussing a new technique we have developed for making two-dimensional assemblies of NPs, or nanoparticle monolayers (NPMs) (Figure 1a). The NPMs are fabricated using electrophoretic deposition (EPD) (Figure 2). EPD is a rapid, safe, and facile process for depositing suspended nanomaterials onto large substrates. In the discussed work, for example, we 4 fabricated homogeneous NPMs on 1 cm X 4 cm silicon wafers with only one minute of deposition . Beyond this, the substrate could be easily scaled to make even larger films if desired. EPD is also very versatile in the materials that can be used. To date, we have fabricated NPMs composed of monodisperse iron oxide, titania, and CdSE NPs. However, we expect other materials can easily be assembled into NPMs with little change in the current technique. Next, because we know that order is so important in these films, we will discuss statistical methods by which we have been able to measure and enhance ordering within iron oxide NPMs. We 5 created Voronoi tessellations based on scanning electron microscope images of the NPMs (Figure 1b). Using the tessellations and particle locations, we quantified order using three previously developed statistical quantities. Additionally, we developed a fourth measure of order, which is designed to detect anisotropy in particle-particle bond orientations. With these measures of order we detected changes as small as 5% in the ordering. With these tools, we intend to understand the mechanisms that create ordering within the NPMs as well as the variables that affect ordering. Then, given the precision by which we can analyze the films and the knowledge of how to vary the ordering, we can attempt to fine tune the ordering and potentially fine tune the properties of the NPMs. Inspired by work done on block copolymer ordering, we choose to first study the changes in 6 order that can be controlled by varying the geometry of the substrate on which the NPs are deposited . Substrate geometry is manipulated by using electron beam lithography to create rectangular elements 7 arranged in hexagonal arrays (a framework) . We studied multiple frameworks with various scales and orientation of rectangular elements. By using the statistical tools discussed above, we have analyzed the ordering from the various framework designs and observed that the framework of certain sizes and orientations can indeed affect ordering within the NPMs. To date, substrate geometry has been our major focus, however many other variables such as NP surfactant, solvent, deposition rate, etc., can just as well be studied using the statistical tools we assembled. Additionally, the tools can be applied to other monolayer fabrication processes such as Langmuir-Blodgett, evaporative self-assembly, spin coating, etc. The main limitation of these statistical measurement tools is that one must be able to locate each particle within the film. However, given the ability of current imaging techniques (TEM, SEM, AFM, etc), this is easily overcome for most twodimensional samples. Thus, we will discuss a highly versatile technique for fabricating NPMs and additionally introduce a set of tools that can precisely measure order in NPMs fabricated using virtually any process. References


[1] Zaitseva, N.; Zu Rong Dai; Leon, F. R.; Krol, D., Journal of the American Chemical Society, 29 (2005) 10221-10226. [2] Taleb, A.; Silly, F.; Gusev, A. O.; Charra, F.; Pileni, M. P., Advanced Materials, 9 (2000) 633-637. [3] 907.

Courty, A.; Henry, A. I.; Goubet, N.; Pileni, M. P., Nature Materials, 11 (2007) 900-

[4] Krejci, A. J.; Gonzalo-Juan, I.; Dickerson, J. H., ACS Applied Materials & Interfaces, (2011) 3611-3615. [5] Krejci, A. J.; Thomas, C. G. W.; Mandal, J.; Gonzalo-Juan, I.; He, W.; Stillwell, R. L.; Park, J.-H.; Prasai, D.; Volkov, V.; Bolotin, K. I.; Dickerson, J. H., The Journal of Physical Chemistry B, (2012) [6] Bita, I.; Yang, J. K. W.; Jung, Y. S.; Ross, C. A.; Thomas, E. L.; Berggren, K. K., Science, 5891 (2008) 939-943. [7]

Krejci, A. J.; Mandal, J.; Dickerson, J. H., Applied Physics Letters, 4 (2012) 043117.

Figures

Figure 1: (a) SEM image of an NPM composed of 9.6 nm diameter, spherical, iron oxide NPs. The monolayer is not completely filled in, thus regions of substrate are visible (b) Voronoi tessellation plotted over SEM image of NPs. The neighbors for each particle share a Voronoi edge. The number of neighbors of each particle is indicated by the color of the cell. (Regions of substrate are excluded from the tessellation and shown in black.)

Figure 2: Schematic of electrophoretic deposition. Two electrodes are inserted into a suspension of particles. An electric field applied between the two electrodes draws the charged particles toward the electrodes.


Synthesis and magnetic properties of Nickel Ferrite nanoparticles for biomedical applications X. Lasheras, O.K. Arriortua, M. Insausti, I. Gil de Muro, T. Rojo, L. Lezama Dpto. Química Inorgánica, Facultad de Ciencia y Tecnología, UPV/EHU, Bº Sarriena, 48940 Leioa, Spain xabier.lasheras@ehu.es Magnetic nanoparticles and their corresponding specific properties are becoming an important investigation area in last years. The size confinement to nanometer scale in magnetic materials changes the properties from those of the bulk ferro and ferrimagnetic counterparts, the remainder magnetization disappears keeping the magnetic moment. These properties are interesting for some biomedical applications, such as drug delivery, MRI contrast and magnetic hyperthermia. In order to enhance magnetic hyperthermia, nanoparticle average sizes, crystalline anisotropy and magnetic moment are important factors to be considered. The most usual materials for such applications are superparamagnetic iron oxide (SPIO) compounds. A good approach to increase the magnetic moment is to introduce paramagnetic atoms in the crystal structure, replacing some of Fe(II) cations in octahedral holes [1]. These cations cause a decompensation of ferrimagnetic structure increasing the net magnetic moment and magnetic permeability. What´s more, changes in crystalline anisotropy are also expected [2]. In this work we report the preparation and characterization of nickel ferrites varying nickel composition in the 3 – 20% range, in order to study the effects in magnetic behavior. The nickel ferrite nanoparticles have been synthesized by polyol method, using nickel(II) and iron(III) acetylacetonates as precursors, 1,2-hexadecanediol as dispersant, benzyl ether as solvent and oleic acid and oleylamine as coating agents. For one of the samples, seed mediated growth process was performed to evaluate changes in magnetic properties with nanoparticle size [3]. X Ray Diffraction (XRD) technique was used to corroborate the inverse spinel structure without impurities for synthesized samples. Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM) studies have shown that the diameter of ferrite nanoparticles is around 10-14 nanometers for non-grown particles. Inductively Coupled Plasma (ICP) spectroscopy has been used to determine the exact percentage of Nickel on samples. Finally, the mass percentage of organic material was obtained by thermogravimetic (TG) measurements under Argon atmosphere. In order to study the magnetic behavior of the different samples, magnetization measurements were carried out in function of magnetic field at 300 K, as well as Electron Magnetic Resonance Spectroscopy (EPR) measurements at room temperature in noninteracting dispersed particles. This characterization, has led us to understand the relationship between magnetic response and nickel percentage in the ferrite inverse spinel structure and EMR signals have been related to the size of the nanoparticles. In this sense, a displacement of the signal to higher g eff values have been observed for increasing sizes. References [1] Shouheng Sun, Hao Zeng, David B. Robinson, Simone Raoux, Philip M. Rice, Shan X. Wang, Guaxiong Li, J. Am. Chem. Soc, 126 (2004) 273-279. [2] Seung-hyun Noh, Wonjun Na, Jung-tak Jang, Jae-Hyun Lee, Eun Jung Lee, Seung Ho Moon, Yongjun Lim, Jeon-Soo Shin, Jinwoo Cheonn, Nano Lett., 12 (2012) 3716-3721. [3] Jongnam Park, Eunwoong Lee, Nong-Moon Hwang, Misun Kang, Sung Chul Kim, Yosun Hwang, Je-Geun Park, Han-Jin Noh, Jae-Young Kim, Jae-Hoon Park, Taeghwan Hyeon, Angew. Chem, 117 (2005) 2932-2937.


Magnetic, electrical and magneto-transport thin nanohole arrays grown on flat anodic aluminum oxide templates 1

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3

D. C. Leitao , J. Ventura , C. T. Sousa , J. M. Teixeira , J. B. Sousa , S. Pinto , J. M. Michalik , 4 5 3,6,7 4 1 M. Jaafar , A. Asenjo , .J M. De Teresa , M. Vazquez , and J. P. Araujo 1

INESC-MN and IN, Rua Alves Redol 9, 1000-029 Lisboa, Portugal IFIMUP and IN, Departamento de Física e Astronomia, Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre, 678, 4169-007, Porto, Portugal 3 Laboratorio de Microcopias Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, E-50018 Zaragoza, Spain 4 Departamento de Física de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, Spain 5 Instituto de Ciencia de Materiales de Madrid CSIC, E-28049 Madrid, Spain 6 Instituto de Ciencia de Materiales de Aragon (ICMA), CSIC—Universidad de Zaragoza, E-50009 Zaragoza, Spain 7 Departamento de Física de la Materia Condensada, Universidad de Zaragoza, E-50009 Zaragoza, Spain

2

dleitao@inesc-mn.pt Abstract The introduction of voids into a thin film significantly alters the characteristics of the medium, leading to exotic and interesting physical properties. In fact, such voids can lead to quantum effects in the conductivity, enhanced optical transmission, artificial vortex pinning sites in superconductors and magnonic crystals, facilitating research and technological applications. In particular, the inclusion of micrometer or nanometer sized artificial defects in magnetic materials is an effective way to engineer the corresponding physical properties. At present the main stress is put on the study of nanohole arrays of nanometer dimensions (inter-hole distances and hole diameter sub micrometer range), which magnetic properties (domain morphology and reversal processes) are very distinct from micrometer-period structures. However the main challenge still lies in the fabrication of nanometer scale nanohole structures. On the one hand one can take advantage of well established nanofabrication processes like electron-beam litpgraphy and litf-off, focused-ion-beam processing and deep ultraviolet methods. On the other hand, the bottom-up approach offers self-assembling procedures. One reliable method arises from the use of anodic aluminum oxide (AAO), which provides a simple and low cost route to fabricate tailored nanometric dimensions. In the present contribution we show the results of an extensive study of the magnetic, transport and magnetotransport properties, including Hall effect measurements of NiFe nanohole arrays with thickness ranging from 2 to 100 nm, ion beam sputtered on top of AAO templates. Atomic Force Microscopy images show the replicated AAO hexagonal pattern when a 25 nm thick NiFe film is deposited on top (see figure 1a and 1b respectively). By correlating magnetic (see figure 2) and magnetotransport (see figure 3) properties of nanohole arrays we detect a strong dependence on the film thickness (t) and therefore the morphology. For small t a granular-like film is formed. With increasing t morphological percolation occurs and the Tunneling Magnetoresistance contribution decreases together with apparition of the bulk-like behavior and Anisotropic Magnetoresistance contribution. The latter one becomes dominant for even bigger film thickness. Using a simple and straightforward low-incidence-angle ion-milling process it was also possible to significantly reduce the particular topography of AAO, showing a major impact on the physical properties of nanohole arrays grown on top and to achieve high-quality thin-NhA films with well controlled morphology. One may thus provide nanostructured magnetic materials with engineered physical properties and give the potential for further technological advances in magnetic sensing and storage. References [1] D.C. Leitao, J. Ventura, C.T. Sousa, J.M. Teixeira, J.B. Sousa, M. Jaafar, A. Asenjo, M. Vazquez, J.M. De Teresa and J.P. Araujo, Tailoring the physical properties of thin nanohole arrays grown on flat anodic aluminum oxide templates, Nanotechnology, 23 (2012) 425701 [2] C. Leitao, J. Ventura, J.M. Teixeira, C.T. Sousa, S. Pinto, J.B. Sousa, J.M. Michalik, J.M. De Teresa, M. Vazquez and J.P. Araujo, Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays, J. Phys.: Condens. Matter 25 (2013) 066007


Figures

Figure 1. AFM images of the (a) as-grown AAO substrate and (b) 25 nm thick NiFe nanohole array.

Figure 2. Room temperature M(H) curves for nanohole arrays and corresponding continuous thin films with t = 2 nm (thin), t = 30 nm (intermediate) and t = 100 nm (thick). Note the distinct magnetic field magnitudes of the nanohole and thin film samples.The and Ç symbols correspond to the direction of H relative to the growth-induced axis.

Figure 3. MR curves at 100 K for selected nanohole arrays with t = 2, 6 and 100 nm, measured in the longitudinal (Ç ) and transverse ( geometries. The insets show details near Hsw (switching field).


Surface effects in formation and application nanoparticles based on zirconia 1

2

2

3

2

O. Myloslavskyy , I. Danilenko , I. Yashchishyn , S. Lyubchik , T. Konstantinova 1

Donetsk National University, 24 Universitetskaya st., Donetsk 83000, Ukraine Donetsk Institute for Physics and Engineering named after O.O.Galkin, NASU, 72 R.Luxembourg st., Donetsk 83114, Ukraine 3 Instituto de Soldadura e Qualidadem, Taguspark - Oeiras, Av. Prof. Dr Cavaco Silva 33, 2740-120 Porto Salvo, Portugal matscidep@aim.com Abstract 2

Oxide nanopowders based on zirconia have attracted in the last time researchers and manufacturers due to high progress in technology of nanopowder production. Zirconia nanopowders are used in catalysis, thermal barrier coating, SOFC components, drag delivery and markers in medicine, microelectronics and wide variety of applications in composite nanoparticles and ceramic nanocomposites. In present report we will discuss effect of nanoparticles surface in two variants of nanopowder composition: 1) ZrO2-3mol%Y2O3 (ZYC00); 2) ZrO2-3mol%Y2O3 + 0.3...3% Cr2O3 (ZYCxy). At first we describe surface effects in the process of hydroxide-oxide transformation and nanoparticles growth during calcination in yttrium stabilized zirconia (ZYCoo). In the second variant of nanopowders the role of chromium oxide in change of surface state of nanoparticle is analyzed. Nanopowders of zirconia hydroxide were prepared by co-precipitation technique. Mixed together water solutions of high purity ZrO(NO3)2 and Y(NO3)3 salts taken at stoichiometric composition (3 mol% Y2O3) were used as starting materials. The hydroxide precipitates were dried with using pulse magnetic and microwave fields. Nanopowders were calcined in the temperature range of 350-1000ºC. Nanoparticles obtained by our technology are single crystals with soft and easily destroyed agglomerates. They have low degree of dispersion (<20%) and homogeneous dopants distribution and are 100% tetragonal. The morphology of these nanopowders and the structure of initial xerogel are shown in Figure 1. On the base of analysis of nanopowder structure by TEM and HRTEM it was found that the growth process of nanoparticles synthesized by co-precipitation has three stages (Figure 2): cooperativeoriented crystallization of ordered areas in xerogel polymer matrix and disintegration of crystallized areas (350–400ºC); oriented attachment of particles into single crystal caused by electrostatic interaction (400–600ºC); attachment of particles to single and poly-crystals by oxygen diffusion through vacancies in surface layers of joining crystals (600–1,000ºC). These phenomena should be treated from the mesoscopic point of view as they attributed to the interaction of groups of particles between each other. Proposed conception on mesoscopic processes of nanoparticles formation makes the understanding and theoretical description of significant amount of experimental data possible and open the way for purposeful governing by oxide powder system on the stages of obtaining, compaction, and sintering. The investigations of zirconia nanopowders doped yttrium and chromium (ZrYCxy) [2] found unexpected result: the introduction of chromium oxide increases crystalline size comparing to reference sample (ZYC0.0) and with increasing chromium content particles begin to grow slower, reaching minimum value at maximum concentration of chromium (Figure 3). The Y/Zr, Cr/Zr and O/(Zr + Y + Cr) ratios were calculated from Zr 3d, Y 3d, Cr 2p and O 1s measured XPS spectra by dividing corresponding areas under the curve. The comparison with stoichiometric ratios clearly shows dramatic surface enrichment with yttrium for the ZYC0.1 sample. Other samples exhibit considerable yttrium depletion, which increase with the rise of chromium molar fracture. Four samples doped with chromium demonstrate significant enrichment with Cr atoms of the nanoparticles surface. Deconvolution of Cr 2p3/2 spectra shows Cr present in three states Cr(II) (575.5 eV), Cr(III) (576.5 eV) and Cr(III) (577.5 eV) Table 1. These states correspond to CrO, Cr2O3 and Cr(OH)3 respectively [4-6]. Ratio between oxide states of chromium is changing with chromium concentration increase. ZYC0.1 2+ 3+ sample include almost equal amounts of Cr and Cr states with 18% of chromium hydroxide states. Cr(II) amount is maximum for ZYC0.25 sample with reverse for Cr(III) and Cr3+(OH)3 states correlating with m-phase maximum. It is found the increase of m-phase value could be connected with lattice distortion due to presence of 2+ chromium atoms on the surface of nanopowders in Cr states. Results obtained for cromium doped zirconia nanopowders are important for using these material catalytic processes for formation nanoparticles of tipe “core-shell”, nanocomposites, etc.


Table 1 Components intensities for deconvolution of Cr 2p3/2 XPS spectra. 2+ 3+ Sample Cr , %, Eb=575.5 eV [4] Cr , %, Eb=576.5 eV [7] ZYC0.1 41.3 41.1 ZYC0.25 58.8 31.0 ZYC0.5 33.8 43.0 ZYC1.0 28.5 47.6

3+

Cr (OH)3 %, Eb=577.5 eV [5] 17.6 10.3 23.1 24.0

Acknowledgment This work is supported by the European Commission's Seventh Framework Programme (FP7), through the Marie Curie International Research Staff Exchange Scheme NANO_GUARD (PIRSES-GA-2010269138). References [1] [2] [3] [4] [5] [6] [7]

T.Konstantinova, I.Danilenko, V.Glazunova, G.Volkova and O. Gorban, J Nanopart Res, 13, (2011) 4015–4023 I.A. Yashchishyn, A.M. Korduban, T.E. Konstantinova, I.A. Danilenko, G.K. Volkova, V.A. Glazunova, V.O. Kandyba, Applied Surface Science, 256 (2010) 7175–7177 A.M. Korduban, I.A. Yashchishyn, T.E. Konstantinova, et al., Functional Materials 14 (2007) 454. A.B. Gaspar, C.A. Perez, L.C. Dieguez, 252, App. Surf. Sci. 939 (2005). C. Battistoni, J.L. Dormann, D. Fiorani, et al., Solid State Communic 39 (1981) 581. B. Stypula, J. Stoch, Corrosion Science 36 (1994) 2159. A. Galtayries, R. Sporken, J. Riga, et al., Journal of Electron Spectroscopy and Related Phenomena 88-91 (1998) 951.

Figures (a)

(b)

(c)

Figure 1. Morphology of nanopowders ZrO2+3 mol% Y2O3 calcined at different temperatures (a) -500ºC; (b) -700ºC; (c) -1,000ºC

Figure 2. Dependence of nanoparticle size (coherent scattering area (CSA)) via calcination temperature, calcination time 2 h

Figure 3. Crystalline size and phase composition vs. Cr2O3 concentration as determined by XRD analysis (line is drawn only to guide the eye).


Simple and Cost-Effective Synthesis of Carbon Nanodots and Their Application as Luminescent Probes

M.C. Ortega-Liébana1,2, José L. Hueso1,2, Raúl Arenal3,4, Jesús Santamaría1,2 1

Institute of Nanoscience of Aragon (INA) and Department of Chemical Engineering and Environmental Technology, University of Zaragoza, Zaragoza, Spain. 2 CIBER de Bioingeniería, Biomateriales y Nanomedicina, CIBER-BBN, 50018-Zaragoza 3 Advanced Microscopy Laboratory (LMA) and Institute of Nanoscience of Aragon (INA). 4 ARAID Foundation, Zaragoza, Spain. E-mail: jlhueso@unizar.es; Jesus.Santamaria@unizar.es

Abstract Research on photoluminescent compounds have experienced a fast development in the last decades, due to their promising and diverse applications ranging from optoelectronics to biology, especially in the rapidly growing field on bionanotechnology [1]. Carbon nanodots (C-dots), as a new type of fluorescent nanomaterial have shown superior properties compared with conventional organic dyes and high-cost fluorophores [2-3]. Carbon-based nanodots may offer substantial advantages such as: (i) lower toxicity in comparison to other semiconductor quantum dots; (ii) high stability and limited blinking effects; (iii) abundance and low-cost production; (iv) wide emission spectrum within the UV-Visible range; (v) flexible surface chemistry to attach biomedical markers. In the present work, we report a simple and cost-effective approach for the preparation of carbon nanoparticles under hydrothermal conditions with excellent luminescent properties in a wide spectrum range. We have evaluated different parameters such as reaction time, temperature of synthesis, organic compounds used as carbon sources and other co-reactants as additives. Several characterization techniques such as TEM, FT-IR, XPS and UV-Vis spectroscopy have shown the production of carbon nanoparticles with different size and emission ranges from UV to green with high quantum yields and long-term stability (see Figure 1-A for a representative example). We have evaluated the influence of pH on the luminescence properties of these C-dots. The results show a clear influence on the final PL emission wavelengths and their relative luminescence intensities (Figure 1B). The maximum fluorescence activity of the C-dots was observed within the range of pH 4-9. Nevertheless, the presence of highly alkaline media partially quenches the overall PL intensity and favors a progressive shift of the emission wavelengths (Figure 1C). This optical behavior is tunable and reversible upon pH variations, thereby providing the C-Dots with a potential capacity as pH-nanosensor (Figure 1C). Moreover, the enhanced luminescent exhibited at physiological pH values makes them good candidates for biological labeling and imaging applications. Further investigations have also shown the potential application of these C-Dots as selective nanosensors of metal ions [4-5]. It is especially remarkable the high selectivity shown in the presence of 2+ Cu cations. The PL emission is progressively quenched even in the presence of ppb amounts. The selectivity detection limit in the presence of additional metal ions remains stable and reproducible in the micromolar range (ppm) (Figure 1D). These preliminary results suggest that sensor platforms based on C-dot can in principle respond to complex environments, serving as probes for the detection of analytically important metals of vital importance for biological monitoring and wastewater management. References [1] Z. Kang, Y. Liu, S. Lee et al. J. Mater. Chem. 22 (2012) 24175-24175. [2] S.N. Baker and G.A. Baker, Angew. Chem. Int. Ed. 49 (2010) 6726. [3] M.J. Krysmann, A. Kelarakis, P. Dallas, E.P. Giannelis, J. Am. Chem. Soc. 134 (2012) 747. [4] Y. Liu, C.Y. Liu, Z.Y. Zhang. Applied Surface Science. 263 (2012) 481. [5] A. Salinas-Castillo,M. Ariza-Avidad, C. Pritz, M. Camprubi-Robles, B. Fernandez,M.J Ruedas-Rama, A. Megia-Fernandez, A. Lapresta-Fernandez, F. Santoyo-Gonzalez, A. Schrott-Fischer, L.F. CapitanVallvey. Chemical Communications, 49 (2013) 1103.


Figures

Figure 1. (A) Representative TEM image of carbon nanodots obtained by hydrothermal synthesis; (B) Photoluminescence emission spectra at different pH values (位exc = 450 nm); (C) Photoluminescence emission intensities evolution upon the variation of pH conditions; (D) Photoluminescence quenching effect induced by increasing concentrations of copper ions; Inset: digital photograph of a colloidal solution containing C-dots and excited under an UV lamp (位exc= 400 nm).


Development of carbon nanotubes/polypropylene nanocomposites with ESD and fire retardancy properties for and innovative sandwich panel Amaya Ortega, Olivia Menes, Adolfo Benedito, Sergio Fita, BegoĂąa Galindo, Neus Soriano AIMPLAS,Instituto TecnolĂłgico del PlĂĄstico Gustave Eiffel, 4. 46980. Paterna, Valencia (Spain) aortega@aimplas.es Abstract (Arial 10) Composite sandwich panels are versatile materials used in lightweight structures for building sector. Different properties are required in the final application such as a high strength, flexural rigidity and a suitable insulation. Other important technological qualities to take into account in this field are the electrostatic discharge (ESD) and fire retardancy. In several building areas, where is possible to find electronic equipments or similar devices, it is important to discharge the electrostatic charge to avoid sparks or failures in systems1 and to protect the surface against flame. In this regard, carbon nanostructures are a suitable candidate to achieve these requirements2 due to their intrinsically electrical properties3,4. Moreover, combined with other nanostructured materials, fire performance properties can also be improved. In the present study, an innovative polypropylene nanocomposite sheets have been developed via onestep extrusion process combining synergistic effects of different nanoparticles. Rheological and optical microscopy results showed an optimal dispersion of nanofiller in polymer matrix. Furthermore, mechanical properties have been enhanced by means of this development. Finally, antistatic and fire retardancy properties were achieved at low content of well dispersed carbon nanotubes combining with an intumescent nanomaterial coating.

This research was supported by Territorial Cooperation Program INTERREG IVB SUDOE project CarbonInspired (SOE2/P1/E281) co-funded with FEDER fund.

References [1] J. M. Kolyer, D.E. Watson. Chapman and Hall, (1999). [2] S. Jain, P. Kang, Y. Heung. Smart structures and materials (2004). [3] Z. Spitalsky, D. Tasis, K. Papagelis, C. Galiotis. Progress in Polymer Science, 35 (2010) 357-401. [4] S.Kumar, B. Lively, L.L. Sun, B.Li, W.H. Zhong. Carbon, 48 (2010) 3846-3857.


Figures

Figure 1. Rheological oscillatory analysis of neat polypropylene and nanocarbon composites.

Figure 2. Flammability test for sandwich panels.


Periodic Nanohole Arrays for Localized Surface Plasmon Resonance Label-Free Biosensing by Thermal Nanoimprint Lithography 1,2

2

1,2

1,2

D. Otaduy , J. Martínez-Perdiguero , A. Retolaza , A. Juarros , R. Diez-Ahedo 1 2

1,2

1,2

and S. Merino .

IK4-Tekniker, Micro and Nano Fabrication Unit, C/ Iñaki Goenaga 5, Eibar 20600, Spain.

CIC microGUNE, Goiru Kalea 9 Polo Innovación Garaia, 20500 Arrasate-Mondragón, Spain. dotaduy@cicmicrogune.es

Abstract Surface plasmon resonance (SPR) sensors are a common tool for real-time label-free biosensing because of their ease of use and good performance. The Kretschmann configuration [1] is the most used commercial SPR systems requiring a somehow complex non-collinear optical set-up. The use of enhanced transmission through metallic sub-wavelength nanohole arrays [2] to couple the incoming light to surface polaritons has proven to be a very good alternative because of its simple linear set-up and boasts higher spatial resolution [4], making it feasible for the miniaturization of the sensing device. Ordered nanoholes arrays are usually fabricated by Focused Ion Beam (FIB) [2] [3], or Electron Beam Lithography (EBL) [4]. However, although these techniques have very high resolution, the fabrication of arrays require long processing times, that means, low throughput and the associated high cost and therefore, they are not suitable for mass-production. Nanoimprint Lithography (NIL) is high throughput, low-cost, and high fidelity pattern transfer technique which allows obtaining nanometer scale features on large size wafers [5], having a great potential to be scaled up to real production. Here, we report on the fabrication of periodic gold nanohole arrays on glass substrates using thermal NIL process on a single resist layer, with 400nm and 500nm periodicities and hole diameters of ranging from 150 to 200nm (figure 1). The footprints of the arrays vary from 20µm up to 600µm, proving the feasibility of imprinting over large areas. The fabrication process was optimized and the arrays were fully characterized. It has been proved to be repetitive and the quality of the arrays similar to those manufactured using FIB or ELB. The extraordinary optical transmission through the nanohole arrays was measured in a designed optical set-up and the sensitivity, 126nm/RIU, was calculated using solutions of known refractive index (n), figure 2. Moreover, the biosensing capabilities of the fabricated arrays have been demonstrated monitoring in real-time the absorption of bovine serum albumina (BSA) protein onto the gold surface without the necessity of labels. In figure 3 it can be seen that the injection of BSA protein at t=120s results in a change of the transmitted spectra which can be measured as an intensity change at a given wavelength and at t≈800s the gold surface was saturated with BSA and no further absorption took place. References [1]

E. C. Nice and B. Catimel, “Instrumental biosensors: new perspectives for the analysis of biomolecular interactions” BioEssays. vol. 21, no. 4, Apr. (1999), pp. 339–52. [2] T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature, vol. 391, Feb. (1998), pp. 667–669. [3] A. Lesuffleur, H. Im, N. C. Lindquist, and S.-H. Oh, “Periodic nanohole arrays with shape-enhanced plasmon resonance as real-time biosensors,” Applied Physics Letters, vol. 90, no. 24, (2007), p. 243110. [4] J. C. Sharpe, J. S. Mitchell, L. Lin, N. Sedoglavich, and R. J. Blaikie, “Gold nanohole array substrates as immunobiosensors.,” Analytical chemistry, vol. 80, no. 6, (2008), pp. 2244–9. [5] S. Y. Chou, et al., “Nanoimprint lithography,” vol. 14, no. June, (1996), pp. 4129–4133.


Figures

Figure 2: SEM image of a gold nanohole array fabricated by NIL (hole diameter 155nm, periodicity 500 nm)

a)

b)

Figure 2: a) Transmission spectra through four sucrose solutions at different concentrations. A clear red shift with increasing concentration (or n value) can be observed; b) Wavelength shift vs. solution refractive index, linear change of the peak can be observed. From the linear regression, 126 nm/RIU sensitivity was obtained.

a)

b)

Figure 3: a) Transmission spectra through a gold nanohole array in contact with PBS buffer (crosses) and after 1 hour incubation of a solution of 50 g/ml BSA solution in PBS buffer (circles) b) Real-time label-free monitoring of the BSA adsorption to the gold surface. The injection of BSA protein at t=150 results in a change of the transmitted spectra which can be measured as an intensity change at a given wavelength. In this case =645nm was chosen because it gave the maximum change (see vertical line in (a)). It can be observed that at after 800s the surface was saturated with BSA and no further adsorption took place.


Angle-dependent magnetoresistance measurements of individual GaAs/(Ga,Mn)As core-shell nanowires at low temperature and high magnetic fields with in-situ double rotator 1

2

2

F. Otto , C. H. Butschkow , D. Weiss 1

2

attocube systems AG, Koeniginstr. 11a, 80539 Munich, Germany Inst. for Exp. and Appl. Physics, University of Regensburg, Universitaetsstr. 31, 93053 Regensburg, Germany florian.otto@attocube.com

Many interesting quantum phenomena require the relative rotation of a strong magnetic field at low (or even ultra-low) temperature with respect to a mesoscopic sample, be it semiconductors / nanomagnets with magnetic anistropies or superconductors with anisotropic gap structures. While readily available, commercial vector magnets (2D/3D) are usually significantly more expensive than single solenoids, despite delivering much smaller fields due to the limitations set by split coil magnets. Instead of rotating the field vector, the atto3DR - attocube's 3-dimensional rotator module - provides access to the full magnetic field (e.g. 9 T) in all directions relative to the sample surface, by rotating the sample in-situ. We discuss the key features of the setup, and show first measurement results at both 4 K: Magnetoresistance measurements on individual GaAs/(Ga,Mn)As core-shell nanowires have been conducted (similar to [2], see figure 1). The uniaxial magnetic anisotropy of a nanowire can be examined by performing measurements for different rotation planes. However, due to the random distribution of the nanowires on the substrate, the implementation of such an experiment is in general not straight forward. Using the convenience of a double rotator as the atto3DR, this is easily realizable in this setup (see figure 2). The module [3] consists of two piezo based ‘slip-stick’ rotators (with resistive encoders for full closed loop operation), which allow for arbitrary orientations of an external magnetic field vector and the sample plane. In addition, it features 20 measurement lines fully wired and a convenient leadless ceramic chip carrier (LCCC) mount for easy sample exchange. References

[1] A. Rudolph, M. Soda, M. Kiessling, T. Wojtowicz, D. Schuh, W. Wegscheider, J. Zweck, C. Back, and E. Reiger, Nano Lett. 9, 3860–6 (2009).

[2] C. H. Butschkow, E. Reiger, S. Geißler, A. Rudolph, M. Soda, D. Schuh, G. Woltersdorf, W. Wegscheider, and D. Weiss, arXiv:1110.5507 (2011).

[3] www.attocube.com/attoCRYO/atto3DR.html Figures


Figure 1: Normalized magnetoresistance as a function of the angle between externally applied magnetic field and the nanowire axis for various magnitudes of the external magnetic field. Inset (top left): Tilted scanning electron micrograph of a contacted nanowire. Black arrows indicate the sample coordinate system. Coloured arrows indicate the different rotational directions as used in the measurements (blue: transverse, orange: in-plane, green:perpendicular rotation).

Figure 2: Working principle of the double rotator module and possible relative orientations between external magnetic field vector and sample surface.


Steady-state and Transient Measurements of 0.8-2.0 m Luminescence of PbS Quantum Dots P. S. Parfenov, A. P. Litvin, A. V. Baranov, E. V. Ushakova, A. O. Orlova, A. V. Fedorov Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, Kronverkskiy pr., 49, Saint Petersburg, Russia qrspeter@pochta.ru Abstract We describe a new experimental setup developed for luminescence measurements in the near-infrared region. The setup let us obtain spectral and time-resolved parameters of nanostructure’s luminescence in spectral range 0.8–2 μm for stationary analysis with spectral resolution of 7 nm and 0.8–1.7 μm for time-resolved luminescence measurements with time resolution of 2 ns. We discuss technical parameters of the setup and demonstrate its capabilities on the example of PbS quantum dots (QDs) luminescence measurements. Spectral luminescence analysis and luminescence decay measurements are important for understanding of charge carrier dynamics, energy levels structure and processes of energy relaxation in semiconductor QDs [1]. However there is a lack of sensitive commercial equipment for such experiments. Because our setup is mainly intended for PbS QDs luminescence analysis, we took into account some features of this objects’ luminescence: wide spectral range, long decay times and difficulties with signal receiving as consequence. At the same time powerful sources of excitation radiation should not be used to avoid a photobleaching and multiple electron-hole pair generation. We use conventional 90 degree detection geometry (fig. 1). The setup consists of continuous and pulsed lasers, monochromators, InGaAs photodiodes, amplifiers, an oscilloscope, and auxiliary optical elements. For stationary measurements 532 nm and 633 nm continuous lasers, an Acton monochromator, cooled Hamamatsu InGaAs photodiodes, and self-made FET preamplifier are used [2]. Spectral sensitivity has been calibrated using a black body source [3]. In time-resolved mode a 635 nm and 980 nm PiqoQuant pulsed lasers are used. Collected radiation is sent through the self-made monochromator or bandpass filters and focused on Femto high-speed InGaAs photoreceiver with buildin preamplifier. The received signal is additionally amplified by Stanford Research amplifier and then registered by PiqoScope hi-speed PC oscilloscope [4]. A purpose-built computer program accumulates 5 the results of measurement to get reliable signal/noise ratio. Signal acquisition rate is above 10 waveforms per minute, therefore up to tens of millions waveforms can be accumulated. The setup capabilities and features are demonstrated on PbS QDs luminescence. The setup lets us to carry out spectral measurements in a wide range of QDs sizes (2.7–7.6 nm) and establish size dependencies of its optical properties [1]. Luminescence lifetimes can be measured in the time range 20 ns – 10 μs that makes us able to obtain luminescence decay curves for PbS QDs in solutions and embedded into the porous matrix. Acknowledgement The authors thank financial support from the RFBR (Grants 12-02-01263 and 12-02-00938) and the Ministry of Education and Science of the Russian Federation (Projects 11.519.11.3020, 11.519.11.3026, № 14.B37.21.0741 and 14.В37.21.1954).

References [1] Ushakova E.V., Litvin A.P., Parfenov P., Fedorov A.V., Artemyev M., Prudnikau A.V., Rukhlenko I.D., Baranov A.V., ACS Nano, 10 (2012) 8913. [2] Parfenov P.S., Baranov A.V., Veniaminov A.V., Orlova A.O. Journal of Optical Technology, 2 (2011) 120. [3] Parfenov P.S., Litvin A.P., Baranov A.V., Veniaminov A.V., Ushakova E.V., Journal of Applied Spectroscopy, 3 (2011) 433. [4] Parfenov P., Litvin A.P., Baranov A.V., Ushakova E.V., Fedorov A.V., Prudnikov A.V., Artemyev M.V., Optics and Spectroscopy, 6 (2012) 868.


Figures

Fig. 1 Functional diagram of the setup for PbS QDs luminescence analysis: (L532, L633) 532 and 633 nm continuous lasers; (L635, L980) 635 and 980 nm PicoQuant pulsed lasers; (FM1,FM2) flipping mirrors; (M) a mirror; (L1â&#x20AC;&#x201C;L7) lenses; (C) a cuvette or a sample holder; (OF) an optical fiber; (F) an optical filter; (M1) Acton SP-2558 monochromator; (M2) a compact monochromator with f/3 aperture; (PD) Hamamatsu G5852-21 or G8605-21 photodiodes; (CPS) a cooler power supply; (TIA) a transimpedance amplifier; (SH) Acton SpectraHub; (HSPD) Femto HCA-S-200M-IN hi-speed photodiode; (AMP) Stanford Research SR445A amplifier; (OSC) PicoScope 3206A oscilloscope, (GEN) a frequency generator; (CU) PicoQuant PDL-800B laser control unit; and (PC) a computer.


Biosilica nanostructures synthesis and simultaneous CdTe quantum dots immobilization Marieta L. C. Passos, Mariana Pereira, M. Lúcia M. F. S. Saraiva, João L. M. Santos and Christian Frigerio REQUIMTE, Department of Chemistry, Faculty of Pharmacy, University of Porto, Rua Jorge Viterbo Ferreira, 228 Ed. 3, Piso 2, 4050-313 Porto, Portugal. marietapassos@gmail.com Abstract In the nature, diatoms and sponges are able to take up silicon from the environment in soluble form as silicic acid, store it in the cell and catalyze its polymerization into silica with precise structure architecture down to nanoscale [1, 2]. This production of nanostructured silica in natural systems has been considered a process to mimic [3]. The interest in the biomimetic synthesis of silica-based materials is increasing, and in the last few years these phenomena has been an inspiration for the development of novel fabrication procedures in nanobiotechnology [4]. The mimetization of these natural phenomena minimizes the long reaction times and the multiple steps of complex protocols [2, 5]. Moreover, it avoids the use of harsh and environmentally unfriendly conditions such as toxic and expensive organic solvents, high temperature and pressure and high or low pH. The processing of nanostructure particles in water under mild conditions, by using either synthetic or biologically-derived amine-containing macromolecules as additives, mediators or templates characterizes the biomimetic synthesis. The ability to manipulate all these conditions enables the controlling of the morphology of silica materials with a high level of precision and provides a powerful paradigm for the construction of biological nanostructures, involving other nanoparticles, such as quantum dots, with wide potential applications in the catalysis, diagnostic, therapeutic and biomedical fields. Colloidal semiconductor nanocrystals or quantum dots (QDs) are monodisperse crystalline clusters of atoms with size normally comprised between 1 and 10 nm and with peculiars characteristics due to their low dimension [6]. In this work, CdTe quantum dots were synthesized, by wet chemistry using mercaptopropionic acid (MPA) as stabilizing agent by Zou’s method [7] with some modifications. Then QDs were encapsulated during the biosilica synthesis, a very rapid process (in seconds). Different parameters that could influence the biosilica particle synthesis and the QD immobilization were evaluated. It was observed that some experimental conditions as silica precursors, catalysts, pH and anions concentrations influence the encapsulation efficiency and the size and the shape of biosilica nanoparticles (Figure 1). Moreover, it was also tested the stability and fluorescent character of quantum dots encapsulated in silica matrix (Figure 2).

References [1] Hildebrand, M., Chem. Rev., 108 (2008) 4855. [2] Jin, R. and Yuan, J. Learning from biosilica: nanostructured silicas and their coatings on substracts by programmable approaches. In Advances in biomimetics. Edited by George A. InTech, (2011), Rijeka. [3] Sumper, M., Brunner, E., Adv. Funct. Mater., 16 (2006) 17. [4] Schroder, H. C.,Wang, X. H., Tremel, W.,Ushijima, H., and Muller, W. E. G, Nat. Prod. Rep., 25 (2008) 455. [5] Yang, H.,Coombs, N. and Ozin, G. A., Nature, 386 (1997) 692. [6] Rogach, A. L., Semiconductor Nanocrystal Quantum Dots, (2008), Verlag, Wien. [7] Zou, L., Gu, Z., Zhang, N., Fang, Y. Z., Zhu, W. and Zhong, X. J., J. Mater. Chem., 18 (2008) 2807.


Figures

Figure 1 - Scan electron microscopy (SEM) images of synthesized QDs biosilica nanoparticles with different buffer conditions.

Figure 2 - Fluorescence microscopy image of biosilica with immobilized CdTe-MPA quantum dots.


Exploring thermally-induced states in square artificial spin-ice arrays (1)

(1)

(1)

J.M. Porro , A. Bedoya-Pinto , A. Berger , P. Vavassori

(1)(2)

(1) CIC nanoGUNE Consolider, Tolosa Hiribidea 76, E-20018, Donostia-San Sebastián (2) Ikerbasque, Basque Science Foundation, E-48011, Bilbao t.porro@nanogune.eu

Intrinsic frustration phenomena are widely found in natural systems, as it is the case of water ice with the existing frustration on the hydrogen and oxygen atoms [1]. Another example of naturally occurring frustration is observed in rare-earth alloys, where magnetic frustration is present among the magnetic moments of the rare earth ions due to the crystal geometry of the material. For this reason, these systems are called ‘spin-ice’ systems [2]. Spin-ice physics can be conveniently studied by means of the so-called artificial spin-ice systems, which are arrays of magnetic nanoislands fabricated in different geometries inducing the spin-ice frustration in a 2D system [3,4]. We present a methodology to explore experimentally the formation of thermally-induced long range ground-state ordering in artificial spin-ice systems [5]. Our novel approach is based on the thermalization of a square artificial spin-ice array of elongated ferromagnetic nanoislands made of a FeNi alloy characterized by a Curie temperature about 100K lower than that of Permalloy (Ni81Fe19), which is commonly used for this kind of investigations. The drop of M(T) when the sample is heated close to its Curie temperature, reduces the shape anisotropy barrier of each island and allows us to bring the artificial spin-ice pattern above the blocking temperature of the islands, thus “melting” the spin-ice system, without damaging the sample. The magnetization configuration resulting by the thermal excitation of the islands and the frustrated dipolar interactions among them, can be then imaged by magnetic force microscopy or any other kind of magnetic microscopy imaging after cooling down the sample back to room temperature. The nanomagnets have dimensions of 300x100x25nm, with a lattice parameter of 380nm. We obtained thermal demagnetized states similar to the as-grown magnetization states obtained in [4], and compared them to the demagnetized configurations obtained applying a sample-rotating in-plane magnetic field demagnetization protocol [6] by using Magnetic Force Microscopy, as can be observed in Fig.1. After applying an in-plane rotating field demagnetization protocol to our artificial spin-ice pattern, we obtain short-range ground state spin-ice ordering. Nevertheless, when applying our thermal demagnetization protocol we find long-range ground state spin-ice ordering with a substantial energy reduction of the remanent magnetization state in a repeatable fashion. References [1] S.T. Bramwell and M.J.P. Gingras, Science 294, 1495 (2001) [2] M.J. Harris et al., Phys.Rev.Lett. 79, 2554 (1997) [3] R.F. Wang et al., Nature 439, 303 (2006) [4] J.P. Morgan et al., Nature Physics 7, 75 (2011) [5] J.M. Porro et al., New J. Phys., submitted dec.2012. [6] R.F. Wang et al., J.Appl.Phys. 101, 09J104 (2007)


Figures

Fig.1: magnetization states after applying a sample-rotating in-plane magnetic field demagnetization protocol (left) and after melting the artificial spin-ice pattern over its blocking temperature (right), and a graphic of the vertex type populations (1-less energetic, 4-most energetic) obtained with the field demagnetization protocol (blue) and the thermal demagnetization protocol (red).


Conjugates of bile acid platinum complexes with gold nanoparticles a

b

b

Emilio Rodríguez-Fernández , Ángel Alonso-Mateos , Mª Jesús Almendral-Parra , Julio J Criadoa c a c b Talavera , Manuel Fuentes , Juan Luis Manzano-Íscar , Alberto Orfao , Sara Sánchez-Paradinas a

b

Departamento de Química Inorgánica; Departamento de Química Analítica, Facultad de Ciencias c Químicas Universidad de Salamanca, 37008-Salamanca, Spain. Centro de Investigación del Cáncer (CIC; IBMCC CSIC/USAL) Servicio de Citometría, Departamento de Medicina and IBSAL, Universidad de Salamanca 37007 Salamanca, Spain. erodri@usal.es

Abstract The bisursodeoxycholate(ethylenediamine)platinum(II), [Pt(UDC)2(en)], synthesized according to the procedure of Criado et al.[1-3]

PtU2

compound

was

The conjugates of PtU2 with gold nanoparticles (PtU2-AuNP) were prepared by mixing the solid PtU2 compound directly in the colloidal solution of the nanoparticles. All the solutions were vortexed for at least twenty minutes and then stored at 4°C until use in cell cultures. The conjugates were characterized by UV-visible spectroscopy, fluorescence emission spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) (Figures 1 and 2). The PtU2-AuNP complex exerted an important cytotoxic activity against MG63 osteosarcoma cells which was already clearly detectable after 48 h of culture (Figure 3) [4]. The precise mechanisms by which the presence of AuNPs increases the cytotoxic activity of the drug remain elusive and require further investigations. References [1] M. Pérez-Andrés, J. J. Benito, E. Rodríguez-Fernández, B. Corradetti, D. Primo, J. L. Manzano, Alberto Orfao and Julio J. Criado. Dalton Trans. (2008) 6159-6164. [2] Criado, J J; Rodríguez, E; Manzano J L; Alonso, A; Barrena, S; Medarde, M; Pelaez, R; Tabernero, M D; Orfao, A. Bioconjugate Chem. 16 (2005) 275-282. [3] Pérez-Andrés, M.; Benito, J. J.; Rodríguez-Fernández, E.; Manzano, J. L.; Barrena, S.; Orfao, A.; Criado, J. J. Letters in Drug Desing and Discovery, 4 (2007) 341-345. [4] Pending of publication. Acknowledgment This work has been supported by a grant from the Foundation “Samuel Solórzano Barruso (2013)”


Figures Figure 1. Fluorescence of PtU2 and it adduct with AuNp. 11 AuNp20 (c = 7路10 Np/mL) (Au) -4 PtU2 (c = 4,5路10 M) (Pt) Adduct 1:1 (Au+Pt)

100

Fluorescence (a. u.)

80 60 40

Au+Pt

20

Pt Au

0 250 300 350 400 450 500 550 600 650 位 (nm) 1

21

A

18 19 13

HO O

HUDC

12

20

24

10 16

7

1 5

OH

2 3

OH

i) ii)

Figure 2. (A) H-NMR spectra of the platinum compound (i) and its incubation adduct with gold nanoparticles (ii). HUDC = ursodeoxycholic acid. TEM (B) and SEM (C) images of the PtU2-AuNPs conjugate drug complex in water. After adducts formation, the 1 corresponding H-NMR signals (methyl groups C18, C19 and C21), slightly shifted to 0.55 ppm, 0.79 ppm and 0.85 ppm, respectively.

C

B

50 nm

2 渭M

Figure 3 Cytotoxic activity of the PtU2 compound (straight line) and the newly-synthesized PtU2-AuNP complex (curved line) against MG63 (osteosarcoma) cells. Cytotoxic activity against MG63 osteosarcoma cells which was already clearly detectable after 48 h of culture. Cytotoxic activity is specific for the PtU2AuNPs complex, since no cytotoxic activity was detected when the cells were incubated with the AuNPs alone.


Wave packet dynamics in graphene nanostructures E. Romera1, N. A. Cordero2, T. García1 , I. G. Ayala2, and F. de los Santos3 1

Departamento de Física Atómica, Molecular y Nuclear, Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Campus Fuentenueva E-18071 Granada, Spain. 2 Departamento de Física, Universidad de Burgos. Spain. 3 Departamento de Física Atómica, Molecular y Nuclear, Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Campus Fuentenueva E-18071 Granada, Spain. eromera@ugr.es Abstract We have studied the existence of quantum revivals in graphene quantum nanostructures within a theoretical framework. The time evolution of a Gaussianly populated wave packet show revivals in monolayer and bilayer graphene structures (quantum dots and quantum rings). We have also studied this behavior for these nanostructures in magnetic fiels. References [1] E. Romera, F. de los Santos, Phys. Rev. B 80 (2009) 165416. [2] E. Romera and J. J. Torres, Phys. Rev. B 82 (2010) 155419. [3] E. Romera and J. J. Torres, AIP advances 2 (2012) 042121. [4] T. García, S. Rodríguez-Bolivar, N. Cordero and E. Romera, Preprint. 2013.


ONE-DIMENSIONAL METAL-AMINOACID AND METAL-PEPTIDE NANOSTRUCTURES AND THEIR USE AS TEMPLATES FOR INORGANIC NANOPARTICLE SUPERSTRUCTURE SYNTHESIS Marta Rubio-Martínez1, Josep Puigmartí-Luis2, Inhar Imaz1,Daniel Maspoch1,3 1

CIN2 (ICN-CSIC), Catalan Institute of Nanotechnology, Esfera UAB, 08193 Bellaterra, Spain. 2Institut

de Ciència de Materials (ICMAB-CSIC), Esfera UAB, 08193 Bellaterra, Spain. ³Institució Catalana de Recerca i Estudis Avançats (ICREA), 08100 Barcelona, Spain marta.rubio@icn.cat, daniel.maspoch@icn.cat

Extended metal-organic networks built up from the combination of organic and inorganic building blocks are among the most attractive materials today. Because of their vast compositional and structural versatility, these materials show promise for a myriad of applications, such as gas sorption, storage, catalysis, separation and magnetism. At the nanoscale, these materials can show sizedependent properties which, if properly exploited, may expand the scope of these materials in numerous practical applications, including drug-delivery, contrast agents, sensor technology, scaffolds, electronics, functional membranes and thin-films. Many potential applications of these metal-organic materials may require them to be constructed from benign building blocks that are biologically and environmentally compatible. Recently, biomolecules have

emerged

as

building

blocks

for

constructing

extended

metal-biomolecule

net

1

works. Biomolecules such as aminoacids and peptides offer several advantages as organic building blocks because they are readily and naturally available in quantities and at prices amenable to preparing bulk quantities of materials; they can lead to biologically-compatible materials; they are structurally diverse; they can have many different metal-binding sites, and consequently, they can exhibit multiple possible coordination modes, a feature that increases the potential structural diversity of these materials; they

have intrinsic self-assembly properties which can be used to direct the

structure and function of the resulting materials; and they are chiral. In this communication, we will show our latest advances in the development of new synthetic methodologies that enable the self-assembly of metal ions and aminoacids and peptides into onedimensional (1-D) nanostructures.2,3These novel methods include fast precipitation, diffusion and specially microfluidic technologies. The resulting nanofibers, nanowires and nanobelts made of aminoacids (e.g. aspartic acid and cysteine) and peptides incorporate the intrinsic characteristics of these biomolecules, such as their selective recognition and chirality. Furthermore, because of the recognition capacities, we will show how these metal-biomolecule nanostructures can be used as dual biotemplates to form sophisticated self-assembled inorganic nanoparticle superstructures, such as bimetallic 1-D superstructures made of Fe3O4 and Ag nanoparticles that marry the magnetic and conductive properties of the two nanoparticle types.


Figure 1. (Left) Schematic illustration of the formation of metal-aminoacid nanofibers using microfluidics. (Right) Representative SEM image ofCu(II)-aspartic acid nanofibers.

1.I. Imaz, M. Rubio-Martínez, J.An, I. Solé-Font, N. L. Rosi, D. Maspoch, Chem. Commun.2011, 47, 7287. 2. I.Imaz, M. Rubio-Martínez, W. J. Saletra, D. Amabilino, D. Maspoch, J. Am. Chem. Soc. 2009, 131, 18222 3. J. Puigmartí-Luis, M. Rubio-Martínez, U. Hartfelder, I. Imaz, D. Maspoch, P. S. Dittrich, J. Am. Chem. Soc. 2011, 133, 4216.


Study of carbon encapsulated iron nanoparticles produced by a modified arc discharge by applying nitrogen, argon and helium M. Reza Sanaee, S. Chaitoglou, V.-M. Freire, N. Aguiló-Aguayo, E. Bertran FEMAN Group, Institute of Nanoscience and Nanotechnology (IN2UB), Dep. Applied Physics and Optics, Universitat de Barcelona, Martí Franquès, 1, E08028 Barcelona, Spain sanaee@ub.edu The influences of nitrogen, argon, and helium on the particle size, composition, crystallinity, and the magnetic properties of carbon encapsulated iron nanoparticles (CEINPs) produced at near-atmospheric pressure conditions (5–8·104 Pa) were studied in this project. Core size and shell thickness have a direct effect on magnetic properties and on oxidation prevention of iron core, respectively. The observations by TEM and SEM revealed a straight relation between the nature of the inert gas and the sizes of both iron core and carbon shell. Energy-dispersive X-ray analysis (EDX) and electron energy loss spectroscopy (EELS) provided composition and elemental mapping of CEINPs. Raman Spectroscopy was used to study the degree of carbon order-disorder. Influences of nitrogen and argon on the plasma region evidenced higher evaporation of carbon content comparing to helium plasma. Consequently, large spherical carbon shell of 220 nm, 188 nm, and 41 nm encapsulate iron cores when nitrogen, argon and helium have been used, respectively (Figure 1). Ultra small iron core were synthesized by using nitrogen (2.5 nm) and argon (3.4 nm), while three fold bigger iron cores (7.7 nm) obtained when helium plasma was used (Figure 2). Argon provides important effects on the structure of Fe@C nanoparticles [1]. Applying only argon demonstrates most size monodispersion and spherical shape of iron core (Fe core size: 3.4 ± 0.7 nm). Based on the Raman Spectroscopy results, best carbon crystallinity is observed when argon has been used and followed by applying nitrogen and helium. All the particles show a superparamagnetic behavior at temperatures above 225 K as determined by SQUID measurements (Figure 3) which opens the possibility of room temperature applications. The lower blocking temperature of samples with smaller iron core has been observed in line with TEM observations. Moreover, magnetic diameters using nitrogen, argon and helium (2-7 nm range) were similar to the core diameters observed by TEM. EELS and EDX analysis showed no trace of oxygen in iron cores, hence samples were well protected by carbon shells. It has been reported that a particle size range of 50–300 nm is strictly demanded and desired due to the diameter limitation of capillary walls [2]. Moreover, an optimum geometry for endocytotic uptake is 50 nm and spherical shape [3,4]. Our particles fulfilled the requirements of drug delivery applications in terms of size and shape. In addition, carbon shells are biocompatible and thermally stable, and they can be functionalized to receive suitable organic radicals. It is also concluded that the gas nature of the arc discharge reactor used in the research project has significant effect on the morphological properties of CEINPs. Accordingly, CEINPs can be synthetized based on the desired applications in biomedicine such as drug delivery, imaging and hyperthermia.

References [1] M. Reza Sanaee, S. Chaitoglou, N. Aguiló-Aguayo and E. Bertran, Oral peresentation in 9th International Conference on Nanosciences & Nanotechnologies held in Thessaloniki Greece, Influences of argon-helium mixtures on the carbon-coated iron nanoparticles produced by a modified arc discharge, 3-6 July (2012). [2] H. Cao, G. Huang, S. Xuan, Q. Wu, F. Gu and C. Li, Journal of Alloys and Compounds, Synthesis and characterization of carbon-coated iron core/shell nanostructures (2008) 272-276. [3] P. Decuzzi, R. Pasqualini, W. Arap and F. Mauro, Pharmaceutical Research, Intravascular Delivery of Particulate Systems: Does Geometry Really Matter? (2009) 235-243. [4] W. Jiang, B. Y. Kim, J. T. Rutka and W. C. W. Chan, Nature, Nanoparticle-mediated cellular response is size-dependent (2008) 145-150.


Figure 1. SEM image of spherical CEINPs

A B Figure 2. A: TEM overview of CEINPs, B: HTEM image of iron at carbon shell

A B Figure 3. A: Hysteresis loop of CEINPs at room temperature, B: Zero-field-cooled and field-cooled magnetization curves


Dynamics of Bloch oscillating transistor near divergence and its applicability for common mode signal rejection 1

1

2

Jayanta Sarkar , Antti Puska , Juha Hassel and Pertti J.Hakonen

1

1

Low Temperature Laboratory, O.V.Lounasamaa Laboratory, Aalto University, P.O. Box 13500, FI-00076 AALTO, Finland 2 VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Finland jay@boojum.hut.fi

Abstract: Bloch oscillating transistor is a combination of a Josephson junction or a squid connected with a large resistor and a NIS junction (c.f. Fig. 1). BOT was demonstrated as a 1 current amplifier which has a very low input equivalent noise of ~ 1fA/√Hz . The tendency of BOT 2 to bifurcate has been theoretically predicted and followed by experimental verification . We have 3 studied the dynamics of BOT near the bifurcation threshold . This is an important feature for an amplifier as this can be utilized to improve the performance characteristics of it. In this present work we have investigated it in more detail followed by a separate experiment with a differential pair BOT to determine the common mode rejection capability of this amplifier for the first time. Near the bifurcation point BOT behavior is fully governed by switching dynamics with the rates imposed by the biasing conditions. Near the bifurcation point the base current is a combination of a working point current not inducing inter-band transition, and a part that leads to transitions. The ratio of these two is given by <Ne>, which is the average number of tunneling events before a downward transition triggered by injected base current. We have measured the I-V characteristics of the BOT with different base currents (IB) over a wide range of Josephson coupling energy (EJ). A typical I-V with different IB is shown in Fig. 2. The current gain (β) is found to be increasing with increasing IB and eventually it diverges. We have found a record large β ~ 50 in our experiment. The base current, IB-H required for the onset of hysteresis with different EJ has been determined from the β − IB plots. We have modeled our experimental data with analytical model as well as simulation. From the simulation we found a change of factor of 15 in <Ne> over the measured EJ range but unfortunately we have not been able to determine it from the experiment. The numerical analysis has also generated the similar phase diagram as was found in experiment. The analytical 3 estimate of crossover curve also too fits well with measured IB-H - EJ curve (see Fig. 3) . In order to determine the common mode rejection ratio (CMRR) of a differential pair BOT we followed the scheme shown in Fig. 4. The common mode port is connected to the bases of the two BOTs and fed with varying voltages; simultaneously emitter currents of the two BOTs are recorded. We found that in order to achieve a CMRR, the matching of transconductances (gm) of two BOTs is sufficient. In our experiment we found a 20dB of CMRR even though gm of the two BOTs were not exactly equal (Fig. 5). We measured the input equivalent noise in β -mode and in gm – mode (c.f. Fig. 6) and estimated the Zopt to be 5 -10MΩ which matches with Zin ~ 6MΩ within a factor of 2 for the measured BOT devices. In short, BOT pair has the potential to use as a transconductance amplifier in cryogenic applications.

References: [1] J. Delahaye, J. Hassel, R. Lindell, M. Sillanpää, M. Paalanen, H. Seppä and P. Hakonen, Science 299 (2003),1045 [2] J. Hassel and H. Seppä, J. Appl. Phys. 97 (2005), 023904. [3] J. Sarkar, A. Puska, J. Hassel and P. J. Hakonen, arXiv: 1301.5546, (2013) [4] J. Sarkar, A. Puska, J. Hassel and P. J. Hakonen, arXiv: 1301.6053, (2013)


Figures:

10 kΩ VC

VC1 RC1

R1

IE1

I B1

VC

R

V

10 kΩ VCM

2Ω VC2 RC2

R

V R2

IE2

I B2

 

 

Figure 4: Measurement scheme used for measured of CMRR.

gm(μ S)

Figure 1: Scanning electron micrograph of a BOT. Collector, base and emitter are designated by C, B and E.

(a)

4 3 2 1

BOT # 1 BOT # 2

0 -1

-10 -20 -30

-0.5

0

0.5

1

1.5

VC (mV)

0

10

20 30 VCM (µV)

40

50

60

 

Figure 5:  (a) gm of the BOTs vs. collector bias VC. (b) Difference of absolute output currents of the BOTs plotted vs. voltage applied to the CM port. Straight line yields a CMRR of 20dB.  

i n (A/√ Hz)

Figure 2: The effect of IB on the I-V characteristics of BOT. With increasing IB, it clearly shows the approach towards bifurcation (right to left).  

IE2 )(pA)

 

30 (b) 20 10 0

Δ( IE1

-1

10

−13

−14

10

−15

10

(a)

1

−4

10

1

#1

en (V/√ Hz)

10

#2

−6

10

−8

10

(b)

1

 

Figure 3: Bifurcation threshold over the IB-H - EJ plane. #1 and #2 correspond to two samples measured in our experiment. Arrows denote the axis.

10 1

f (Hz)

10

2

 

Figure 6: Input referred current noise (in) in the current gain mode: red trace displays in with βE = 1. The blue curve depicts in measured at βE = 35. b) Input referred voltage noise (en) in the transconductance mode: the blue curve is obtained at gm = 10 nS while the red trace was measured at gm = 10 μS.  


Artificial antenna system based on one-directional FRET between AC and PY dyes within AlPO-36 nanochannels 1

1

2

2

Rebeca Sola Llano , Virginia Martínez-Martínez , Raquel García , Luis Gómez-Hortigüela , Joaquín 2 1 Pérez-Pariente , Íñigo López-Arbeloa 1

Departamento de Química Física, Universidad del País Vasco, UPV/EHU, Apartado 644, 48080, Bilbao, Spain. 2

Instituto de Catálisis y Petroleoquímica, ICP- CSIC. c/ Marie Curie 2. Madrid, Spain. rebeca.sola@ehu.es

Abstract The encapsulation of dyes into nanostructured ordered systems is a good tactic to provide new [1] functional materials with interesting optical, chemical and electrical properties. A great variety of solid matrices with different 1-, 2- or 3-dimension arrays are suitable to induce an anisotropy orientation on the guest molecules. In this sense, nanotubes and nanostructured tubular systems with elongated pores can act as a powerful ordering framework in one dimension for the guest species. Specifically, microporous aluminophosphates (AlPO) present zeolitic structures. The open nature of the structure of [2] zeotypes made them very interesting as host materials. The structure of these solids is built by a three-dimensional arrange of corner-sharing tetrahedra characterized by the presence of channels of molecular dimensions, where different molecules can be encapsulated. Therefore, aluminophosphates are good hosts to get 1D highly ordered ALPO/dye functional materials. They also exhibit different pore sizes depending on the type of AlPO4, which provides de advantage of choosing one type or another according to the application. These materials are usually prepared using organic compounds which are denominated structure directing agents (SDAs) that remain occluded within the structure at the end of crystallization. As dye molecules are not very different to typical SDAs used in zeolite-type hosts synthesis, this gives the opportunity to study the in situ incorporation of the dye during synthesis of the material. One of the types of aluminophosphates usually used as host is AlPO-5 (AFI) with 7.3 x 7.3 Å sized pores. However, in previous work it has been demonstrated that for xanthene-type dye guests, AlPO-5 system is high enough to accommodate H-type dimers resulting in a drastic quenching of the [3] emission of the sample. However, by a slight reduction of pore size of the host, i.e., AlPO-36 unidirectional channels with pore size of 7.3 x 6.4 Å, those dyes tend to conform J-aggregates. These aggregates are characterized by a fluorescent emission shift to the red range of the UV/Visible light spectrum. In this sense, PyronineY (PY) dye occluded into AlPO-36 crystals (ATS) show a multicolour emission under the optical fluorescence microscope (Figure A), from red (J-aggregates) to yellow [4] (monomers and aggregates) and to green (monomers). This material was thought to be interesting for light harvesting as the excitation energy can be transported along the crystal due to the particular arrangement of the PY species within the nanochannels: the green PY monomers can act as energy transfer donors to the red-shifted PY aggregates which behave as acceptor at the other end of the crystal needle (see Figure 1). In order to increase the range on UV/Visible collection range for a more efficient antenna system, Acridine (AC) dye, with a characteristic UV absorption band and blue emission is co-adsorbed together with the PY dye into the host material (Figure B). In this work, ATS crystals hosting two dyes are synthetize for different AC:PY relative concentrations in order to achieve an efficient energy transfer between the two dyes that will offer an antenna system working in the whole UV/Visible light range.


References [1] Schulz-Ekloff, G.; Wöhrle, D.; van Duffel, B.; Schoonheydt, R.A. Microporous Mesoporous Mater, 51 (2002), 91. [2] D. Brühwiler, G. Calzaferri, Microporous Mesoporous Mater. 72 (2004) 1-23. [3] R. García, V. Martínez-Martínez, L. Gómez-Hortigüela, I. López-Arbeloa, J. Pérez-Pariente, Microporous Mesoporous Mater.,(2013) http://dx.doi.org/10.1016/j.micromeso.2013.01.025 [4] V. Martínez-Martínez, R. García, L. Gómez-Hortigüela, J. Pérez-Pariente, I. López-Arbeloa (Submitted).

Figures

A

B

Figure: Real color fluorescence images of A) PY dye and B) AC and PY dyes into AlPO-36 crystals


Magnetization reversal process in Permalloy battlements 1

1

1

1

1

1

N. Soriano , C. Redondo , D. Navas , B. Mora , A. Arteche , F. Castaño , and R. Morales

2,3

1

Dpto. de Química-Física, Universidad del País Vasco UPV/EHU, 48940 Leioa, Spain. Dpto. de Química-Física, BCMaterials, Universidad del País Vasco UPV/EHU, 48940 Leioa, Spain. 3 IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain.

2

Contact e-mail: nastassiasemiramis.soriano@ehu.es

Patterned Permalloy (Py) submicrometric stripes were fabricated by interference lithography (IL) and magnetically characterized by vibrating sample magnetometry (VSM) [1, 2]. Photoresit templates +

generated by IL were used to deposit a Ti hard mask on a 100 nm thick Py layer. Then Ar ion etching transferred the Ti mask onto the Py layer (Figure 1). Line periodicity was set at 1.9 microns with an inter stripe distance of 700 nm. Four Py etching depths (dPy = 10, 15, 25 and 50 nm) were determined by atomic force microscopy (AFM) imaging (Figure 2). Magnetic hysteresis loops for different angles between the external field and the stripe axis were obtained at room temperature by VSM. Samples with low depth profile (dPy = 10 and 15 nm) show a progressive evolution from the easy axis to the hard axis of the ferromagnet. However deeper etching (dPy = 25 nm) reveals inverted hysteresis loops at specific angle conditions. The decreasing branch of the hysteresis loop crosses the magnetic field axis at positive values whilst the increasing branch shows a negative coercivity. For the deepest etching (dPy = 50 nm) two phases were observed in the hysteresis loops revealing a different approach to saturation for the stripes and the continuous part. Work supported by Basque Country Government grant Nanoiker11 and MICINN grants MAT201020798, FIS2008-06249.

References [1] Q. Xie, M.H.Hong, H.L. Tan, G.X. Chen, L.P. Shi, T.C. Chong, J. Alloy Compd. 449 (2008) 261. [2] S. Moralejo, F.J. Castaño, C. Redondo, R. Ji, K. Nielsch, C.A. Ross, F. Castaño, J. Magn. Magn. Mater. 316 (2007) e44.


Figures

Py

Ti mask 100 nm

dPy

1.9 Âľm

glass

Z (nm)

Figure 1. Cross section sketch of patterned samples

x (Âľm) Figure 2. AFM top view image (upper panel) and height profile through the gray line (lower panel) of a patterned sample


Study of the properties of indium doped zinc sulfide nanostructure Tzu-Ying Yang (1,*), Yi-Chang Li (1), Yen-Chih Chen (1), Chuan-Pu Liu (1,2) (1) Department of Materials Science and Engineering, National Cheng-Kung University, Tainan, Taiwan, 70101, REPUBLIC of CHINA (2) Research Center for Energy Technology and Strategy, National Cheng-Kung University, Tainan, Taiwan, 70101, REPUBLIC of CHINA piyonyang@hotmail.com Abstract In recent years, numerous efforts have been made on the research of nanostructured materials due to many specific properties of these materials. The distinct physical and chemical performance is one of the most popular research in the nanomaterials. By studying theses special features of nanostructured materials, we can develop the nano-devices and find the applications in the nanotechnology. Zinc sulfide is one of II-VI group semiconductors, and it has remarkable optical properties, thermal stability and diverse applications such as Field-emission, FET, UV-light sensor, gas sensor, and chemical sensor. We can improve the properties of these facilities with doping different elements: Mg, Cu, Co, Ga, Ni, etc [1]. There is rare research on In-doped ZnS, so we focus on this topic. In this study, self-assembled indium doped zinc sulfide nanostructures are synthesized by thermal evaporation method. The morphology and structure of the synthesized product are characterized by SEM, TEM, PL. SEM shows that In-doped ZnS have two types of nanostructures. One is nanosheet, the other is nanowire. TEM analysis shows that the In-doped ZnS nanostructures have the zinc blend structure. PL result demonstrates that the spectrum mainly includes two parts: a violet emission band centering at about 335 nm and a green emission band centering at about 530 nm.

References [1] X. Fang, T. Zhai, U. K. Gautam, L. Li, L. Wu, Y. Bando, and D. Golberg, Progress in Materials Science, vol. 56, pp. 175-287, 2011.

Figures

Fig. 1 SEM image (a) nanosheet (b) nanowire (c)(d) high-magnification of nanosheet

Fig. 2 TEM image (a) nanosheet (b) nanowire high-magnification image (c) nanosheet

Fig. 3 room temperature PL spectrum of the two types of In-doped ZnS


DNA-Wrapped Single-Walled Carbon Nanotubes based biosensors Oyarbide J.1, Argarate, N.1, Morin, F.O.1, Pardo W. A.2,3,4, Mir, M.2,3, Samitier J.2,3,4 1

Ciber-bbn, Tecnalia, Paseo Mikeletegi, 2, Parque Tecnológico 20009 San Sebastián, Spain. www.tecnalia.com 2 Ciber-bbn, NANOMED -IBEC, Instituto de Bioingeniería de Cataluña (IBEC). C/ Baldiri Reixac, 13, 08028 Barcelona. www.ibecbarcelona.eu 3 Laboratorio de Nanobioingeniería, Instituto de Bioingenieria de Cataluña (IBEC), Baldiri Reixac, 1012, Barcelona, 08028. 4 Departmento de Electrónica, Universidad de Barcelona (UB), Martí I Franques, 1, Barcelona, 08028 Contact: salud-024@tecnalia.com Abstract Deoxyribonucleic acid (DNA) biosensors, which employ an immobilized DNA as the biological recognition element, are currently under intense investigation due to their numerous potential applications. Among the DNA biosensors, the electrochemical DNA biosensors have been regarded to be excellent candidates for the rapid and inexpensive diagnosis of biological species of clinical interest, and for the compatibility with microfabrication technology [1,2]. In the last years, DNA functionalization of CNTs has attracted attention in various fields such as nucleic acid sensing and controlled deposition on semiconducting or conducting substrates [3]. This fact is due to the combination of the unique properties of the CNTs and the outstanding recognition capabilities of DNA [4]. In this sense, this work reports an optimized strategy for the wrapping of a specific DNA with and without a 5`SH-poly(GT)10 sequence labeled with a fluorescence group onto HNO3 treated Nanocyl 90 SWCNTs. This method is a relatively simple procedure that produces a strong π-π interaction between DNA (GT) strands and CNTs [5]. So, this functionalization does not disrupt the mechanical and electronic properties of the CNTs [6]. DNA-CNT hybrids were characterized by spectroscopic methods and measurement of the diameter change of SWCNT without or with DNA by AFM. Finally, we studied the possibility of using CNT-DNA hybrids in the fabrication of biosensors for selective recognition of DNA. Different biosensor configurations were tested with surface plasmon resonance (SPR), transmission electron microscope and atomic force microscope in order to select the most efficient and selective strategy for DNA detection. In conclusion, suitable CNT-DNA wrapping and surface protection procedure has been established for the design of a DNA-wrapped SWCNT based biosensor.

References [1] S.G. Wanga, Ruili Wang, P.J. Sellina, Qing Zhang. Biochemical and Biophysical Research Communications, 4, (2004) 1433–1437. [2] Ignác Capek. Dispersions Based on Carbon Nanotubes – Biomolecules Conjugates, Carbon Nanotubes- Growth and Applications, (2011) Dr. Mohammad Naraghi (Ed.), ISBN: 978-953-307-566-2, InTech. [3] Sobhi Daniela, Talasila Prasada Raoa, Kota Sreenivasa Raob, Sikhakolli Usha Ranib, G.R.K. Naiduc, Hea-Yeon Leeb, Tomoji Kawai, G.R.K. Naiduc, Hea-Yeon Leeb and Tomoji Kawai, Sensors and Actuators B, 122 (2007) 672–682. [4] Sanchez-Pomales, G., Pagan-Miranda, C., Santiago-Rodriguez, L., Cabrera, C. R. Carbon Nanotubes, (2010). Jose Mauricio Marulanda (Ed.), ISBN: 978-953-307-054-4. [5] Cao, Cet al., Materials Chemistry and Physiscs, 112, (2008) 738-741; [6] Sánchez-Pomales, G., Cabrera, C.R., Journal of Electroanalytical Chemistry, 606, (2007) 47-54.


Figures:

Figure 1. Schematic representation of wrapping procedure and the design of a DNA-SWCNT based biosensor.

Figure 2. Surface coverage of DNA with and without thiol (GT)10 strands, SWCNT and complementary DNA (Target) for the different systems by Surface Plasmon Resonance (SPR). • • • •

Unprotected platform: Biosensor without unfouling layer. MCH protected 2 steps platform: Biosensor with a mercaptohexanol monolayer generated after the DNA-SWCNT immobilization. MCH protected 1 step platform: Biosensor with a mixed monolayer of mercaptohexanol and DNA-SWCNT. Target: DNA-SWCNT hybridized with a complementary DNA


Uptake of polystyrene nanoparticles in CD34-HSC and CD34-DC investigated by flow cytometry and confocal microscopy 1,2

1,3

1

3

2

1,3

Birgit BarĂŠ , Sarah Deville , Lambrechts Nathalie , Marcel Ameloot , Peter Hoet , Jef Hooyberghs , 1 Inge Nelissen 1

Flemish Institute for Technological Research (VITO), Environmental Risk and Health Unit, Mol, Belgium 2 Catholic University Leuven (KULeuven), Lung Toxicology Unit, Leuven, Belgium 3 Biomedical Research Unit (BIOMED), Hasselt University, Diepenbeek, Belgium birgit.bare@vito.be

Although nanomaterials offer great opportunities for innovation and technological development, an increased human exposure implies that potential health impacts should be carefully addressed. The adjuvant activity of air pollution particles on allergic airway sensitization is well known, but a similar role of manufactured nanoparticles (NP) in allergic sensitization has not been clarified. Such mixed exposure situations may be relevant to daily life activities. During development, hematopoietic stem cells (HSC) develop into the different cells of the immune system, through subsequent steps of proliferation and differentiation. Manipulation of dendritic cell-differentiation can lead to a disturbed Th1/Th2 balance later in life [1]. However, to assess NP toxicity, it is important to understand whether and how NP are taken up by the cells. In this study, the uptake of manufactured nanoparticles by cord blood-derived CD34-HSC and immature myeloid dendritic cells (CD34-DC), that were in vitro differentiated from the CD34-HSC, was evaluated. The cells were exposed to 40 nm sized monodisperse polystyrene NP stained with fluorescent dyes. Uptake kinetics were evaluated by monitoring NP-uptake every hour, during 6 hours, with flow cytometry. Futhermore,the intracellular fate of NP was explored with confocal microscopy. CD34-DC and in CD34-HSC were shown to rapidly take up the majority of the NP within the first hour. Nevertheless, following one hour the total amount of NP inside the cell decreased. After 3 hours, an equilibrium was set. Future experiments will focus to unravel the uptake mechanisms in CD34-DC and CD34-HSC. Insights in NP uptake and their intracellular fate contribute to elucidate the possibile interference of NP with normal cell function. References [1] Koga Y, Matsuzaki A, Suminoe A, et al. Immunol Lett 116 (2008) 55-63.


Molecular Characterization of the Effects of the Nanoparticle Interface on the Hydration Water 1

2

1

Marco Bernabei , Paul Martin ,Giancarlo Franzese and Eugenia Valsami-Jones

2

1) Departament de FĂ­sica Fonamental, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain 2) School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT UK marcobernabei@gmail.com

Abstract In the framework of a multiscale approach to study the protein-nanoparticle interaction in solution, we study here how to include the effects of the nanoparticle (NP) interface on the hydration water. From atomistic molecular dynamic simulations of a single nanometer-size solute in water, we study the hydration structure of different Silver NP. We analyze the behavior of the dipole moment and the potential energy of water molecules as a function of the distance from the surface, for different NPs shape. We show how our results can be used to tune the interaction parameters of a 3D coarse-grained model for water, in order to account of the interaction of water molecules at the NP surface. Our goal is to develop a coarse-grained model of the NP-protein solution with explicit water that would allow us to perform large scale simulations, something essential to compare simulations with experiments and to lead to useful model.


neceAntimicrobial effect of coated leather based on silver@silica nanocomposites M. Isabel Maestre-López, Federico J. Payá-Nohales, Francisca Arán-Ais, Miguel A. Martínez- Sánchez, César Orgilés-Barceló, Marcelo Bertazzo INESCOP. Footwear Research Institute. 03600 Elda (Alicante). Spain. mbertazzo@inescop.es Abstract Nowadays, the antimicrobial properties of different materials are a significant feature for a wide range of products, not only in the healthcare sector, but also in sports, housekeeping, etc. In the case of footwear, microorganisms, such as bacteria, fungi and viruses, are likely to proliferate in the shoe environment under appropiate temperature and humidity conditions. Their multiplication is the cause for the development of odour in areas that are worn close to the skin and also for the development of infections in the case of pathogen organisms. Consequently, the demand for new and different coatings for footwear materials that enable good antibacterial protection has increased. Currently, existing biocides include some antimicrobial agents, most of them being organic compounds, that are extremely irritant, harmful and toxic for the environment and human health. Therefore there is a growing interest in finding ways to formulate new types of safe and ecological materials. Such problems and needs have currently led to resurgence in the use of silver-based (Ag) antiseptics which have been used for centuries as antimicrobial agents for the treatment of burns, water treatment 1 processes and wound disinfection . Today, these properties have been enhanced through nanotechnology, which has allowed the size of metal nanoparticles to be modularly and accurately reproduced. Previous studies revealed high antimicrobial activity of silver nanoparticles (AgNPs) against a broad spectrum of microorganisms. The advantage of the antimicrobial mechanism of silver is the ability to produce an antibacterial effect at very low concentrations (oligodynamic effect). Therefore, this work is aimed to develop coated leathers with enhanced antimicrobial properties, thus providing a solution to avoid the problems mentioned above. To achieve this objective, nanosilver 2 3 colloidal solutions were synthesised using different reductors such as borohidrure , gelatine/glucose 4 and an aloe vera phenolic extract (Figure 1). The first one is a control of the others, which were considered as green methods because they do not require the use of organic solvents. In all cases, the formation of Ag-NPs was further determined by using UV–visible spectroscopy (Figure 2) as a function of time. Furthermore, in order to improve nanoparticle stability and avoid their aggregation, silver-silica 5 nanocomposites were synthesised by a modified Stöber method . In this study, we evaluated the properties of a novel silver-silica nanocomposite used as an antimicrobial additive for leather and compared its efficacy to that of AgNPs. A representative transmission electron micrograph of AgNPs and silver-silica nanoparticles is shown in Figure 3A and 3B. The nanocomposite consists of aggregate silica matrix particles where silver metal particles are located within the matrix and are also embedded within the matrix. The silver nanoparticle morphology and dispersability were evidenced by transmission electron microscopy (TEM) measurement. AgNPs embedded within the silica matrix were also evaluated by TEM and EDX analysis. In addition, scanning electron microscopy (SEM) was performed on the AgNPs-silica nanospheres, allowing also the size of the nanospheres to be determined. Synthesised AgNPs and Ag-silica nanoparticles were applied to different leathers to obtain antimicrobial coatings. The treated leathers studied include metal-tanned leather (chrome, titanium, aluminium) and oxazolidine-tanned leather. For this purpose, leather samples were treated with the corresponding silver solutions by applying 50 L of the solution on the grain side, and 50 L on the flesh side, allowing them to dry for at least 24h at room temperature. In order to verify the presence of AgNPs and AgNPs-silica nanocomposites on the leather matrix, SEM analysis was performed on both the grain and flesh sides and also, with the leather matrix, on the side of criofractured leather samples to test nanoparticles and nanospheres penetration (Figure 3C). Finally, the antimicrobial activity of the treated leathers was tested by means of liquid and solid (agar diffusion) antibacterial tests against both gram positive (Staphyllococcus aureus and Bacillus subtilis) and gram negative bacteria (Escherichia coli and Klebsiella pneumoniae). All the different treated leather samples showed a strong antibacterial activity in liquid medium (Figure 4A). In agar diffusion test, titanium- and aluminium-tanned leathers showed also a synergistic effect along with silver on B. subtilis survival (Figure 4B).


The results show that the functionalisation of leather with AgNPs, and especially with AgNPs-silica nanocomposites represents a promising alternative to create leather with enhanced antifungal and antimicrobial properties. Some advantages of the silver-silica nanocomposites are the dispersion of the discrete silver particles throughout the silica (which prevents agglomeration of the silver particles), the small diameter of the silver particles (which results in a large surface area and release of a large + amount of Ag , which results in high antimicrobial efficiency), and the small size of the silver-silica nanocomposite (which allows the material to be uniformly dispersed and readily incorporated into leathers but also into a variety of substrates, including synthetic fibres, coatings, plastics, etc.). A further advantage is that the immobilization of silver nanoparticles within the silica structure limits the potential for release and disposal of the nanoparticles themselves. This property may be highly desirable because of the possible abilities of nanoparticles to go through biological membranes and other barriers. Acknowledgements: IVACE (Instituto Valenciano de Competitividad Empresarial). Project Reference: IMDEEA/2011/46. References QL Feng, Wu J, Chen GQ, Cui FZ, Kim TN, Kim JQ Journal of Biomedical Material Research 52 (2000): 662. 2 J.A. Creighton, C.G. Blatchford and M.G. Albrecht. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 75 (1979): 790-798. 3 Majid Darroudi, Mansor Bin Ahmad, Abdul Halim Abdullah, Nor Azowa Ibrahim. International Journal of Nanomedicine 6 (2011):569–574. 4 Zhang, D. Yag, Y. Kong, X. Wang, O. Pandoli and G. Gao. Nano Biomedicine and Engineering, 2(4) (2010): 252-257. 5 W. Stöber and A. Fink. “Controlled growth of monodisperse silica spheres in the micron size range”. Journal of Colloid and Interface Science, 26 (1968): 62-69. 1

Figures

Fig. 1. Nanosilver and silica nanocapsules obtained with the different synthesis methods.

Fig. 2. Uv-vis characterisation of the AgNPs solutions synthesised with Aloe vera extract, at different periods of the synthesis process.

Fig. 3. TEM micrographs corresponding to: A) AgNPs colloidal solution; B) Ag-silica nanocomposites; C) SEM micrograph corresponding to leather fibres treated with Ag-silica nanocomposites.

Fig. 4. Liquid NB medium assay showing the antibacterial effect of aluminium-tanned leather with all the 6 AgNPs containing solutions against Bacillus subtilis (BS) (left). Petri dish showing the antimicrobial effect of titanium-tanned leather treated with silica-coated AgNps against BS (right).


Magnetic field assisted micro contact printing: a new concept of fully automated and calibrated process a

a

a

CAU Jean-Christophe , LAFFORGUE Ludovic , NOGUES Marie , PAVEAU Vincent a

a

INNOPSYS, Carbonne, 31390, France e-mail: jc-cau@innopsys.fr

Keywords: Micro contact printing, Soft lithography, Multiplexing, Standardization, Magnetic stamp

Abstract Micro contact printing (μ-CP) ([1] [2]), is a simple and cost-efficient technology well established worldwide. This technology opened new opportunities for various applications such as protein or cellular patterning, surface chemistry, physics, semiconductor … Interestingly, though its wide application range, there is no standardized or calibrated system permitting to transfer scientific research to industrial applications. Indeed, one of the critical points in µCP is the control of the force applied on the stamp during the printing step. The technologies developed are always based on a mechanical force (air [3] or hydraulic [4] pressure or mechanical devices [5][6]). The drawback of this choice is that the stamp geometry has to be adapted to the mechanical system. In this work, we propose a new concept: the magnetic field assisted micro contact printing. For that, we integrated on the upper side of a stamp a quantity of iron powder (25% weight). The stamp became sensitive to a magnetic field. So, changing the magnetic field strength permits to adjust the force applied. Thanks to magnetic force simulations, corroborated by experimental measurements (fig .1), we found that the force can be tuned by the distance between the stamp and the magnet (from 0 to 15 mm) or by the voltage applied on the solenoid (from 0 to 50 V). We used the layer in contact with molecules or nano-objects without iron powder and composed by sylgard 184 in order to be in the same configuration as the previous scientific studies. In addition to the tuned application force, our design enables to transport the stamp during the process, leading to a fully automated process, ready for industrial applications. Our system, INNOSTAMP40 is thus fully automated and calibrated for better standardization of the technology. This equipment is composed of different modules (fig 2) which correspond to the elementary steps of the µCP process: loading, inking, alignment, drying, stamping, cleaning and unloading zone. The loading zone can accept up to 4 different stamps with maximum dimensions: 26mm*75mm (glass slide dimensions). There is a temperature regulation on the inking zone (0°C to 50°C) to reduce evaporation. The alignment has a precision of 10µm. The drying zone is design to prevent pollution. The calibrated stamping force can be adjusted. We reported the evolution of the printing quality when the force applied increases. The cleaning zone is composed of tanks that can be filled with acid or basic solutions, or solvents. All the steps can be configured thanks to the ergonomic software of INNOSTAMP40. We demonstrated the genericity of this technique on fig 3. We can use stamp geometry from 1cm² to 19cm² (glass slide format) with normal or macrostamp formats [7] without any mechanical adaptation. These formats permits to ink a stamp in one step with different inks from a well plate (384 or 1536 wells) commonly used in biology laboratories. It shows the adequacy between the INNOSTAMP40 and biological applications (biochip, microarray, lab-on-chip …) that need multiplexing. Low-cost stamp and macrostamp have been produced. In the latter case, the iron powder could be added at different position into the macrostamp : only on the pad, on the pad and the dot, etc. (fig 4). We have studied the advantages and drawbacks of each configuration. In conclusion, we have demonstrated that the concept of magnetic stamp permits to propose a new fully automated and calibrated micro contact printing system. This system, INNOSTAMP40, creates a bridge between the lab experiment and its industrial applications.


References [1] Y.N. Xia, E. Kim, G.M. Whitesides, J. Electrochem. Soc. 143 (3) (1996) 1070–1079. [2] E. Delamarche, H. Schmid, H.A. Biebuyck, B. Michel, Adv. Mater. 9 (1997) 741. [3] R. Cracauer, R. Ganske, C. Goh, J. Goh, A. Liederman, R. Loo, P. Tam patent WO2005/061237 (2004) [4] ] K Choonee and R R A Syms J. Micromech. Microeng. 21 (2011) 085013 [5] S. Hall, R.Nunes, R. Fair, W. Surovic, I. Lovas, R. Emmans patent US2004/0011231 (2002) [6] G. Maracas, T. Burgin, T. Mance patent : US5937758 (1997) [7] H. Lalo, J-C. Cau, C. Thibault, N. Marsaud, C. Severac, C. Vieu, , Microelectronic Engineering, Volume 86, Issues 4–6, (2009) 1428-1430

Figures

2

4 6

1 3

5 7

1

stamp loading

4 drying

2

alignment

5

printing

3

inking

6

cleaning

7 Stamp unloading

Figure 1. Evolution of the applied force (g) as a function of the distance between the magnetic field source and the magnetic stamp.

Figure 2. Schematic INNOSTAMP40.

Figure 3. Pictures of “regular” stamp and macrostamp, and an example of print (Cy3 fluorescent dye).

Figure 4. Schematic views and corresponding pictures of different stamp configurations. Green : PDMS, blue : PDMS mixed with iron powder

view of

the automate


Sweet Nanomaterials: Carbohydrate-Coated Carbon Nanotubes and Glyconanosomes as Advanced Nanovectors for Drug Delivery. 1

1

1

2

3

Juan-José Cid , Mohyeddin Assali , Manuel Pernía-Leal , Inmaculada Fernández , Miguel Muñoz , 3 1 Ralf Wellinger and Noureddine Khiar * 1

Grupo de Química Bioorgánica, Instituto de Investigaciones Químicas (IIQ), C.S.I.C. and Universidad 2 de Sevilla. C/ Américo Vepucio 49, 41092, Seville, Spain. Departamento de Química Orgánica y 3 Farmacéutica, Universidad de Sevilla. C/ Profesor García González 2, 41012 Seville, Spain. Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), 41092 Seville, Spain. khiar@iiq.csic.es 1

Single-walled carbon nanotubes (SWCNTs) have received an unrivalled interest as consequence of their unique structural, mechanical, electrical, and optical properties that make them promising 2,3 candidates for biomedical applications. To overcome their inherent insolubility in biological media various approximations, including covalent and non-covalent functionalization, have been developed. Nevertheless, these methods suffer from important drawbacks such as the low stability of the obtained aggregates or the disruption of -electronic character of the CNTs sidewalls. In order to solve these problems, we have recently reported a bottom-up approach based on the supramolecular selforganization of diacetylenic-based glycolipids on the SWCNTs sidewalls, followed by photo4-7 polymerization to form polydiacetylene glycolipid-coated nanotubes. By using this methodology, the resulting nano-assemblies are water soluble, highly stable and show a biomimetic and multivalent presentation of carbohydrates on their surface, and besides, without altering the physico-chemical 7 properties of the inner tube.

Figure 1. Supramolecular self-assembly and photopolymerization of diacetylenic-based glycolipid 1 on the nanotube surface, and TEM characterization showing the abacus-like topology of the nanoconstructs. In the present communication, we are aimed at discussing: a) the synthesis and characterization of glyconanoring-coated SWNTs with 1-type glycolipids (Figure 1), b) their selective binding to lectins (Figure 2A) and their specific aggregation of uropathogenic Escherichia coli bacteria (Figure 2B), and c) the glyconanoring sliding out of the carbon nanotubes to afford a new class of disk-shaped amphiphilic biomaterials named glyconanosomes (GNSs) (Figure 3). Hence, the ability of GNSs to encapsulate lipophilic molecules will be presented, together with comparative results of in vitro activity of their inclusion complex with camptothecin (CPT) (GNS/CPT) as rd nanoparticle-based drug delivery systems of 3 generation for the controlled delivery of CPT in the 8 inhibition of carcinogenic cell proliferation.


Figure 2. Specific interaction of SWCNT/glycolipids with lectins, and application in the selective aggregation of uropathogenic bacteria.

Figure 3. Synthesis of glyconanosomes (GNSs) by the ultra-sonication-induced sliding out method and application in the water solubilization of the hydrophobic C60, perylene-bisimide and the cytotoxic camptothecin (CPT). References [1] Iijima,S., Nature, 354 (1991) 56. [2] X. Chen, A. Kis, A. Zettl, C.R. Bertozzi, Proc. Natl. Acad. Sci. U.S.A., 20 (2007) 8218. [3] Z. Liu, C. Davis, W. Cai, X. Chen, H.J. Dai, Proc. Natl. Acad. Sci. U.S.A., 5 (2008) 1410. [4] M. Assali, M. Pernía-Leal, I Fernández, R. Baati, C. Mioskowski, N. Khiar, Soft Matter, 5 (2009) 948. [5] N. Khiar, M. Pernía-Leal, R. Baati, C. Ruhlmann, C. Mioskowski, P. Schultz, I. Fernández, Chem. Commun. 27 (2009) 4121. [6] M. Assali, M. Pernía Leal, I. Fernández, R. Baati, N. Khiar, Nano Res., 11 (2010) 764. [7] M. Pernía Leal, M. Assali, I. Fernández, N. Khiar, Chem. Eur. J., 6 (2011) 1828. [8] M. Assali, J.-J. Cid, M. Pernía-Leal, M. Muñoz-Bravo, I. Fernández, R. E. Wellinger, N. Khiar, ACS Nano, 3 (2013) ASAP (DOI: 10.1021/nn304986x).


Engineering of near IR fluorescent albumin nanoparticles for optical detection of colon cancer Sarit Cohen, Shlomo Margel The Institute of Nanotechnology and Advanced Materials, Department of Chemistry, Bar-Ilan University, Ramat-Gan, 52900, Israel saritcohen@gmail.com Abstract The use of near-infrared (NIR) fluorescence imaging techniques has gained great interest for early detection of cancer because water and other intrinsic biomolecules display negligible absorption or 1-3 autofluorescence in this region . The present study describes the synthesis and use of NIR fluorescent albumin nanoparticles as a diagnostic tool for detection of colon cancer. These fluorescent nanoparticles were prepared by a precipitation process of human serum albumin (HSA) in aqueous 4 solution in the presence of the NIR dye CANIR . Leakage of the encapsulated dye into PBS containing 4% HSA or human bowel juice was not detected. This study also demonstrates that the encapsulation of the NIR fluorescent dye within the HSA nanoparticles reduces the photobleaching of the dye significantly. Tumor-targeting ligands such as peanut agglutinin (PNA), anti-carcinoembryonic antigen (anti-CEA) antibodies and tumor associated glycoprotein-72 monoclonal (anti-TAG-72) antibodies were covalently conjugated to the NIR fluorescent albumin nanoparticles via the carbodiimide activation method. Specific colon tumor detection was demonstrated in a chicken embryo model and in a mouse model. The bioactive NIR fluorescent albumin nanoparticles also detected invisible tumors that were 5 revealed as pathological only subsequent to histological analysis . These results may suggest a significant advantage of NIR fluorescence imaging using NIR fluorescent nanoparticles over regular colonoscopy.

References [1] Amiot CL, Xu S, Liang S, Pan L, Zhao JX, Sensors, 5 (2008) 3082-3105. [2] Khullar O, Frangioni JV, Grinstaff M, Colson YL, Seminars in thoracic and cardiovascular surgery, 4 (2009) 309-315. [3] Luo S, Zhang E, Su Y, Cheng T, Shi C, Biomaterials, 29 (2011) 7127-7138. [4] Cohen S, Pellach M, Kam Y, Grinberg I, Corem-Salkmon E, Rubinstein A, Margel S, Materials Science and Engineering: C, (2012) 923-931. [5] Cohen S, Margel S, Journal of Nanobiotechnology, 1 (2012) 36-44.


Figures

Fig. 1 Relative fluorescence intensity of the LS174t, HT29 and SW480 tumors labeled with non-conjugated (HSA), PNA-conjugated (PNA– HSA), and anti-CEA-conjugated (anti-CEA-HSA) nanoparticles. Nonconjugated (HSA) nanoparticles labeled all three tumor types with only slight differences between them (a). The highest fluorescence was obtained for tumors treated with biomolecule-conjugated nanoparticles in which there is upregulation of the corresponding receptors (b). The lowest fluorescence was obtained for tumors treated with biomoleculeconjugated nanoparticles with a comparative downregulation of corresponding receptors (c). Data is presented as the mean±SE. Values not sharing a common letter (a–c) differ significantly from each other (p˂0.05). The representative calculations are an average of 3 experiments.

Figure 3 SEM images of sections from LS174t tumor implants of a mouse colon untreated (A) and treated (B) with the anti- CEAconjugated NIR fluorescent HSA nanoparticles.

Figure 2 Logarithmically scaled fluorescent and grayscale images of typical LS174t (A) and HT29 (B) colon tumor cell lines treated with nonconjugated (1) and anti-CEA (2) and anti-TAG-72 (3) conjugated NIR fluorescent HSA nanoparticles: (4) represents untreated tumor cell lines; (C) represents typical colons of healthy mice treated with non-conjugated (1) and anti-CEA (2) and anti-TAG-72 (3) conjugated NIR fluorescent HSA nanoparticles. 44 mice (each set of experiment was done with 4 mice) were anesthetized and treated with 0.1% particle dispersion in PBS, via the anus. 20 min later the colons were extensively washed with PBS and were then allowed to recover for 4 h. The colons were then removed and treated as described in the experimental part.


NOBLE METAL NANOPARTICLES USED AS CARRIERS SYSTEMS FOR NSAIDs DRUGS: SEF, RELEASE AND BINDING P. Sevilla1,2, E. Corda2, M. Hernandez2, J.V. Garcia-Ramos2, C. Domingo2 Departamento de Quimica-Fisica, Facultad de Farmacia, UCM, 28040 Madrid, Spain1, Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid, Spain2 elisacorda@iem.cfmac.csic.es

INTRODUCTION Targeted drug delivery constitutes, actually, one of the most important research fields. It is necessary to maximize the therapeutic effects jointly with a minimization of the undesired secondary ones. The use of noble metal nanoparticles as drugs nanocarriers presents two principal advantages, firstly they are able to transport several therapeutic molecules adsorbed on their surface and secondly, due to the presence of Localized Surface Plasmon Resonances, an enhancement of the spectroscopic signals of the molecules carried is produced thus permitting to observe them in their traverse through the body to the specific disease tissues. In this work we present part of our research using noble metal nanoparticles as drug delivery systems, based on our previous studies [1, 2]. On one side we show SEF (Surface Enhanced Fluorescence) results of systems formed by several NSAIDs (Non-Steroidal AntiInflamatory DrugS), piroxicam (PX), ketorolac (KT) and indomethacin (IM) and Au nanoparticles. On the other side, and using Ag nanoparticles, we also present results of the binding constant of the albumin-drug system when protein molecules are adsorbed on Ag nanoparticles, and those of the release of the molecules from silver nanostructures. EXPERIMENTAL METHODS UV-vis absorption spectra were obtained using a Varian Cary 500 UV-Vis spectrophotometer and quartz cells of 1 cm of path length. Fluorescence: steady-state experiments were recorded on a Perkin Elmer LB50. SEF spectra measurements were carried out on a Renishaw In via Raman Microscope, using excitation wavelength of 325 with a spectral resolution of 2 cm-1. The colloid used for SEF experiments was prepared by chemical reduction of metal nitrate with hydroxylamine hydrochloride (Ag) or sodium citrate (Au). RESULTS AND DISCUSSION Au: fluorescence experiments of the drugs adsorbed on Au nanoparticles performed at several pH´s indicate that PX shows SEF at pH=2 and quenching for pH=1, 4 or 7, thus indicating simultaneously adsorption and aggregation of the molecules at acidic pH. IM exhibits SEF at pH=3 and very little SEF at pH=6, what indicates the presence of aggregates at acidic pH, and KT shows quenching at the basic and acidic pH´s studied because of non-aggregation process at any pH used. These results permit a change in the solubility of the drugs with the consequent change in the bioavailability. Ag: we have studied the binding constants of the drug to serum albumin, the most important drug carrier in the blood, when protein is in solution and when protein is adsorbed on silver nanoparticles. Results for the binding constant in presence and in absence of fatty acids indicate that KT and IM present higher Kbinding of the drug when protein is adsorbed on the metal surface and the maximum of drug binding increases with metal for IM but decrease for KT. Finally the dialysis of Ag nanoparticles-drug systems has permitted us to study the release of the drugs from the metal surface. Results indicate that KT establishes stronger bonds than PX.


CONCLUSIONS We have obtained SEF data from antiinflamatory molecules PX and IM adsorbed on Au nanoparticles, thus increasing their solubility in water solution; on the other hand for KT we have obtained quenching of the fluorescence indicating that there is no aggregation and consequently the big solubility of the drug decreases. Silver nanoparticles are also able to transport the drugs bound to the albumin forming the complex protein-drug. The presence of the nanoparticles changes the binding constants of the systems studied. These data constitute a preliminary study about the knowledge of the physical-chemistry properties of the drugs adsorbed on noble metal nanoparticles surface that will allow us to deep in the design of new drug delivery systems with potential to improve the clinical efficacy of the therapeutic effect of the antiinflamatory molecules used.

REFERENCES [1] P. Sevilla, F. Garcia-Blanco, J.V. Garcia-Ramos, S. Sanchez-Cortes, Phys. Chem. Chem. Phys., 11 (2009) 8342-8348. [2] R. De-Llanos, S. Sanchez-Cortes, C. Domingo, J. V. Garcia-Ramos, P. Sevilla, J. Phys. Chem. C, 115 (2011) 12419-12429.

This work has been financially supported by Comunidad de Madrid (MICROSERES II S2009TIC-1476), MINECO (FIS2010-15405) and UCM (Research Group 950247).


Selective electrical detection of Fe(III) ions with a BioFet sensor Tuyen Duc Nguyen, Racha El Zein, Jean Manuel Raimundo, HervĂŠ Dallaporta, and Anne M. Charrier Aix-Marseille University, CINaM-CNRS, Campus de Luminy, Case 913, 13288 Marseille, France dallaporta@cinam.univ-mrs.fr Abstract The development of biosensors is a hot issue in the biomedical and environmental fields, whether it is for the diagnostic or the monitoring with the detection of specific markers (molecules, ions, bacteria, viruses, etcâ&#x20AC;Ś). The development of bioelectronics has been a breakthrough is that field with the development in particular of field effect transistors based biosensors. This type of sensors fulfil many of the nowadays needs in terms of fast response, miniaturization, handiness of the detection process, transportation, high throughput fabrication, and absence of labelling. Here we report the development of such sensor for the detection of ferric ions in solution. Iron is ubiquitous and plays versatile roles in many important metabolic processes, biological materials and environmental samples. We report here the high performances of a new MOS-type field effect transistor developed for the detection of ferric ions in solution (fig. 1). We demonstrate the detection of ferric ions down to 50 6 fM (6Ă&#x2014;10 Fe(III) ions or 0.6 fg) in a quantitative way with a logarithmic dependence of the measured signal on the concentration of ferric ions in the analyte (fig. 2 and 3). To our knowledge, this is one of the best sensitivity ever reported for ions using such type of sensors. These performances are due to the unique sensing layer of our transistor. It is based on an end-capped lipid monolayer with a 1-4 hydroxypyridinone derivative. In addition to playing the role of interface between the transduction part of the sensor and the analyte, the lipid monolayer is also used as ultra-thin gate dielectric (3nm 5-7 thick) in the transistor . Using such thin dielectric layer not only improves the sensitivity of the sensor by enhancing the electric field across the transistor gate dielectric but also offers the possibility to work at low operating voltage, which is a major asset for biosensing and the detection of organic molecules. In addition this lipid monolayer appears to be rather inert to ions and does not require passivation to improve the specificity. Both specificity and sensitivity of the sensor also rely on the hydroxypyridinone derivative which shows to be highly specific to ferric ions. In particular the speciation between ferrous and ferric ions is clear (fig.3). Moreover this sensor is versatile and can be adapted to a whole variety of applications in biomedicine or for the monitoring of the environment and of water distribution and treatment.

References 1- F. Moggia, H. Brisset, F. Fages, C. Chaix, B. Mandrand, M. Dias and E. Levillain, Tetrahedron Lett., 2006, 47, 3371; 2- F. Moggia, F. Fages, H. Brisset, C. Chaix, B. Mandrand, E. Levillain and J. Roncali, J. Electroanal. Chem., 2009, 626, 42; 3- M.A. Santos Coord. Chem. Rev., 2002, 228, 187; (d) G.J. Kontoghiorghes, Br. Med. J., 1988, 296, 1672; 4- R.C. Hider, A.D. Hall, Clinical useful chelators of tripositive elements, in: G.P. Ellis, G.B. West (Eds.), Progress in Medicinal Chemistry, vol. 28, Elsevier, New York, 1991, 41. 5- A. Charrier, T. Mischki and G.P. Lopinski, Langmuir, 2010, 26, 2538. 6- R. El Zein, H. Dallaporta, A.M. Charrier, J. Phys. Chem. B, 2012, 116, 7190. 7- C. Dumas, R. El Zein, H. Dallaporta, A.M. Charrier, Langmuir, 2011, 27, 13643.


Figures

Figure 1: Schematic view of the BioFet device. A SU-8 resist is used to get the electrical insulation between drain, source and gate

Figure 2: Transfer characteristic of the BioFet sensor versus ferric ion concentration in the analyte. The insert gives the variation of the IDS current versus ferric concentration

Figure 3: Variation of the IDS current versus different ion concentration


Magnetic Hyperthermia experiments with previously characterized Magnetite Nanoparticles. E. Garaio,a I. Castellanos,b F. Plazaola,a M. Insausti,b J.A. Garcia,c J.M Collantes,a J.J. EchevarriaUraga,d I. Garcia-Alonso Montoya,e I. Gil de Muro,b B. Herrero de la Parte e Elektrizitatea eta Elektronika Saila, UPV/EHU, Leioa, PK 48940, Spain b Kimika Ezorganikoa Saila, UPV/EHU, Leioa, PK 48940, Spain c Fisika Aplikatua II Saila, UPV/EHU, Leioa, PK 48940, Spain d Servicio de Radiología. Hospital de Galdakao-Usánsolo. e Departamento de Cirugía y Radiología y Medicina Física. Facultad de Medicina. UPV/EHU a

eneko.garayo@ehu.es Abstract Magnetite nanoparticles have been widely used because of their applications in magnetic hyperthermia. This technique is based on the exothermic properties of magnetic materials under the influence of an alternating current magnetic field. The localization of magnetic nanoparticles and posterior heating of tumor cells without damaging normal tissues is a promising cancer thermotherapy. Within this scope, firstly we are interested in the preparation of monodispersed nanoparticles with an appropriate capping and different size distributions and secondly, in the measurement of the heat generated by the nanoparticles in terms of the specific absorption rate (SAR). Samples have been obtained by different synthetic methods and have been characterized by transmission electron microscopy and thermogravimetric measurements. Using a self-designed electromagnetic applicator, the specific absorption rates of the cited nanoparticles have been measured under rf magnetic field. Using the same apparatus, several magnetic hyperthermia experiments have been performed. Different nanoparticle samples were injected into several mice livers while rf-magnetic fields ranging from 600 to 900 kHz were applied to the hole system. The temperature time evolutions in several point of liver as well as in the surrounding medium were measured while magnetic field was applied (Fig. I). The observed temperature increments are discussed and related to the previously characterized properties of magnetite nanoparticles.

Figure I. Measured temperature evolution in one liver.


Study of the toxicity and penetration of mesoporous silica nanoparticles in the model insect Blattella germanica a

a

b

b

a

M.D. Agustin-Moya , M.A. Ochoa-Zapater , F.M. Romero , A. Ribera , A. Torreblanca , M.D. Garcerá a

a

Departamento de Biología Funcional y Antropología Física, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain. b Instituto de Ciencia Molecular, Universitat de València, Catedrático José Beltrán, 2. 46980, Paterna, Valencia, Spain. Maria.D.Garcera@uv.es

Abstract Nanotechnology is considered as one of the key technologies of the 21st century and promises revolution in our world. Studies have revealed that the same properties that make nanoparticles (NPs) so unique could also be responsible for their potential toxicity [1]. Nanotoxicology is a branch of bionanoscience which deals with the study of toxicity of these nanomaterials. Nanotoxicological studies are intended to determine whether and to what extent these properties may pose a threat to the environment and to human beings. Mesoporous silica NPs are made of an inert material, but their toxicity as NPs has not been investigated. In the present study we investigated the toxicity of mesoporous silica NPs in order to use them as carriers for drug delivery. The NPs have been applied to a model animal, the insect Blattella germanica, analysing the extent of NPs penetration in the insect. The synthesis of silica NPs was based on a modification of a previously reported protocol [2], using shorter reaction times and including the addition of the fluorophore rhodamine B [3]. The synthesized NPs were administered to the insects using the Potter Tower. Mortality rates were recorded after 72 hrs and survivors were frozen at -80ºC until use. Finally, the insects were dissected; the tracheae and the fat tissue were analysed using an Olympus FV1000 fluorescence confocal microscope with a 60x objective. Although no toxicity was observed after NPs application, the results confirmed the presence of the silica nanoparticles on the fat tissue and inside and outside the trachea. It was also observed that they could pass through the walls of the tracheae. Acknowledgements: This work has been supported by grant AGL2010-21555 from the Ministerio de Economía y Competitividad. References [1] S. Arora, J.M. Rajwade, K.M. Paknikar. Toxicol. Appl. Pharmacol. 258: 151-165 (2012). [2] T. Suteewong, H. Sai, J. Lee, M. Bradbury, T. Hyeon, S.M. Gruneref, U. Wiesner. J. Mater. Chem. 20: 7807-7814 (2010). [3] C.I. Zoldesi, C.A. van Walree, A. Imhof. Langmuir 22: 4343-4352 (2006).

Figures

Fig.1. TEM characterization and frequency of size distribution of silica nanoparticles marked with rhodamine B.


A

10Âľm

B

C

Fig.2. Confocal microscope image: (A) NPs at the tracheae and fat tissue; (B) Dimensional image of the trachea with nanoparticles inside and outside; (C) Cross-section of trachea showing how the nanoparticle go through it.


Clotrimazole blocks apoptosis on human erythrocytes when exposed to lead(II): an AFM imaging study Aritz B. García-Arribas, Hasna Ahyayauch, Alicia Alonso, Félix M. Goñi. Unidad de Biofísica (Centro Mixto CSIC,UPV/EHU), and Departamento de Bioquímica, Universidad del País Vasco (UPV/EHU), Leioa, Spain. Correspondence: aritzgarciaar@hotmail.com Abstract Atomic force microscopy (AFM) has been applied to the characterization of human red blood cells (RBC) at 23ºC. Erythrocytes were obtained by centrifugation and washing of blood samples extracted from healthy donors, attached to ethanol-washed glass coverslips and fixed with glutaraldehyde to obtain AFM images (Figure 1), so that cell diameters and thicknesses 2+

could be measured. When Pb

was applied at 10 µM at 37ºC for 10 minutes (all lead

incubations were previous to fixation), erythrocytes underwent a morphological change due to the start of RBC apoptosis (eryptosis), losing their typical biconcave form to become essentially planar, including phosphatidylserine (PS) exposure to the outer monolayer of the cell 2+

membrane. Moreover, when Pb

incubation was increased to 1 hour, erythrocytes became

totally spherical (spherocytes) (Figure 2). A progressive decrease in diameter was observed. Spiculated echinocytes appeared during this process when the incubation time was over 10 minutes. 2+

Interestingly, the use of clotrimazole, a suggested anti-apoptotic agent, inhibited Pb

effect, completely preserving morphology even after 20 minutes of lead exposure. Furthermore, when clotrimazole-treated RBC were exposed to lead overnight, morphology was still preserved (no echinocytes or spherocytes were seen) but a slight decrease in diameter was detected and RBC started to slightly lose biconcavity. As opposed to previous in vivo studies in mice exposed 2+

to Pb

[1] no additional reagents other than clotrimazole were needed to achieve inhibition of

lead effect in human RBC. In addition, clotrimazole appeared not to have any significant effect on untreated erythrocytes. Lead-induced eryptosis is considered to be ceramide-related, like other mechanisms of RBC death [2]. This data is relevant in the context of sphingolipid signaling and cell death. References [1] Mandal S, Mukherjee S, Chowdhury KD, Sarkar A, Basu K, Paul S, Karmakar D, Chatterjee M, Biswas T, Sadhukhan GC, Sen G. "S-allyl cysteine in combination with clotrimazole downregulates Fas induced apoptotic events in erythrocytes of mice exposed to lead." Biochim Biophys Acta 1820: 9-23 (2012) [2] Montes LR, López DJ, Sot J, Bagatolli LA, Stonehouse MJ, Vasil ML, Wu BX, Hannun YA, Goñi FM, Alonso A “Ceramide-enriched membrane domains in red blood cells and the mechanism of sphingomyelinase-induced hot-cold hemolysis” Biochemistry 47:11222-30 (2008)


Figures

Figure 1: AFM 3D image of control red blood cell (RBC) with typical biconcave morphology

Figure 2: AFM 3D image of spherocyte obtained after 1 hour of lead(II) incubation of RBC


A plant-based nanoplatform for enhancing peptide and protein biological functions Ivonne González, Sol Cuenca, César Cruz, Carmen Mansilla, Flora Sánchez, Fernando Ponz. Centro de Biotecnología y Genómica de Plantas (UPM-INIA). Campus de Montegancedo. Autopista M-40, 28223 Pozuelo de Alarcón, Madrid, España ivonsitag.itesm@gmail.com Viruses can be considered as nano-objects due to their size, monodispersity and symmetry. Plant viruses are produced with a low cost and hereby are presented as a possible biocompatible support for protein immobilization. Turnip mosaic virus (TuMV) is a plant virus included in the genus Potyvirus. The viral particle has a flexuous tubular structure, approximately 720 nm long and 12-15 nm wide. Previous work carried out in our lab showed TuMV suitability for peptide and protein immobilization using chemical conjugation protocols and genetic fusion. Recent advances have allowed the development of virus-like particles (VLPs) from TuMV, based on the CP self-assembling ability. These VLPs are structurally similar to native viruses but lack any genetic material. As a consequence they are not able to infect hosts plants, therefore providing a significant step towards using bio-safe viral derived particles in several applications. VLPs can be exploited as nanoplatforms for the presentation of foreign epitopes and/or targeting molecules. This can be achieved through modification of the VLP coding sequence, such that fusion proteins are assembled into VLPs during de novo synthesis. Using plants as biofactories would definitely raise their production, especially when using systems that increase the expression of proteins. Now if we portray this production on a rod shape virus the possibilities are notably enhanced. This is because the area for peptide display is greater; hence the amount of peptides that fused to the CP is much larger than that in icosahedrical viruses. This nanoplatform is suited for the fusion of several peptides which could be used as diagnostic tools, antibody generation, immunization or biomaterials. This is promising for the biomedicine and nanotechnology fields, confirming that potyviruses can be used as nanoplatforms for epitope fusion. In addition, we validate that plants constitute excellent biofactories for this emerging technology and most importantly, the broad (and expanding) spectrum of possibilities where it could be applied.

References [1] Bendahmane, M., Koo, M., Karrer, E., and Beachy, R. N. Journal of Molecular Biology, 290(1) (1999) 9-20. [2] Canizares, M. C., Lomonossoff, G. P., and Nicholson, L. Expert Review of Vaccines, 4(5), (2005) 687-697. [3] Gleba, Y., Klimyuk, V., and Marillonnet , S. Current Opinions in Biotechnology, 18(2), (2007) 134-141. [4] Kumar, S., Ochoa, W., Singh, P., Hsu, C., Schneemann, A., Manchester, M., Olson, M., and Reddy, V. Virology 388(1), (2009) 185-190. [5] Lico, C., Capuano, F., Renzone, G., Donini, M., Marusic, C., Scaloni, A., Benvenuto, E., and Baschieri, S. Journal of General Virology, 87, (2006) 3103-3112. [6] Sainsbury, F., Liu, L., and Lomonossoff, G. P. Methods of Molecular Biology, 483, (2009) 25-

39. [7] Sainsbury, F., Thuenemann, E. C., and Lomonossoff, G. P. Plant Biotechnology Journal, 7(7) (2009), 682-93.


TEMPERATURE/pH DUAL STIMULI–RESPONSIVE COPOLYMERIC NANOHYDROGELS. SYNTHESIS, CHARACTERIZATION, PROPERTIES AND NANOMEDICINE APPLICATIONS 1

2

1

3

Issa Katime , Aintzane Asumendi , Arturo Álvarez–Bautista , María D. Boyano , Saira 1 2 3 4 Hernández Olmos , Erika Alonso–Tejerina , Teresa G. Granda , María D. Blanco 1 Grupo de Nuevos Materiales y Espectroscopia Supramolecular, Facultad de Ciencia y Tecnología, UPV/EHU. Instituto de Investigación Sanitaria BioCruces. Vizcaya, Spain. Email: issa.katime@ehu.es 2 Departamento de Biología Celular e Histología, Facultad de Medicina y Odontología UPV/EHU 3 Instituto de Investigación Sanitaria BioCruces, Vizcaya, Spain. 4 Departamento de Bioquímica. Facultad de Medicina. Universidad Complutense de Madrid, Spain.

Cancer is a disease caused by a group of cells that grow and multiply themselves uncontrollably independently, locally and remotely invading other tissues. Currently there is an urgent need for the use of new forms of administering therapeutic drugs for its treatment, focusing on the ability of the drug to distinguish tumor cells from the healthy ones.

New methods for the release of drugs have been developed to provide better dosing and pharmacokinetic profile and even the reduction of adverse effects. According to the Royal Spanish Pharmacopoeia, this new forms of modified methods are administrated intravenously but are based on the located release of the active substance, minimizing the dosage in comparison with the methodologies used before.

In this context smart nano–hydrogels seem to be a promising approach taking into account the collapsing and swelling properties of the polymers. This is particularly interesting in the case of hydrogels containing poly(N–isopropylacrylamide), which generate matrices that can exhibit thermally reversible collapse above the lower critical point temperature of the homopolymer (≈ 32 °C) and containing also comonomers which exhibit pH responsive changes as 1–vinyl imidazole, acrylic acid and 2-(diethylamino) ethyl methacrylate.

To avoid post–polymerization modification, functionalized monomers able to respond to pH and temperature changes were polymerized. The synthesized monomers have the capability for coupling with folic acid which is the target molecule. For this reason their polymers can be used as targeted drug delivery systems. Smart polymeric nanoparticles were prepared by direct and inverse microemulsion polymerization of the synthesized monomers. The polymerization reaction was performed in presence of an oil–soluble salt to reduce the dimensions of the micellar diameter. The average particle diameter and the particle size distribution of the nanogels were measured in water, at 25 ºC, by quasielastic light scattering (QLS) showing an 1

average diameter of 33 nm. The nanogels were studied by FTIR–ATR, H NMR, UV–Vis spectroscopy and DSC. The nanoparticles were charged with drugs and their release kinetic was studied.


Moreover, if an appropriate co–suitable monomer is incorporated, these systems could also have a pre–designed response at different values of pH, releasing the drug selectively; this could be achieved by introducing a pH sensitive monomer in the polymeric core such as 1– vinylimidazole (VMDZ) and acrylic acid or 2–(diethylamino) ethyl methacrylate. Another feature of those intelligent materials is their ability to reach a specific target (cancer cells). As the cancer cells over express folate receptors nanohydrogels are usually functionalized with folic acid so as the receptor–ligand complex can be formed in the cell membrane, enabling an endocytosis process mediated by receptor. We present a synthesis for the poly(NIPA–co–VMDZ) and 2– (diethylamino) ethyl methacrylate which detects pH difference making possible the release of the drug at the theoretical temperature of cancer cells.

In this work the synthesis of smart nanoparticles capable of responding to external stimulus (pH and

temperature

variations)

is

reported.

To

avoid

post–polymerization

modification,

functionalized monomers able to respond to pH and temperature changes were polymerized. The synthesized monomers have the capability for coupling with folic acid which is the target molecule. For this reason their polymers can be used as targeted drug delivery systems. These nanoparticles had shown a selective swelling–collapse response to external pH changes. The nanoparticles were charged with drugs and their release kinetic was studied.

References

1. Antonietti M., Bremser W. Macromolecules, 23 (1990) 3796–3805 2. Aguiar A., González–Villegas S., Rabelero M., Mendizábal E., Domínguez J. M., Katime I., Macromolecules, 32(20) (1999) 6767–6771 3. Rabelero M., Zacarias M., Mendizábal E., Puig E., Dominguez J.M., Katime I., Polym. Bull., 38(6) (1997) 695–700. 4. Guerrero–Ramírez L.G., Nuño–Donlucas S.M., Cesteros L.C., Katime I., Mater. Chem. Phys., 112 (2008)1088–1092 5. Blanco M.D., Guerrero S., Benito M., Fernández A., Teijón C., Olmo R., Katime I., Teijón J.M., Polymers, 3(3) (2011)1107–1125 6. Blanco M.D., Guerrero S., Teijón C., Olmo R., Pastrana L., Katime I., Teijón J.M., Polym. Int., 57, 1215–1225 (2008). 7. Guerrero–Ramírez L.G., Nuño–Donlucas S.M., Cesteros L.C., Katime I., J. Phys. Conference Series, 127 (2008)12010. 8. Katime I., Guerrero L.G., Mendizábal E. “Size Matters: Smart copolymeric nanohydrogels: Synthesis and applications”, in Frontiers in Bioscience, E4, 1314–1334 (2012) in “Polymer base nanomaterials for biomedical applications”. P. Taboada and V. Mosquera (Editors).


Molecular characterization of drug nanocarriers based on Plasmon Enhanced Spectroscopies: Fluorescence (SEF) and Raman (SERS) P. Sevilla

1,2,

2

2

2

2

, M. Hernández , E. Corda , J.V. García-Ramos , C. Domingo

1

Facultad de Farmacia, Universidad Complutense de Madrid, 28040 Madrid, Spain. 2 Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain. marga@iem.cfmac.csic.es

Introduction Metallic nanoparticles are ideal materials for developing novel analytical methods, since they have shown excellent optical properties due to excitation of Localized Surface Plasmon (LSP), which result in strong absorption bands and an enhancement of local electromagnetic fields [1]. Such near-field enhancement is profited by molecular spectroscopic techniques such as Raman and fluorescence, consequently improving their corresponding detection sensitivities. Thus, Surface-enhanced Raman Scattering, SERS [2], and Surface-enhanced Fluorescence, SEF [3], have become appreciated highsensitivity label-free detection methods, with imaging capabilities [4]. In fact, interaction of the antitumoral drug emodin with silver nanoparticles has been previously studied in our group [5]. On the other side, metallic nanoparticles are also useful as drug nanocarriers [6]. Here we present our recent developments in applying SEF (and SERS), using silver colloids as plasmonic substrates, to the detection of different drugs: a) the emodin (EM) embedded in porous silicon (PSi), a biodegradable material of interest in drug delivery [7], and b) the NSAIDs indomethacin (IM) and ketorolac (KT) in solution. Experimental methods Silver colloids (50 nm mean diameter silver nanoparticles) were prepared using hydroxylamine hydrochloride as reduction agent [8]. PSi matrices, with mean pore size of 60 nm, were obtained by electrochemical attack of silicon in a solution of HF in ethanol [9]. All fluorescence and Raman experiments were recorded on a Renishaw Raman in Via Microscope system, with laser excitations at 325, 442, 532 y 785 nm. In the case of emodin experiments, atmospheric and vacuum conditions at room temperature were used to infiltrate emodin-silver nanoparticles complexes into PSi matrices. The drug was loaded after adsorption on metal surface, alone, and bound to bovine serum albumin (BSA). Methanol and water were used as solvents. Results While we verified that pristine emodin didn´t penetrate the PSi channels (usually PSi requires a previous functionalization to be able to load drugs), the system emodin-Ag nanoparticles did, as we confirmed through SEF spectra of cross-section of porous silicon layers taken with 1 µm spatial resolution [9]. A maximum fluorescence enhancement factor of 24 was obtained when protein was loaded bound to albumin, and atmospheric conditions of inclusion were used. A better penetration was obtained using methanol as solvent when comparing with water. Complexes of emodin remain loaded for 30 days after preparation without an apparent degradation of the drug, although a decrease in the enhancement factor was observed. Before loading PSi with indomethacin or ketorolac it is necessary to have a deep knowledge of physicochemical and spectroscopic properties of the drugs in solution. As there is a lack of spectroscopic data about IM and KT, we have carried out a deepest investigation of the absorption and fluorescence properties (steady state and time resolved) of IM and KT in different solvents as well as a correlation of them with the corresponding Raman spectra obtained in solution. Additionally, as the drugs delivered orally have to survive encounters with various pHs (2 in stomach and above 8 in duodenum), we have also studied the spectra in the pH range of 1–9, in order to get data about their stability in these conditions because it is essential for a better understanding of the physiological processes involved. Moreover, we have also characterized the corresponding spectra after addition of a silver colloid to the solutions, aiming to find the optimal experimental conditions for getting SERS and SEF spectra of both drugs in solution.


Conclusions SEF (and SERS) could be employed as label-free high sensitivity detection techniques to probe drug delivery and drug release. The joint use of both techniques provides information about the molecular species adsorbed on silver surface at different pHs values. Emodin adsorbed on a silver colloid has been loaded in a PSi silicon matrix without previous surface functionalization.

References [1] S. A. Maier, PLASMONICS; FUNDAMENTALS AND APPLICATIONS, Springer, New York (2007) [2] K.A. Willets and R.P. Van Duyne, Annu. Rev. Phys. Chem., 58 (2007) 267−297. [3] K. Aslan, I. Gryczynski, J. Malicka, E. Matveeva, J.R. Lakowicz and C.D. Geddes, Curr. Opinion in Biotechnology, 16 (2005) 55-62. [4] C.D. Geddes, H. Cao, I. Gryczynski, Z. Gryczynski, J. Fang and J.R. Lakowicz, J. Phys. Chem. A 107 (2003) 3443–3449. [5] P. Sevilla, F. Garcia-Blanco, J.V. Garcia-Ramos an S. Sanchez-Cortes, Phys. Chem. Chem. Phys. 11 (2009) 8342-8348; P. Sevilla, R. De-Llanos, C. Domingo, S. Sanchez-Cortes and J.V. GarciaRamos, "SERS plus MEF of the anti tumoral drug emodin adsorbed on silver nanoparticles" in: PLASMONICS IN BIOLOGY AND MEDICINE VII, T. VoDinh, J.R. Lakowicz, eds., SPIE, Bellingham, (2010), 757714.; R. De-Llanos, S. Sanchez-Cortes, C. Domingo, J.V. Garcia-Ramos and P. Sevilla, J. Phys. Chem. C 115 (2011) 12419-12429. [6] S. Singh, J. Nanosci. Nanotechnol, 10 (2010) 7906–7918. [7] J. Salonen, A.M. Kaukonen, J. Hirvonen, V-P. Lehto: J. Pharm. Sci., 97 (2008) 632–653. [8] N. Leopold, B. Lendl, J. Phys. Chem. B, 107 (2003) 5723–5727. [9] M. Hernandez, G. Recio, R. Martin-Palma, J. Garcia-Ramos, C. Domingo and P. Sevilla, Nanoscale Res. Lett. 7 (2012) 364.

This work has been financially supported by Comunidad de Madrid (MICROSERES II S2009TIC-1476), MINECO (FIS2010-15405) and UCM (Research Group 950247). G. Recio and R.J. Martín-Palma (UAM, Madrid) are gratefully acknowledged by preparation of the porous silicon samples.


THE DEVELOPMENT OF MAGNETIC SUBSTRATES WITH DETERMINED 3D GEOMETRY OF MAGNETIC FIELD FOR THE BIOTECHNOLOGY APPLICATIONS T.A.Ignatyeva1, V.N.Voevodin1, P.A.Kutsenko1, V.V.Kalynovskyi1, Y.I.Dzhezherya2, V.О.Golub2, V.V.Kiroshka3 1 National Scientific Center “Kharkov Institute of Physics and Technology, 1 Akademicheskaya str. 61108 Kharkov, Ukraine 2 Institute of Magnetism NASU and MESYSU, 36-B Vernadsky blvd., 03142 Kiev, Ukraine 3 Institute for Problems of Cryobiology and Cryomedicine NASU, Pereyaslovkaya str., 61015 Kharkov, Ukraine taignatieva@mail.ru A future progress in science and technology is connected with the implementations of nanomaterials. Nanotechnology will allow the creation of new materials and devices with a vast range of applications, such as in electronics, medicine, biomaterials and energy production. One of the most promising applications of the nanotechnology is tissue engineering, i.e. repair or replacement of portions of or whole tissues. The development of this direction will open new opportunities for the creation of effective biomedicine techniques for neogenesis and therapy of a bunch of severe metabolic diseases. On of the main tasks here is to create favorable conditions for 3d tissue growing for substitution of damages or pathologies. The goal of tissue engineering is a construction and growing of live and functional tissues and organs outside an organism for a following transplantation to a patient. Polymer biocompatible materials with pores of definite sizes are widely investigated now as materials which could provide spatial cells growth and formation of 3d tissue structure. In this case the tissue could not only replace a damaged area but fulfill biological (metabolic) functions. It should be noted that usual implants produced from inert materials can improve only physical and mechanical defects of damaged tissues. New approaches based on tissue engineering should be developed to improve the techniques of reconstructive medicine to create bioimplants with characteristics of live tissues: - regeneration ability; - blood supply maintenance ability; - ability to change structure and functions in response to environmental factors. Our goal is the manipulation of spatial cell growth using magnetic fields and this work is devoted to the development of magnetic field concentrators (substrates) that could produce high gradient magnetic fields of required configuration over large area. The image of proposed substrate-magnetic conductor obtained with optical microscope is shown in Fig.1. The magnetic field is produced by permanent magnet while the substrate determines magnetic field lines distribution.

а

b

c

d

Figure.1 Optical image of magnetic conductor-substrate (a). The distance between centers of squares is 1.65 mm. The side of square is 0.35-0.40 mm. A step height is 20 μm. (b) View of a dot. (c) Focus on the top of the step. (d) Focus on bottom of the step. The distribution of magnetic fields formed over such substrates can be understood from a simple theoretical model [1]. A fragment of periodical structure which is quite simple to be produced technologically and that can produce high gradient magnetic fields is shown in Fig. 2. The system is a 2d array of magnetic rods. The interrod distance is a, the rod height and width are z0 and d correspondingly. The saturation magnetization of the dots is Ms. The rods are supposed to be saturated along z-direction.


a

b

Figure.2. Model magnetic system (a) and the distribution of z-component of magnetic fields as a function of x for different heights (b). To calculate the distribution of magnetic fields the approach of effective magnetic charges was used. If ferromagnetic rods have a small base radius the top of the rod can be considered as a point 2 magnetic charge qM = M sπ d 4 and the bottom of the rod as − qM . In this case the magnetic potential takes the form

ψ ( r ) = qM

 ∑ ∑ ( ( x − a ⋅ n ) + ( y − a ⋅ m ) ∞

2

2

n =−∞ m =−∞

+ z2

) − ( ( x − a ⋅ n) 12

2

+ ( y − a ⋅ m ) + ( z + z0 2

)

)

2 12

  

(1)

If z >> z0

ψ ( r) =

z ⋅ qM z0

∑∑

n =−∞ m =−∞

( ( x − a ⋅ n)

2

+ ( y − a ⋅ m) + z2 2

)

32

(2)

Here qM z 0 is just the magnetic moment of the dot μ. Thus only one scale parameter (lattice period) remains in the system. Substituting ξ = x a, η = y a, ζ = z a the expression (2) can be rewritten as

ψ ( r) =

µ a2

ζ

∑ ∑

n =−∞ m =−∞

( ( ξ − n)

2

+ ( η − m) + ζ 2 2

)

32

(3)

This expression allows to obtain the magnetic field in any point of the space where z >> z0 . The field is inhomogeneous and high gradient only for heights below z ~ a see Fig.2. So if the lattice period is 1 mm the field will be inhomogeneous only if the height above the substrate does not exceed several millimeters. To increase the heights of the gradient magnetic field created by such substrate the period of modulation of the magnetization inside the substrate should be optimized. The heights will increase with the modulation period but this will decrease gradients of the field. So we need to provide additional steos to increase the magnetic field inhomogeneity. The shape of the magnetic elements should be more complicated (bars, stars, etc.) like in substrates proposed here. [1] L.D. Landau & E.M. Lifshitz. The Classical Theory of Fields (Volume 2 of A Course of Theoretical Physics ) Pergamon Press 1971.


Diffusion of water molecules in CNT’s functionalized with aminopyrene molecules 1

Isabel Lado Touriño, 1Arisbel Cerpa Naranjo, 1Piedad Ros Viñegla, 1Mª José Rodríguez Portela 2,3 Viviana Negri, 3Sebastián Cerdán and 2Paloma Ballesteros 1

Universidad Europea de Madrid, C) Tajo s/n, 28670 Villaviciosa de Odón, Spain misabel.lado@uem.es 2 Laboratory of Organic Synthesis and Molecular Imaging by Magnetic Resonance, Faculty of Sciences, UNED, 28040-Madrid, Spain, 3 LIERM, Institute of Biomedical Research “Alberto Sols”, CSIC, 28029-Madrid, Spain,

Abstract Magnetic Resonance Imaging (MRI) is currently one the most useful methods in clinical diagnosis. Its effectiveness may be improved by the design of new MR sequences highlighting the physiopathological properties of tissues and through the development of new Contrast Agents (CAs) increasing the quality, resolution and specificity of the MR images.1 Diffusion tensor Imaging (DTI) is a recent methodology that allows the visualization of the white matter tracts underlying cerebral morphology and architecture. This methodology allows to study white matter diseases and has proven useful in the diagnosis of many neurological disorders, including demielinating diseases and ischemic and oncological processes. However, at present, there are not appropriate contrast agents to improve specificity and resolution of the DTI approach. We have previously shown that paramagnetic carbon nanotubes are able to perturb the diffusion of surrounding water molecules in an anisotropic manner, with larger effects in the longitudinal than in the transversal directions, constituting at present the first contrast agent for DTI.2 However, the approach has remained limited by the reduced solubility of the nanotubes and the lack of sufficiently robust models to describe water diffusion in these systems. In this work we report recent progress in increasing solubility and paramagnetic character of CNTs obtained using pyrene adducts stabilized by−π stacking and Gd(III) derivatives of MWNTs. We focus then in the diffusional behavior of water molecules in the presence of the aminopyrene CNT adduct, to characterize the influence of various parameters such as length, diameter and concentration of carbon nanotubes and aminopyrene molecules. Our modeling study shows that the presence of CNT’s modifies the diffusional behavior of water relative to bulk behavior and that diffusion of water molecules inside CNT’s is slower than in the bulk solvent. Results on the distribution of water molecules in the interior of CNT’s are also reported. References [1] Pacheco-Torres,J., Calle,D., Lizarbe, B.,Negri,V., Ubide,C.,Fayos, R., Lopez-Larrubia,P., Ballesteros,P. and Cerdan,S. Curr. Top. Med. Chem. (2011) 11: 115-130. [1] Meerbach, A. E.; Toth, E. Eds. In the chemistry of contrast agents in medical magnetic resonance imaging. John Wiley & Sons, Ltd., Chichester, (2001). (2) Negri, V., Cerpa, A.; López-Larrubia, P.; Nieto-Charques, L.; Cerdán, S.; Ballesteros, P., Angewandte Chemie Int. Ed. (2010) 49: 1813-1815.


Figures

Figure 1. Model system used for the simulation of a CNT and two aminopyrene molecules in water.

Figure 2. A snapshot from the simulation showing the structure of the hydrogen-bonded water chain inside the nanotube


Physicochemical characterization of nanometric materials by A4F-MALLS-ICPMS and DLS: industrial and environnemental applications. 1

1

1

Mathieu MENTA , Christine GLEYZES , Damien Plaa , J茅r么me FRAYRET

2

1

2

Ultra Traces Analyses Aquitaine, 2 avenue Pierre Angot 64053 Cedex 9, Pau, France Laboratory of Bioinorganic Analytical and Environmental Chemistry, 2 avenue Pierre Angot 64053 Cedex 9, Pau, France mathieu.menta@univ-pau.fr ; christine.gleyzes@univ-pau.fr ; damien.plaa@univ-pau.fr ; jerome.frayret@univ-pau.fr

Abstract Nanomaterials (NM) open huge prospects for innovation in different fields such as medicine, electronics, cosmetics and materials [1]. However, their uses raise questions about possible risks to the environment and humans [2]. The development of suitable protocols for the physicochemical characterization (size distribution, shape and chemical composition) of such materials is a fundamental issue for coming years [3]. To meet the needs of various industrial producing or using NM, UT2A has developed new analytical approaches dedicated to nanometrology. According to the needs expressed by industry, two approaches were considered. The first one is focused on the determination of the size distribution of nano-scale particles using Dynamic Light Scattering detector (DLS) and a splitting system (by size and weight) such as Asymmetric Flow Field Flow Fractionation hyphenated with a Multi Angle Laser Light Scattering detector (A4F-MALLS). The second approach is based on a comprehensive physicochemical characterization made by the combination of A4F-MALLS with an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The first part of the work has consisted in the size control of Metallic NanoParticles (MNP) and Carbon NanoTubes (NTC) respectively used in cosmetics and computer science (Figure 1). The main difficulty resided in the sample preparation protocol. To do so, the nature and concentration of the surfactant and the mechanical means were considered. Subsequently, the work was focused on the optimization of industrial processes. The development of a new method for monitoring aeronautical degreasing baths containing surfactant micelles (nano-scale entities) by DLS improved their managements and significantly reduced costs and the volume of effluents. An industrial process of cheese manufacturing has also been optimized by evaluating the influences of the temperature and the homogenization step on the final cheese texture by analyzing the size distribution of milk creams. The second part of the work was focused on the development of A4F-MALLS-ICP/MS for the physicochemical characterization of NM in sunscreens (Figure 2). The protocol of extraction of NM (solvent, centrifugation, dispersion, etc.) and the optimization of the separation step were implemented (mobile phase composition, fractionation step, etc.). The same hyphenated system was also used to evaluate the physicochemical characteristics of environmental colloids and their interactions with various metallic pollutants (Figure 3). The analysis of leachates have demonstrated that most of metals (Cu, Zn, Ni, As, Cd) investigated were dissolved instead between 20 and 90% of Al, Fe and Pb were associated with particles from 50 to 350 nm.

References [1] B.F. Da Silva, S. P茅rez, P. Gardinalli, R.K. Singhal, A.A. Modesto, D. Barcel贸, Trends in Analytical Chemistry, 30(8) (2011) pages 1327-1336. [2] V.L. Colvin, Nature Biotechnology 21 (2003) pages 1166-1170. [3] H. Weinberg, A. Galyean, M. Leopold, Trends in Analytical Chemistry, 30(1) (2011) pages 72-83.


Figures

A

B

Figure 1. Characterization of the size distribution of sunscreens by DLS (A) and carbon nanotubes by A4F-MALLS (B).

Figure 2. Characterization of titanium nanoparticules in sunscreens by A4F-MALLS-ICPMS.

A

B

Figure 3. Characterization of environmental colloids in leachates (A, B) by A4F-UV-MALLS-ICPMS.


Improved Therapy of Colorectal Cancer with Camptothecin-Loaded Silica Nanoparticles: A Preclinical Study 1

1

2

2

1

C. Muniesa, P. Botella , I. Abasolo, Y. Fernández, M. Quesada, S. Schwartz Jr. 1

2

Instituto de Tecnología Química (UPV-CSIC), Av. de los Naranjos s/n, Valencia, Spain 2 Hospital Universitari Vall d’Hebron, Passeig Vall d’Hebron 119, Barcelona, Spain carmula@itq.upv.es

Abstract Introduction: Although silica nanoparticles (MSN) have found application for the delivery and controlled release of small therapeutic molecules [1-3], very few studies report on the performance of silica-based nanodrugs at the preclinical stage [4,5]. Here, we demonstrate that surface-modified silica nanoparticles loaded with camptothecin (SNP-CPT) show high therapeutic efficacy and biocompatibility in human colorectal cancer xenografts. Methods: Amorphous silica nanoparticles (10 nm average diameter) with the drug linked by ester bond at the 20-OH position were prepared as reported [6]. A human subcutaneous colorectal mouse model was used for the tolerability and efficacy studies. For this purpose, HT-29.Fluc cells were subcutaneously injected on the rear right flank of mice (female athymic nude mice, Harlan) and tumor growth was monitored twice a week for 22 days by conventional caliper measurements. During this time, tumor-bearing mice were treated intravenously with 0.8 mg CPT equivalent/kg twice a week. The toxicity of the compounds was determined by monitoring the animal’s body weight (T/C ratio), eating and physical activity results [4,7]. Results and discussion: The treatment with naked CPT induced dose-dependent severe toxicities such as pain, hematuria, necrosis and partial loss of the tail. In contrast, the administration of SNP-CPT colloids did not induce any damage in the animals. The nanodrug accumulated preferentially in tumor by EPR effect [8], inducing a more effective tumor growth delay than naked CPT (Fig. 1). This may be due to the slow release of the drug from SNP-CPT in the tumor tissue, as the acidification within the lysosomes may stabilize the ester linkage, providing a slow release mechanism for the active drug that allows for a long-term therapeutic effect [9]. Conclusion: Colloids of silica constitute a novel drug delivery system for CPT that imposes improved tumor growth inhibition than naked drug and shows no toxicity, thus widening the therapeutic window of current alkaloid anticancer treatments. References [1] J.M. Rosenholm, C. Sahlgren, M. Linden, M., Nanoscale 2 (2010), 1870. [2] I.I. Slowing, J.L. Vivero-Escoto, C.W. Wu, V.S. Lin, Adv. Drug. Deliv. Rev. 60 (2008) 1278. [3] J. Lu, M. Liong, J. I. Zink, F. Tamanoi, Small, 3 (2007) 1341. [4] J. Lu, M. Liong, Z. Li, J.I. Zink, F. Tamanoi, Small, 6 (2010) 1794. [5] J. Shen, Q. He, Y. Gao, J. Shi, Y. Li, Nanoscale, 3 (2011) 4314. [6] P. Botella, I. Abasolo, Y. Fernández, C. Muniesa, S. Miranda, M. Quesada, J. Ruiz, S. Schwartz, Jr., A. Corma, J. Controlled Release, 156 (2011) 246. [7] C. Ahowesso, E. Piccolo, X.M. Li, S. Dulong, V. Hossard, R. La Sorda, E. Filipski, N. Tinari, F. Delaunay, S. Iacobelli, F. Levi, Toxicol. Lett. 192 (2010) 395. [8] H. Maeda, J. Wu, T. Sawa, Y. Matsumura, K. Hori, J. Control. Release, 65 (2000) 271. [9] T. Schluep, J. Cheng, K.T. Khin, M.E. Davis, Cancer Chemother. Pharmacol. 57 (2006) 654.


Figures

a

b 1200

PBS CPT SNP-CPT

Tumor Volume

(mm3) (Mean SEM)

SNP-CPT 3.0 2.5

800

2.0

600

1.5

400

1.0

ď&#x201A;´10 9 Intensity BLI (ph/s)

1000

Control

0.5

200 0 1

3

5

7

9

11 13 15 17 19 21 23

Time (days)

Fig. 1 a) Growth inhibition curves of the localized subcutaneous HT-29.Fluc colorectal cancer tumors in athymic nude mice treated with CPT or SNP-CPT. For comparison, a control administrated with PBS is also shown. Vertical arrows indicate points of drug injection; b) In vivo evolution of tumor HT-29.Fluc in athymic female mice (day 22 of treatment) by bioluminescence image. Left: the control was administered saline solution. Right: mouse received two injections per week of a SNP-CPT suspension in saline solution, corresponding to a 0.8 mg CPT/kg dose. Significant tumor recession and necrosis in the SNP-CPT treated mouse can be observed.


Ingestion and reproductive effects of gold nanoparticles in Blattella germanica. T. Smalla, M.A. Ochoa-Zapatera*, F.M. Romerob, A. Riberab, G. Gallelloc, A. Torreblancaa, M.D. Garceráa. a

Departamento de Biología Funcional y Antropología Física, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain. b Instituto de Ciencia Molecular, Universitat de València, Catedrático José Beltrán, 2. 46980, Paterna, Valencia, Spain. c Departamento de Química Analítica, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain. * ozama@alumni.uv.es

Abstract Introduction: Many biomedical, commercial and industrial advances have on their agenda the use of nanoparticles of different chemical elements, shapes and grade of aggregation due to their multiple applications and novel properties. All this progress must go hand in hand with studies verifying that the use of these nanoparticles is not harmful to biological compounds and the environment, while helping to establish threshold values for their application. The objective of this study is to investigate the possible toxic effects of nanoparticles that could be used as insecticide carriers in order to determine its hazard over an organism as Blatella germanica. . Methodology: The effects of daily administration through the diet of gold nanoparticles (AuNPs) on the reproduction of Blattella germanica were studied. Nanoparticles were synthesized following the method described by Bastús et al. [1] and characterized by UV-VIS and Transition Electron Microscopy (TEM) (figure 1). Fifteen newly molted females from a laboratory reared population were feed with a solution of AuNPs (diameter range between 22 and 25 nm) in sodium citrate mixed with crushed rodent chow. Harborage and water were provided ad libitum. Food was weighted daily to estimate consumption. Females were inspected daily for ootheca formation and for monitoring development, releasing and hatching times of oothecas. During the experiment females were in contact with males only until the formation of the first ootheca since it has been shown that a single mating is sufficient to fulfill the reproductive life of a female [2]. All studied parameters were monitored until the hatching of the third ootheca of each female cockroach and mortality rates were recorded. At the end of the study, which was performed two times, all insects were frozen and gold content was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, injection of nanoparticles solution, spray exposure by a Potter spray tower and the tarsal contact test bioassays were carried out for the study of the AuNPs toxicity [3]. Each bioassay was replicated three times using 5 to 10 adults of the same laboratory-reared population, aged 1 day; mortality rates were scored 24 h, 48 h and 72 h post-treatment. Results: As described in bibliography [2, 4], food consumption increased previously, and decreased following, the ootheca formation. But in our case, females treated with AuNPs showed a significantly higher food consumption rate than control ones (3,69 mg and 1,28 mg per insect and day, respectively). No Au content was detected in control individuals while treated insects had a mean concentration of this element of 12,70 μg per mg of insect. These results point to the existence of some degree of accumulation of AuNPs in the body of the insects; however, the difference between the amount of gold measured and the one estimated from the amount of food ingested suggests that Au NPs were mostly excreted. Regarding the ootheca formation parameter, treated females showed a significant delayed onset of the first ootheca (figure 2). Moreover, only one control female released her first ootheca empty while in the case of treated cockroaches, two females released the first ootheca empty, three the second one and five the third one. Generally, Blattella germanica ootheca occasionally breaks off prematurely in the case of virgin females with sterile eggs [5]. Similarly, ootheca can be ruled out by females when they have been exposed to insecticides [6]. As suggested by Pompa et al. [7], AuNPs may act as catalysts accelerating the oxidative processes and the production of reactive oxygen species, affecting fertility and reproduction. Despite these alterations, both development and release times of all ootheca were not significantly different between the control group and the group of treated insects (figure 3). Neither of the bioassays performed for the assessment of AuNPS toxicity showed significant mortality rates.


Acknowledgements: This work has been supported by grant AGL2010-21555 from the Ministerio de Economía y Competitividad.

References [1] N.G. Bastús, J. Comenge, V. Puntes, Langmuir, 27 (2001) 11098-11105. [2] D. Cochran, Entomologia Experimentalist et Applicata, 34 (1983) 51-57. [3] WHO, Technical Report Series, Annex 12, 443 (1970) 130-133. [4] L. How-Jing and W. Yen-Li, Physiological Entomology, 19 (1994) 39-45. [5] G. Barson and N. Renn, Entomologia Experimentalist et Applicata, 34 (1983) 179-185. [6] B.M. Parker and F.L. Campbell, Journal of Economic Entomology, 4 (1940) 610-614. [7] P.P. Pompa, G. Vecchio, A. Galeone, V. Brunetti, S. Sabella, G. Maisorano, A. Falqui, G. Bertoni and R. Cingolani, Nano Research 4 (2011) 405-413.

Figures

Figure 1.- TEM characterization (left) and frequency of size distribution (right) of gold citrate-capped (scale bar 20 nm) NPs. Average size of 21.8± 3 nm was obtained in these AuNPs.

Figure 2.- Average number of days (±SD) until formation of each ootheca. A, control females; B, AuNPs treated females. 1st, first ootheca; 2nd, second ootheca; 3rd, third ootheca.

Figure 3.- Recorded mean time (±SD) in days that females carried each ootheca from their formation to their release. A, control females; B, AuNPs treated females. 1st, first nd rd ootheca; 2 , second ootheca; 3 , third ootheca.


Controlled release of calcium and phosphate ions from nanogels for in situ mineralization in bone tissue engineering Beatriz Olalde1, Virginia Saez-Martinez1, Iratxe Paz2, Fabrice Morin1 1

Biomaterials Group. Health Division. TECNALIA. CIBER of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN). Pº Mikeletegui 2, 20009 San Sebastian, Spain 2 iLine Microsystems S.L., Pº Mikeletegui 69, 20009 San Sebastian, Spain beatriz.olalde@tecnalia.com

Abstract Introduction: Biological apatites, the major inorganic component of bone mineral, differ from pure hydroxyapatite (HA) in stoichiometry, composition, crystallinity and other physical and mechanical properties that explain their special behaviour in bone remodelling cycles. Simulated or synthetic body fluids (SBF) are prepared in accordance with the chemical analysis of human body fluid. They are metastable buffered solutions supersaturated towards apatite crystals. When supersaturation degree increases (because of the addition of calcium and phosphate salts), mineralization is induced. Once apatite is nucleated, it can grow spontaneously incorporating ions from the SBF (Na+, Mg2+, CO2−3, etc.) into the structure (so differing from the formula Ca10(PO4)6(OH)2 and 1.67 of Ca/P molar ratio of synthetic ones) and such precipitation is similar to biological mineralization [1]. The term nanogel refers to spherical, nanometric, crosslinked polymer matrix that forms colloidally stable dispersions. Due to their small sizes and high surface-volume ratio, they have fast swelling– deswelling properties [2]. They can be charged with drugs and used as controlled release systems [3,4]. Hydroxyapatite precursor salts (calcium chloride and sodium hydrogen phosphate) can be encapsulated into nanogels to the aim of controlling the hydroxyapatite reaction kinetics. Moreover, nanogels could act as nucleation sites of hydroxyapatite. In this work advantages from the precipitation in SBF and from nanometric hydrogel properties have been combined. When heated to physiologic temperature, above the lower critical solution temperature (LCST) of the poly(N-Isopropylacrylamide-co-acrilic acid) nanogels, both Ca and P ions-loaded nanogels become hydrophobic and release their contents into the SBF solution, where the ions react to form hydroxyapatite mineral. Materials and methods:

Poly(NIPAAm-co-AA) nanogels were synthesized by precipitation radical polymerization in water as previously described [5]. After dialysis and freeze-drying nanometric hydrogels of sizes close to 100nm were obtained. Nanogels were dispersed in highly concentrated aqueous solutions of CaCl2 and Na2HPO4 and after several hours they were recovered by ultrafiltration and freeze-drying. Then, the SBF solution was prepared and the load and controlled release of sodium and phosphate ions was measured. It is known that a Ca/P molar ratio of 1.80 added to SBF guaranties a good biomimetic hydroxyapatite, for this reason, it is necessary to control the behaviour of nanogels in the presence of these ions. Different concentrations of salts and nanogels were used to study the load of the salts into the nanogels (data not shown). The amount of salt loaded into the nanogels was characterized by ICP-AES (Inductively coupled plasma atomic emission spectroscopy, axial, model VISTA-MPX from VARIAN). For the study of the controlled release, loaded nanogels were introduced in dialysis bags with deionized water at 37ºC instead of SBF in order to avoid any precipitation and to determine the Ca or Pi released without the influence of any other salt. The controlled release of Ca or Pi was analyzed at different time points by ICP. For the synthesis of biomimetic hydroxyapatite powders in SBF, both Ca-loaded (1000 mg/ml; 400:3) and Pi-loaded nanogels (90 mg/ml; 12:1), in a ratio of 2:1, were placed in SBF solution for five days at 37ºC. Powders were recovered by centrifugation, washed and dried, and characterized by XRD (D8Advance, Bruker), FTIR spectroscopy and ICP-AES. Results and discussion:

Results demonstrated that the higher the amount of salt in the solution, the bigger amount the nanogels can load, but this loaded amount does not depend on the amount of nanogels. It could be due to electrostatic interactions that only let the nanogels load with salt until a limit, when the limit is reached, no more nanogels absorb salt. Figure 1 shows the accumulated concentration of Ca or Pi released from the nanogels to water along the time. The release almost reached equilibrium at the fourth day. Concentration of Ca or Pi released depends on the amount of loaded nanogels and initial solution concentration used for the load. The


bigger the amount of loaded nanogels, the larger the amount of salt released. Ca/P molar ratios between the Ca and Pi released were estimated from the curves and, as the ideal Ca/P molar ratio to form a biomimetic hydroxyapatite in SBF must be close to 1.80, the combined release from 100 mg of Ca-nanogel and 200 mg of Pi-nanogel was selected for the study of the hydroxyapatite synthesis. XRD spectra of the hydroxyapatite powders recovered after five days incubation of salt-loaded nanogels in SBF solution had got peaks that corresponded to the standard for stoichiometric HA (International Centre of Diffraction Data (ICDD), JCPDS 09-0432) confirming the apatitic nature of the sample. Figure 2 shows FTIR spectra of the powders obtained. The broad band beyond 3000 cm−1 corresponds to the OH groups. The little band at 1650 cm−1 corresponds to adsorbed water. Phosphate groups are seen in the region between 550 and 600 cm−1 and the strong band close to 1000 cm−1. Carbonate vibration bands are observed at 1400–1550 cm−1 confirming the carbonate apatite nature. The percentage of elements found in the sample determined by ICP-AES ( %Na 0.37, %K 0.15, %Mg 0.32, %S 0.04) confirmed the substitutional inclusion of different amounts of ions from the SBF solution in the apatitic structure as in natural hard tissues. Conclusions

Poly(NIPAAm-co-AA) nanogels were capable to charge calcium and phosphate ions and provide a controlled release of them for several days. The released amount and kinetics depends on the initial salt concentration and nanogel/salt ratio, which can be fixed depending on the final result we want to obtain. The approach proposes a method to use the nanogels as controlled release systems and nucleation agents for the in situ precipitation of biomimetic hydroxyapatite from scaffolds. References [1] M. Bohner and J. Lemaitre, Biomaterials, 30 (2009), 2175 [2] D. Huo, Y. Li, Q. Qian, and T. K. Obayashi, Coll. Surf.B., 50 (2006), 36 [3] S. V. Vinogradov, Curr. Pharm. Des., (2006), 4703 [4] M. Hamidi, A. Azadi, and P. Rafiei, Adv. Drug Deliver. Rev. 60 (2008), 1638 [5] V. Saez-Martinez, B. Olalde, M. J. Juan, M. J. Jurado, N. Garagorri, and I. Obieta, J. Nanosci. Nanotechnol. 10 (2010), 2826 Figures

Figure 1. Concentration of the released Ca and Pi in water from nanogels at 37 ºC. (S) 60 mg of Cananogel (1000 mg/ml; 400:3), (♦) 40 mg of Ca-nanogel (1000 mg/ml; 400:3) and (ƒ) 100 mg of Pinanogel (90 mg/ml; 12:1).

Figure 2. FTIR spectra of the biomimetic hydroxyapatite powder obtained.


Polyethylene glycol iron oxide nanoparticles with fluorescent properties a

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Nagore Pérez, Virginia Martinez-Martinez, Matilde Rodriguez, and José Luis Vilas

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Laboratorio de Química Macromolecular (Labquimac), Dpto. Química-Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), Apdo. 644 48080 Bilbao (Spain) b Dpto. Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV/EHU), Apdo. 644, 48080 Bilbao (Spain) c BcMaterials, Basque Center for Materials, Applications and Nanostructures. Ibaizabal Bidea, Ed 500 48160 Derio (Spain) nagore.perez@ehu.es Iron oxide nanoparticles, due to their magnetic properties, can be used as magnetic resonance imaging agents in diagnostic, as heat mediators in hyperthermia treatments, and additionally as magnetic guidance in drug delivery applications. Magnetite (Fe3O4) or its oxidized form maghemite (γ-Fe2O3) are the most commonly employed in biomedical applications since their biocompatibility has been proven[1]. Fluorescent magnetic nanoparticles are formed by a magnetic core coated with an inorganic compound or organic polymer with a bound or embedded fluorophore. The preparation of fluorescent magnetic nanoparticles is, however, challenging. A specific difficulty in the preparation of fluorescent magnetic nanoparticles is the risk of quenching of the fluorophore on the particle surface by the magnetic core. This problem has been solved by coating the magnetic core with a stable isolating shell prior to the introduction of the fluorescent molecule or by attaching an appropriate spacer to the fluorophore.[2] The shell has to be biocompatible and non-immunogenic, preventing the agglomeration of the particles and at the same time minimizing non-specific interactions with proteins, cells and other components of biological media. In this work, polymer coated iron oxide nanoparticles has been synthesized. The role of the polymer coating is twofold: on one hand it prevents the iron from oxidizing and on the other hand it allows the functionalization of the particles and minimizes the direct exposure of the iron nanoparticles surfaces to the biological environment. The polymer coated iron nanoparticles have been synthesized by a microemulsion method in two steps [3]. We have synthesized iron oxide nanoparticles coated by PEG [4,5]. The surface modified nanoparticles are expected to be more biocompatible: non-immunogenic, non antigenic and protein resistant, because PEG has uncharged hydrophilic residues and high surface mobility. The aim is to modify this coating in order to allow the subsequent functionalization of the nanoparticles (mPEG-NH2) [6]. The most studied surface modification of the iron oxide nanoparticles has been their functionalization with different dyes so that the resulting nanoparticles can be detected by both magnetic and fluorescent techniques. Amine-reactive N-hydroxysuccinimidyl ester of Alexa Fluor 660 dye has been conjugated to the nanoparticle surface. This dye produces bright far red fluorescence emission with a peak at 690 nm. In this study, preparation, modification and functionalization of PEG coated iron oxide nanoparticles is reported. We have been able to synthesize high susceptibility iron nanoparticles of sizes between 10-15 nm coated by a polymer.


References [1] Qiao R.R, Yang C.H, Gao M.Y, J.Mater Chem 19 (2009) 6274. [2] Corr S.A, Rakovich Y.P, Gun’Ko Y.K, Nanoscale Res Lett 3 (2008) 87. [3] Zhou W.L, Carpenter E.E, Lin J, Kumbhar A, Sims J, O`Connor C.J, Eur. Phys. J. D 16 (2001) 289. [4] Skumiel A, Józefczak A, Hornowski T, J. Phys. Conference Series 149 (2009) 01211. [5] Yu W.W, Chang E, Falkner J.C, Zhang J, Al-Somali A.M, Sayes C.M, Johns J. Drezek R, Colvin V.L, J. Am. Chem. Soc. 129 (2007) 2871 [6] Harris J.M, Struck E.C, Case M.G, Paley M.S, Yalpani M, Van Alstine J.M, Brooks D.E, J. Polymer. Sci. Polymer Chem 22 (1984) 341 Figures 60 300 K 5K

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Toxicity, uptake and gene expression studies of nanoliposomes used as vaccine delivery systems in aquaculture Àngels Ruyra1,2, Mary Cano2, Simon MacKenzie1, Nerea Roher1, Daniel Maspoch1,3 1

Institut de Biotecnologia i Biomedicina (IBB), Esfera UAB, 08193 Bellaterra, Spain. 2CIN2 (ICN-CSIC), Catalan Institute of Nanotechnology, Esfera UAB, 08193 Bellaterra, Spain. ³Institució Catalana de Recerca i Estudis Avançats (ICREA), 08100 Barcelona, Spain Angels.Ruyra@campus.uab.cat, daniel.maspoch@icn.cat

      Intensive aquaculture often involves high pathogenic burdens in farms that can provoke disease outbreaks accounting for immense economic losses, being the development of protective/vaccination strategies a priority research area for aquaculture industry [1]. Although there are a number of commercial finfish vaccines, the initial expectations have not been fulfilled because the achieved protection levels are usually low, particularly for viral vaccines. In this field, nanotechnology, and more specifically, the use of nanocarriers could help to increase the fish immunisation levels by improving delivery of vaccines and other bioactive agents to specific immune actors (e.g. the innate pathogen receptors (PRRs) located on antigen-presenting cells (APCs) [2]). Furthermore, nanocarriers can also be useful for a proper administration of the adequate doses in order to not over stimulate the immune system, thus avoiding the presence of unwanted side effects. This work presents the development and use of small unilamellar nanoliposomes encapsulating a cocktail of immunological relevant molecules as new carriers to stimulate the fish innate immune response, protecting them against a pathogenic challenge. The selected immunological relevant molecules are the bacterial lipopolysaccharide (LPS) from E. coli and the synthetic analogue of dsRNA virus, polyinosinic:polycytidylic acid (poly (I:C)). Because of this selection, it is expected that this liposomal LPS-poly(I:C) cocktail may be used as non-specific vaccine nanocarrier in different fish species in a near future [3]. Liposomes encapsulating both immunostimulants are prepared by thin film hydratation method using the DLPC:Cholesterol:Cholesteryl:PEG lipid mixture. Through this methodology can be synthesized highly homogeneous small unilamellar vesicles (Figure 1A) with an average particle size of 125.8 nm, which entrap both LPS and poly (I:C) with loading efficiencies of 22.3 % and 99.6 %, respectively. Liposomal formulation showing a positive surface charge (+1.37 mV) is ideal for encapsulating both LPS and poly (I:C). The attractive interaction between the negative charge of immunostimulants and the positive surface charge of liposomes results in the near-perfect conditions to achieve the highest encapsulation efficiencies. The occurrence of these attractive interactions is corroborated by coencapsulating fluorescent labeled-LPS and poly (I:C) into liposomes. Confocal microscope images of liposomes demonstrate that both LPS and poly (I:C) are incorporated into their cationic lipid bilayer.


a

20 μm Figure 1. (a) Cryo-TEM image of DLPC:Cholesterol:Cholesteryl:PEG liposomes extruded through a 200 nm pore size membrane. (b) Confocal microscopy image of fluorescently tagged liposomes endocyted by zebrafish hepatocyte cells (3D reconstruction). Cells were incubated 30 min. with liposomes containing DHPE-Fluorescein (green).

We show that this liposomal nanocarrier presents low toxicity not only in vitro using three different cellular models but also in vivo using zebrafish embryos and larvae. Using fluorescent labeled liposomes containing both LPS and poly (I:C), it was demonstrated that such liposomal LPS-poly(I:C) cocktail is able to enter into contact with zebrafish hepatocytes (see Figure 1b) and trout macrophage plasma membranes at short incubation times, being preferentially internalized through caveolaedependent endocytosis, although clathrin-mediated endocytosis in ZFL cells and macropinocytocis in macrophages. Importantly, we anticipate that this liposomal LPS-poly(I:C) cocktail elicits a specific proinflammatory and anti-viral response in both zebrafish hepatocyte cells and trout macrophages, after studying the changes in the expression of different immune related genes. The design of a unique delivery system with the ability to stimulate two potent innate immunity pathways virtually present in all fish species represents a completely new approach in fish health [4]. Further work is ongoing to evaluate the in vivo biodistribution and portals of entry of the liposomal LPSpoly(I:C) cocktail in three aquacultured fishes (trout, seabream and seabass), which will allow us to compare different ways of administration (injection, oral and immersion) and to design rational immunisation protocols.

REFERENCES [1] O. Evensen, Development in fish vaccinology with focus on delivery methodologies, adjuvants and formulations, Options Mediterraneennes. (2009) 1–10. [2] R.L. Coffman, A. Sher, R.A. Seder, Vaccine Adjuvants: Putting Innate Immunity to Work, Immunity. 33 (2010) 492–503. [3] O. Takeuchi, S. Akira, Pattern Recognition Receptors and Inflammation, Cell. 140 (2010) 805–820. [4] L.-Y. Zhu, L. Nie, G. Zhu, L.-X. Xiang, J.-Z. Shao, Advances in research of fish immune-relevant genes: A comparative overview of innate and adaptive immunity in teleosts, Dev Comp Immunol. (2012) 1–24.


Enzymatic Growth of Quantum Dots: Applications to Probe Glucose Oxidase and Horseradish Peroxidase and Sense Glucose Laura Saa, Valeri Pavlov CIC biomaGUNE, Paseo Miramon 182, 20009, San Sebastian, Spain lsaa@cicbiomagune.es

Abstract Quantum Dots (QDs) have been generally used as fluorescent labels in biosensing, especially in assays based on detection of analytes by affinity binding.

The background signal of these bioanalytical

systems is quite high due to nonspecific adsorption of decorated QDs on surfaces or poor quenching of a donor couple. Enzymatic growth of QDs in situ triggered by a biorecognition event potentially can solve the problem of the high background signal, improve sensitivity and diminish costs of analytical assays and could use a much more sensitive fluorescence spectroscopy. We developed three innovative assays to detect enzymatic activities of glucose oxidase (GOx) and horseradish peroxidase (HRP) by generation of CdS QDs in situ using non-conventional enzymatic reactions. In the first assay GOx catalyzes the oxidation of 1-thio-β-D-glucose to give 1-thio-β-Dgluconic acid. The latter is spontaneously hydrolyzed to β-D-gluconic acid and H2S, which in the presence of cadmium nitrate yields fluorescent CdS nanoparticles. In the second assay HRP catalyzes the oxidation of sodium thiosulfate with hydrogen peroxide generating H2S and consequently CdS QDs. The combination of GOx with HRP, allowed quantification of glucose in plasma by following growth of fluorescent QDs. These systems can provide models for numerous peroxidase and oxidase-based biosensor assemblies.

Scheme 1. Enzymatic generation of CdS QDs for the detection of redox enzymes.


Design and synthesis of carbon encapsulated iron nanoparticle for drug delivery M. Reza Sanaee, S. Chaitoglou, V.-M. Freire, N. Aguiló-Aguayo, E. Bertran FEMAN Group, Institute of Nanoscience and Nanotechnology (IN2UB), Dep. Applied Physics and Optics, Universitat de Barcelona, Martí Franquès, 1, E08028 Barcelona, Spain sanaee@ub.edu Magnetic nanoparticles are being of great interest because of their unique properties especially in drug delivery, magnetic resonance imaging and cell separation. In many clinical situations, medication doses are oversized as a result of impaired drug absorption or tissue unspecific delivery [1]. The ultimate goal of magnetically controlled drug delivery and drug therapy is to selectively delivering drug molecules to the diseased site without a concurrent increase in its level in healthy tissues. In this research study, carbon encapsulated iron nanoparticles (CEINPs) were designed and produced by arc discharge method in a way to make them as suitable nanocarriers. It has been reported that a particle size range of 50–300 nm is strictly demanded [2]. Barbe et al [3], proposed a novel drug delivery system. They studied drug release of silica nanoparticles with both sizes of 50 nm and 250 nm in different organs, and their 250 nm particles did not trapped by lung capillaries. Moreover, an optimum geometry for endocytotic uptake is 50 nm and spherical particles are more easily internalized compared to elongated particles [4 & 5]. One of the disadvantages of using magnetic nanoparticles is the risk of their magnetic interaction and hence their agglomeration and blockage of vein. To overcome this difficulty, the magnetic particles are covered by carbon shell. According to the TEM and SEM observations the carbon shell is spherical and their median size is 220 nm and the iron core is 3 nm, (Figure 1). Generally, due to the size distribution of iron nanoparticles there are some iron particles which are not superparamagnetic and therefore a large carbon shell is necessary to open enough space between iron particles. The magnetic properties are characterized by SQUID. Accordingly, their superparamagnetic behavior is investigated at body temperature (Figure 2). Moreover, the blocking temperature is very low (Figure 3). The crystallinity of carbon shell and surface properties are characterized by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR), respectively. Consequently, carbon shell shows less defect and high crystallinity and FTIR spectrum illustrates the suitability of surface for further functionalization and modification (Figure 4). Nanoparticles can control the basic functions of cells, and potentially kill cancer cells, by virtue of their size alone without the need for drugs [6]. As the conclusion, produced particles fulfill the requirements of drug delivery and therapeutic applications in terms of size, shape, magnetic and surface properties. In addition, carbon shells are biocompatible and thermally stable. References 1- E. Ruiz-Hernández , A. Baeza , and M. Vallet-Regí, ACS Nano, 5 (2011) 1259–1266. 2- W. Zhao, J. Gu, L. Zhang, H. Chen, and J. Shi, Journal of American Chemical Society, 127 (2005) 8916-8917. 3- C. Barbe, J. Bartlett, L. Kong, K. Finnie, H. Q. Lin, M. Larkin, S. Calleja, A. Bush, and G. Calleja, Advanced Materials, 21 (2004) 1959-1966. 4- P. Decuzzi, R. Pasqualini, W. Arap and F. Mauro, Pharmaceutical Research, 26 (2009) 235-243. 5- W. Jiang, B. Y. Kim, J. T. Rutka and W. C. W. Chan, Nature, 3 (2008) 145-150. 6- M. Ferrari, Nature, 3 (2008) 131-132.


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Figure 1. A) TEM image of small iron particle, B) SEM image of spherical CEINPs

Figure 2. Hysteresis loop of CEINPs at body temperature

Figure 4. FTIR spectra of CEINPs

Figure 3. Zero-field-cooled and field-cooled magnetization curves


DEVELOPMENT OF FLUORESCENCE TECHNIQUES FOR THE EVALUATION OF ANTIBODY CONJUGATION TO MICROSPHERES Suárez B., Berganza J., Garay I., Goñi F., Rosé Z. & Barrenetxea Z. Gaiker Technology Centre, Parque Tecnológico Edif. 202, 48170, Zamudio, Spain suarezb@gaiker.es In the last years, the development of new strategies for a more sensitive and accurate analysis of biomarker molecules in health, food and environmental samples has been very promoted. In a biosensor, a biological target and a ligand bind in a reaction that is collected as signal to a transducer using different technologies (optics, electrochemistry, magnetism, etc...). The use of the physical properties of micro and nanoparticles in the development of biosensors has represented a great advantage. In some cases, magnetic particles are used as carriers of antibodies to immunomagnetic separation in complex samples. In other cases, particles labelled with fluorochromes could be detected in a detection system by their fluorescent signal. Antibody conjugation to particles can be obtain by adsorption (at the isoelectric point of the antibody via electrostatic interaction), by direct covalent linkage between the surface of particle and the antibody, or by using bridge molecules (like streptavidin-avidin complex). In covalent linkage, optimal bioconjugation would involve the stable attachment of the antibody through his Fc region to surface particle leaving the antigen-binding site Fab region full functional. This work evaluate different methods for determinate the antibody conjugation efficiency on particle surface. Materials and methods: In this study we have worked with Dynabeads® M-270 of Invitrogen, 2,80 m size, mainly for two reasons: -

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We were looking for surface-modified microspheres and for a strong attachment of antibodys to them, and carboxyl-modified microspheres meet these requirements. As it is extensively defended in literature, activation of carboxyl-modified microspheres can be performed with a carbodiimide followed by coupling of an amine containing ligand, resulting in a stable amide bond between the bead and the ligand, We were interested to work with magnetic microspheres, knowing that magnetic particles have been utilized extensively in diagnostics and other research applications for the capture of biomolecules because they confer a number of benefits, including ease of separation.

Selected antibody to be linked to the beads was a mouse monoclonal. For the visualization of conjugation yields of a mouse antibody to these microspheres, we have used different techniques based on fluorescence phenomenon: -

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Fluorescence microscopy (confocal microscopy): a non-quantitative technique that allows visualization of the distribution of the antibody through the microsphere. Flow cytometry: a quantitative technique that lets users to know information about the physical and chemical structure of each individual particle present in the sample, and extrapolate it to the entire sample as a mean value of fluorescence emitted for it. At least, 20.000 beads per single determination were measured. Immunofluorescence techniques: two quantitative techniques have been evaluated. The first one allows us to quantify the antibody that is chemically linked to a fluorophore and that has not been linked to the microsphere, and the second one measures the fluorescent antibody that has been linked to the beads.

To evaluate the mouse antibody conjugation efficiency on 2,8 m particle surface an anti-mouse Alexa Fluor 488 antibody has been used.


Results and discussion: Confocal microscopy: Fluorescent

2,8 µm magnetic

Visually it was confirmed the linkage of mouse antibody to the beads through the union of this antibody to an antimouse Alexa Fluor 488 antibody. Flow cytometry: As it was expected, as much as antimouse Alexa Fluor 488 was added to conjugated beads, higher was the fluoresecence found in the sample, until achieved a maximum in which there are no free mouse antibody on the bead to be linked with. Nevertheless, since we didn’t have standards of these beads conjugated with the same antibody in different concentrations, using this result, we couldn´t determine the number of molecules of mouse antibody linked to each bead. Immunofluorescence techniques: Taking into account the number of beads in the sample and maximum of antimouse Alexa Fluor 488 linked to them, we concluded that the number of molecules of mouse antibody that were linked to each 5 2,8 m microsphere was 3*10 . This result was achieved analyzing both, the antimouse Alexa Fluor 488 that has not been linked to the microsphere, and the antimouse Alexa Fluor 488 that has been linked to the beads.

Although the number of molecules of mouse antibody that can be bound to the beads was quantified, the main objective of this research was to determine the number of them that maintained their functionality after being linked to the microspheres. Further assays are under development in order to achieve this goal using an indirect method: an antibody that is chemically linked to a fluorophore is linked to a target molecule that previously was bound to the mouse antibody present in the beads.

Target molecule Fluorescent

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Synthesis of graphene oxide – Fe3O4 nanoparticles hybrid K. Urbas, M. Wojtoniszak, R. Rakoczy, E. Mijowska, R.J. Kalenczuk

West Pomeranian University of Technology, Institute of Chemical and Environment Engineering, Pulaskiego 10, 70-322 Szczecin, Poland kurbas@zut.edu.pl

Abstract Graphene is a one – atom – thick planar sheet of carbon atoms densely packed in a honeycomb cristal lattice. Due to its exceptional electronical, physical, chemical and mechanical properties, graphene, graphene oxide and reduced graphene oxide have been extensively studied for a variety of applications in biomedicine[1-3]. Monolayer of carbon atoms, two dimensional structure and high specific surface area make it a perfect potential carrier for a large number of substances, e. g. biomolecules, drugs, ferromagnetic nanoparticles. Magnetite (Fe3O4) has been widely used in various fields such as targeted drug delivery, hyperthermia, magnetic resonance imaging because of its magnetic and electrochemical properties [4-5]. We report a facile method for the preparation of graphene – oxide – Fe3O4 nanoparticles hybrid. The surface of iron oxide was modified with oleic acid. The carboxylic groups on the graphene oxide surface were activated with N-Hydroxysuccinimide (NHS) and 1-(3-dimethylaminopropyl)-3ethylcarbodiimide (EDC). The mixture of modified iron oxide and graphene oxide was stirred for 48 h. Transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT – IR), thermal gravimetric analysis (TGA) and X – ray diffraction technique (XRD) were used to characterize the obtained product. The XRD pattern of graphene oxide – Fe3O4 hybrid is presented in Fig. 1. It shows reflections consistent with the magnetite which is known for its magnetic properties. Fig. 2 presents the TEM image of graphene – oxide – Fe3O4 nanoparticles hybrid.

References [1] Liu, Z., Robinson, J. T., Sun, X., and Dai, H., J. Am. Chem. Soc., 130 (2008) 0876 – 10887. [2] Zhang, Y., Nayak, T. R., Hong, H., and Cai, W., Nanoscale, 4 (2012) 3833 – 3842. [3] Wang, Y., Li, Z., Wang, J., Li, J., and Lin, Y., Trends in Biotechnology, 29 (2011) 205 – 212. [4] Yang, X., Zhang, X., Liu, Z., Ma, Y., Huang, Y., and Chen, Y., J. Phys. Chem. C, 112 (2008) 17554 – 1 7558. [5] Yu, M. K.; Jeong, Y. Y.; Park, J.; Park, S.; Kim, J. W.; Min, J. J.; Kim, K.; Jon, S. Angew. Chem., Int. Ed., 47 (2008) 5362. [6] Larsen, E. K. U.; Nielsen, T.; Wittenborn, T.; Birkedal, H.; Vorup – Jensen, T.; Jakobsen, M. H.; Ostergaard, L.; Horsman, M. R.; Besenbacher, F.; Howard, K. A.; Kjems, J., ACS Nano, 3 (2009) 1947. [7] Geim, A. K.; Novoselov, Nat. Mater., 6 (2007), 183 – 191. [8] Park, S.; Ruoff R.S., Nat. Nanotechnol., 4(4) (2009) 217 – 24. [9] Rao, C. N. R.; Sood, A. K.; Subrahmanyam, K. S.; Govindaraj, Chem., Int. Ed., 48 (2009) 7752 – 7777.


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Fig.1. XRD pattern of graphene – oxide – Fe3O4 nanoparticles hybrid.

Fig. 2. TEM image of graphene – oxide – Fe3O4 nanoparticles hybrid.


Adsorption of proteins on nanoparticles: the effect of curvature and size Oriol Vilanova1, Pol Vilaseca1, Kenneth A. Dawson2, Giancarlo Franzese1 1

Departament de Física Fonamental, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain 2 Center for BioNano Interactions (CBNI), University College of Dublin, Ireland ovilanova@ffn.ub.es

Abstract Cellular responses to materials in a biological medium reflect greatly the adsorbed biomolecular layer, rather than the material itself. Here, we study by molecular dynamic simulations the competitive protein adsorption on surfaces, i.e. the non-monotonic behavior of the amount of protein adsorbed on a surface in contact with plasma as a function of contact time and plasma concentration. We study the effects of different curvatures and nanoparticles size when the surface chemistry is the same. [1] References [1] P. Vilaseca, K. A. Dawson, and G. Franzese, “Understanding surface-adsorption of proteins: the Vroman effect”, arXiv:1202.3796v2 (2012).


A CMOS-Compatible, low-energy consumption Franz-Keldysh effect Plasmonic Modulator Active Region Nicolas Abadia, Papichaya Chaisakul, Delphine Marris-Morini and Laurent Vivien Institut d'Electronique Fondamentale Bât. 220 Université de Paris-Sud XI 91405 Orsay - France nicolas.abadia@u-psud.fr Ségolène Olivier and Roch Espiau de Lamaestre CEA-LETI, MINATEC Campus 17 Rue des Martyrs 38054 Grenoble - France Thomas Bernardin and Jean-Claude Weeber Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne, 9 Avenue A. Savary 21078 Dijon - France Abstract In this abstract we report on the design of a low energy consumption CMOS-compatible FranzKeldysh effect plasmonic modulator. The main characteristics of the modulator were determined using integrated electro-optical simulations. A 3.3 dB extinction ratio for a 30 µm long modulator was demonstrated under 3 V bias voltage at an operation wavelength of 1647 nm. The estimated energy consumption was as low as 20 fJ/bit. This is the lowest energy consumption reported with photonic Franz-Keldysh effect modulators. The structure of the modulator proposed is presented in Fig. 1. It consists in a classical vertical MIS plasmonic slot waveguide formed by Copper (Cu), Silicon Nitride (Si 3N4) and Germanium (Ge). The Si3N4 diffusion barrier has a thickness h Slot and the Ge core has a width w and a height h. Such a structure stands on a p-doped Ge (p-Ge) layer of height h Bot which is over a p-doped Si layer (p-Si) of height hBuf. Everything is encapsulated by SiO 2. The structure has two electrical contacts: one in the top Cu material and the other in the p-Ge and p-Si. Such a structure is CMOS-compatible, as it can be fabricated on a SOI substrate using microelectronics tools.

 Cu  Si3N4 SiO2

    p-Ge   p-Si

hSlot Ge (nid)  

 

h hBot hBuf

  w Fig. 1: Cross section of the Franz-Keldysh effect plasmonic modulator The active principle of the modulator is to use the Franz-Keldysh (FK) effect [1,2] in order to modulate the plasmonic mode supported by the slot waveguide. The FK effect is the change in absorption that a material experiences under the influence of a static electric field. The change in the absorption occurs close to the band-edge energy of the material, i.e. at the wavelength of 1647 nm in strained Ge grown on silicon. This slot waveguide supports a plasmonic mode whose electric field is concentrated mainly in the Si3N4 slot and in the Ge core. When a voltage V is applied between the contacts, a static electric


field appears in the Ge core. This static electric field changes the absorption of the material Ge present in the core, due to the FK effect. As a consequence, the effective loss of the plasmonic mode is also changed, thus producing the intensity modulation at the output of the waveguide. In this work, we performed an integrated electro-optical simulation in order to deduce the characteristics (modulation depth, insertion losses, etc.) of the plasmonic modulator of Fig. 1. For this purpose, we used a commercial electrical simulator ISE-DESSIS in order to calculate the static electric field distribution when a voltage V is applied between the two contacts. Knowing the static electric field in the Ge core, the change in the absorption of the material due to the FK effect can be calculated using a known theoretical model [3]. Finally, using a Finite Difference Method (FDM) optical mode solver with the absorption distribution, we are able to calculate the effective propagation losses of the plasmonic mode. From this value we can calculate the modulation depth of the device for a given length. Using this method we optimized the device in order to increase the modulation depth, reduce the insertion losses and the energy consumption. Regarding the energy consumption, we used the model described in [4]. In this model the energy consumption of the dynamic modulation is given by the formula E bit=1/4CVDD2 where C is the capacitance of the device and VDD is the driving voltage. Using the electrical simulator ISE-DESSIS we found a capacitance of around C=9 fF for a device length of 30 μm. Using this value, the energy per bit is found around 20 fJ/bit, which is lower than for state-of-the-art photonic FK effect modulators [5-10]. This makes plasmon-assisted Franz-Keldysh modulators promising candidates for future optical links. References [1] W. Franz, “Einfluß eines elektrischen Feldes auf eine optische Absorptionskante”, Z. Naturforschung 13, 484–489 (1958) [2] L. V. Keldysh, “Behaviour of non-metallic crystals in strong electric fields”, J. Exptl. Theoret. Phys. (USSR) 33, 994–1003 (1957) [3] H. Shen and F. H. Pollak, “Generalized Franz-Keldysh theory of electromodulation”, Physics Review B 42, 7097–7102 (1990) [4] David A. B. Miller, “Energy consumption in optical modulators for interconnects”, Optics Express 20, A293-A308 (2012) [5] S. Jongthammanurak, J. Liu, K. Wada, D. D. Cannon, D. T. Danielson, D. Pan, L. C. Kimerling and J. Michel, “Large electro optic effect in tensile strained Ge on Si films”, Applied Physics Letters 89, (2006) [6] J. Liu, D. Pan, S. Jongthammanurak, K. Wada, L. C. Ki-merling and J. Michel, “Design of monolithically integrated GeSi electroabsorption modulators and photodetectors on an SOI platform”, Optics Express 15, 623-628 (2007) [7] J. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling and J. Michel, “Waveguide integrated ultralow energy GeSi electro-absorption modulators”, Nature Photonics 2, 433437 (2008) [8] A. Eu-Jin Lim, T. Liow, F. Qing, N. Duan, L. Ding, M. Yu, G. Lo and Dim-Lee Kwong, “Novel evanescent coupled germanium electro absorption modulator featuring monolithic integration with germanium PIN photodetector”, Optics Express 19, 5040-5046 (2010) [9] N. Feng, D. Feng, S. Liao, X. Wang, P. Dong, H. Liang, C. Kung, W. Qian, J. Fong, R. Shafiiha, Y. Luo, J. Cunning-ham, A. V. Krishnamoorthy and M. Asghari, “30 GHz Ge Electro Absorption Modulator Integrated with 3 μm Silicon on Insulator Waveguide”, Optics Express 19, 7062-7067 (2011) [10] D. Feng, S. Liao, H. Liang, J. Fong, B. Bijlani, R. Shafiiha, B. J. Luff, Y. Luo, J. Cunningham, A. V. Krishnamoorthy and M. Asghari, “High Speed GeSi EA Modulator at 1550 nm”, IEEE, 355-357 (2012)


Partially Coherent Forces on Submicrometer Magnetodielectric Particles Juan Miguel Auùón and Manuel Nieto Vesperinas Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas. Campus de Cantoblanco, Madrid, 28049, Spain jmaunon@icmm.csic.es In this work we investigate the photonic forces from three-dimensional electromagnetic field emitted by a three-dimensional fluctuating homogeneous and isotropic source. This primary source will induce electric, and in this case also magnetic, dipoles in the particle. These induced dipoles will also be considered as a secondary source which will interact with the primary source, originating a new force on themselves [1]. In order to see the effects on a magnetodielectric particle we consider a semiconductor particle, with a real refraction index such as Silicon. In this type of particles, in the range of the near infrared, the total cross section can be determined uniquely by the two first electric, and magnetic, Mie coefficients, thus, the total force can be calculated using the dipolar approximation instead of the Maxwell's stress tensor . In the attached figure we show the force from the primary (first row) and the secondary (second row) sources. The electric, magnetic and electric-magnetic interference forces are shown for a zero coherence length of the source. In near-field, the behavior and the change of the sign in this force is due to that of the polarizability of the particle considered (see the plots inset). We can easily see that, whereas the force from the primary source is constant for any distance from the source larger than 2.5 times the wavelength, the force from the above mentioned induced secondary source oscillates and tends to zero with increasing distance due to the homogeneous waves. In the near-field, the total force (the sum of all the components) will be governed by the secondary source, nevertheless, as we go away from the plane of the source, the homogeneous waves of the field emitted by the primary source will predominate. In this regard, it is worth remarking that in Fig. 1(c) we see a zone where the force will be negative and constant for any distance. The magnitude of this last force is one order lower than that from the primary source; thus it does not dominate; however, manipulating the properties of the electromagnetic field we could have a tractor force [4] In summary, we have shown, that the mechanical action on a magnetodielectric particle from the electromagnetic field emitted by a primary source cannot be totally determined unless one takes into account the induced dipole as a new source. This effect is extremely important at distances shorter than the wavelength.


References [1] J.M. Auñón and M. Nieto-Vesperinas (to be published). [2] A. García-Etxarri et al. “Strong magnetic response of submicron Silicon particles in the infrared”. Optics Express, 19, 4815 (2011) [3] M. Nieto-Vesperinas et al. “Angle-suppressed scattering and optical forces on submicrometer dielectric particles”. Journal of the Optical Society of America A, 28, 54 (2011) [4] A. Novitsky et al. “Single Gradientless Light Beam Drags Particles as Tractor Beams”. Physical Review Letters, 107, 203601 (2011)

Figures

First row: Electric, magnetic and interaction forces from the primary source normalized to the spectrum of the force. The insets show the behavior of the polarizability (normalized to the radius³) in the range of wavelengths considered (adapted from [3]) Second row: The same as the first one for the secondary source (the induced dipoles)


Embedding grating mirror in resonant cavity-enhanced absorber structures for mid-infrared detectors applications 1

1

1

Mark Auslender, Moshe Zohar, Shlomo Hava, L. Faraone

2

1

Ben-Gurion University of the Negev, Department of Electrical and Computer Engineering, POB 653, Beer-Sheva 84105, Israel 2 The University of Western Australia, School of Electrical, Electronic and Computer Engineering, Crawley 6009, Australia marka@ee.bgu.ac.il Abstract Incorporating a photosensitive (optically active) layer into Fabry-Perot (FP) cavity enhances the layer's sensitivity (emissivity) due to reflections of light between the cavity mirrors. Strongest enhancement occurs when the phase difference between each succeeding reflection (round-trip phase), satisfies the resonance condition (which is in fact that of highest resonant transmission through empty FP cavity) 0

where

0

4 nc

0

is a resonance wavelength,

the cavity;

f

and

b

tc

0

f

0

b

0

2 m,

(1)

m is an integer; nc and tc is refractive index (RI) and length of

is the reflection phase of front and back FP cavity mirror, respectively.

High performance photo-detectors (PDs) and imagers in MWIR range (3-10 m) are attracting increasing interest due to the wide applications in security surveillance, chemical sensing, and industrial processes monitoring [1, 2]. Promising technology is using the resonant cavity enhanced (RCE) absorption [3]. So far, the RCE PDs designs commonly employed [3] distributed Bragg reflectors (DBRs), i.e. stacks of quarter-wave pairs of high/low (H/L) RI layers, both for the front mirror (one that is further away from the illuminated side) and back mirror, as shown in e.g. Fig.1(a). In this presentation, we propose RCE PDs in which the front mirror is a grating structure, designed to act as perfect retro-reflector, and the back mirror is a DBR. Optical absorbance of a thin semiconductor embedded in the resonant cavity of this novel type (assuming that the absorption is efficiently converted into photoconductive or photovoltaic response) is further maximized. We apply this idea to Hg0.7Cd0.3Te in a CdTe cavity [4]. In our design shown in Fig. 1(b) the irradiation and back mirror (Hg0.6Cd0.4Te/CdTe DBR grown on a CdZnTe substrate) scheme is the same as in the conventional design [4], shown in Fig.1(a), while the front mirror is the Ge-grating/layer structure, instead of Ge/SiO DBR. For a fair comparison, we optimized both conventional and grating-based RCE HgCdTe(MCT)-absorber structure using smart round-trip and mirrors' phases engineering. The optimization results are presented in Table 1 and the simulated absorption (A) spectra of the structures are shown in Fig.2. Some of the structural parameters in Table 1 are depicted in Fig.1 and some defined in its caption. The optimized grating-mirror based RCE MCT-absorber attains efficiency ~100% with the mirrors twice thinner than in the conventional one that cannot be optimized furthermore. The obtained results indicate that the novel grating-mirror based type of RCE PDs meets the combined challenges of significantly increasing the efficiency and reducing the overall complexity and size of the entire device, in comparison with the conventional RCE PDs. Table 1 The parameters of designed conventional and grating-based RCE MCT-absorber structures, RCE-C and RCE-G, respectively; tFM and tBM is the front and back mirror total thickness, respectively Structure RCE-C RCE-G

db, m 0.272 0.05

ta, m 0.075 0.075

df, m 0.433 0.429

tFM, m 2.082 0.880

tBM, m 12.15 5.867

tg, m – 0.255

Λ, m – 1.383

W/Λ – 0.36

Peak A 83 % 97 %

References [1] J. Wang, J. Hu, P. Becla, A.M. Agarwal, L.C. Kimerling, Opt. Express., vol. 18 (2010) 12890. [2] A. Rogalski, J. Antoszewski, L. Faraone, J. Appl. Phys., vol. 105 (2009) 091101. [3] M. S. Unlu, S. Strite, J. Appl. Phys., vol. 78 (1995) 607. [4] J.G.A. Wehner, R.H. Sewell, J. Antoszewski, C.A. Musca, J M. Dell, L. Faraone, J. Electron. Mater., vol. 34 (2005) 710.


Figures

DBR 2

(HL) H

tc

df

CdTe HgCdTe

db

CdTe

Front Grating Mirror

tGe

df ta db

ta

CdTe HgCdTe CdTe

0.9

tGe

Ge

DBR

(HL)15H

(HL)7H

tHgCdTe

tc

W

CdTe

HgCdTe

CdTe

CdTe

HgCdTe

HgCdTe

RCE-O RCE-TM

0.8

HgCdTe

tCdTe

DBR

HgCdTe

tg

Ge Air

tSiO

HgCdTe CdTe

1

W

Absorbance, A [abs. u.]

Ge SiO Ge SiO Ge

0.7 0.6 0.5 0.4 0.3 0.2 0.1

CdZnTe Substrate/Input medium (a)

0

CdZnTe Substrate/Input medium

4.25

4.3

4.35

4.4

4.45

4.5

4.55

4.6

Wavelength [ m]

(b)

m

Fig.1. RCE MCT-absorber structures with (HL) H k back mirror and the DBR (HL) H front mirror (a) or the grating-based front mirror (b).

Fig.2. Absorbance spectra of the conventional and grating-mirror based optimized RCE MCTabsorber structures, displayed in Table 1


Experimental studies of narrow plasmon resonances in asymmetric environment in diffractive arrays of gold nanoparticles

Andrey G. Nikitin, and Tuyen Nguyen and Hervé Dallaporta Aix-Marseille University, CINaM-CNRS, Campus de Luminy, Case 913, 13288 Marseille, France dallaporta@cinam.univ-mrs.fr Abstract The plasmon resonances in asymmetric refractive index environment in two-dimensional diffractive arrays of gold nanoparticles can be a good candidate for biosensing purposes. We will present the experimental transmission spectra obtained for different sizes, shapes and periodicities and demonstrated the ability to tune the wavelength of these resonances in the near infrared range. Diffraction of metallic gratings is well-known since many years to provide a way to excite of 1-4 surface plasmon polaritons. In a same spirit, the properties of the localized plasmons can be manipulated using the diffraction that take place in regular arrays of metal nanoparticles. The narrowing of the plasmon resonance lineshape induced by the diffractive coupling has been widely demonstrated 5-9 10-17 by theoretical modeling and optical experiments . This collective excitation of localized plasmons 10 of particules is now referred as collective resonances (CRs) . Since for biosensing, the nanostructures must be immersed in medium (superstrate medium) with refractive index very different compare to the one of the substrate, we have studied the transmission spectra of ordered Au nanoparticle arrays in asymmetric environment. In this contribution, we will presented the transmission spectra of periodic arrays of gold nanoparticles fabricated on a glass substrate (refractive index =1.5) coated with a 20 nm thick indium tin oxide (ITO). The 100 µm×100 µm gold patterns were transferred from a PMA e-beam lithography resist adding a 3nm thick Cr layer to increase the gold adhesion on ITO. The nanoparticles are arrange in a square lattice array with two different shapes: 50nm height cylinders with 120 nm, 150 nm and 170 nm diameter and 50nm thick nanorod with in-plane dimensions of 120 nm × 200 nm. . The transmission spectra were measured at quasi normal incidence on a collimated spot (30µm) using Woollam M2000 spectroscopic ellipsometer. Figure 1 (a and b) gives examples of transmission spectra for asymmetric configuration for different values of the top medium refractive index (glycerol =1.47, water =1.33 and air =1) and for different values of the array period. The spectra exhibit localized dip adsorption features that correspond to the excitation of CRs. Due to the modification of the coupling between of the single particule localized plasmons by changing the distance between nanoparticles, the resonance of the array experience anomalous spectral shifts. Furthermore, the spectral lineshape is considerably modified as compare to single nanoparticle case. As it has been obtained for symmetric cases, the 6,7,10 resonant dip redshifts and its spectral lineshape gets narrower as the lattice period increases . Since for biosensing, the interest is in the change of resonance shape and shift induced by the change of the refractive index, we give on fig 1 (d) the resonance shifts and the factor of merit (FOM) versus the lattice period. From our results, we will discuss the possibilities that diffractive coupling offer to adjust the width and the wavelength of plasmon resonance by changing the size and geometry of constituent nanoparticles. From the optical transmission spectra of ordered arrays of gold nanoparticles in asymmetric configuration, we can study the influence of collective effect on plasmon resonances and evaluate the performances that can be obtained on diffractive gold nanoparticle arrays as a sensor.


References 1 R. W. Wood, Philos. Mag. 4(21), 396–402 (1902). 2 U. Fano, J. Opt. Soc. Am. 31(3), 213 (1941). 3 A. Hessel and A. A. Oliner, Appl. Opt. 4(10), 1275 (1965). 4 D. Maystre, M. Nevière J. Opt. 8, 165 (1977). 5 V. A. Markel, J. Phys. B.: Mol. Opt., 38, L115-L121 (2005). 6 S. Zou, N. Janel, and G. C. Schatz, J. Chem. Phys. 120, 10871-10875 (2004). 7 S. Zou and G. C. Schatz,. J Chem. Phys. 121, 12606–12612 (2004). 8 F. J. G. de Abajo, Rev. Mod. Phys. 79(4), 1267-1290 (2007). 9 W. Hu and Sh. Zou, J. Phys. Chem. C15(35), 17328-17333 (2011) 10 B. Auguié and W. L. Barnes, " Phys. Rev. Lett. 101, 143902-143906 (2008). 11 V. G. Kravets, F. Schedin, and A. N. Grigorenko, Phys. Rev. Lett. 101, 087403 (2008). 12 Y. Z. Chu, E. Schonbrun, T. Yang, and K. B. Crozier, Appl. Phys. Lett. 93(18), 181108 (2008). 13 G. Vecchi, V. Giannini, and J. Gomez Rivas, Phys. Rev. B 80, 201401 (R)(2009). 14 G. Vecehi, V. Giannini, and J. Gomez Rivas, Phys. Rev. Lett. 102(14), 146807 (2009). 15 V. Giannini, G. Vecchi, J. Gomez Rivas,. Phys. Rev. Lett. 105, 266801 (2010). 16 P. Offermans, M. C. Schaafsma, S. R. K. Rodriguez, Y. Zhang, M. Crego-Calama, S. H. Brongersma, J.Gomez Rivas, ACS NANO 5, 5151-51 57 (2011). 17 W. Zhou and T. W. Odom, Nat. Nanotechnol. 6(7), 423427 (2011).

Figure

Fig. 1: Transmission spectra of periodic 170nm gold cylinder arrays for different superstrate media: (a) water (thick line), glycerol (thin line) and (b) air. Spectra are shifted by 0.2 units along y axis. (c) Resonance dip wavelength as a function of the lattice period. (d) Shift of the resonance dip in nm per RIU obtained from the spectra in panel (a) and FOM for the arrays with different lattice periods. Inset: scanning electron microscope image of 450 and 700 nm arrays.


Looking inside photonic nanowires with coherent X-ray imaging M. Elzo Aizarna(1,2,3), F.Mastropieto(4) V. Favre-Nicolin(1,2), Joel Eymery(1), D. Carbone(3), Joel Bleuse(1), J.Claudon (1), J.M Gerard(1) CEA-UJF, INAC, SP2M, 17, rue des Martyrs 38054 Grenoble, France (2) Univ. Grenoble Alpes, F38041 Grenoble, France (3) ESRF, 6 rue Jules Horowitz 38043 Grenoble, France, (4) IM2NP, Univ. AixMarseille, France (1)

marta.elzoaizarna@cea.fr Abstract The development of efficient single-photon sources is a key step required for the progress of efficient quantum communications. Such a device would allow to emit on-demand light pulses containing exactly one photon. Such a source was recently developed at INAC/CEA Grenoble (France), using InAs quantum dots (QDs) embedded in a GaAs nanowire. The InAs QDs act as single photon sources, for which the exact wavelength varies with the shape and size of the QDs. The GaAs nanowire (diameter ~600 nm) acts as an optical wave-guide [1] (figure 1). The photo-emission properties are studied by micro-photoluminescence (ÂľPL) measurements as shown in (figure 2). The spectral lines come from individual dots and it is possible to separate them as long as there are few dots (<10) in the wire. Each dot has a unique spectral line because they are all different in size, shape and position within the same nanowire. Therefore in order to improve these photonic devices, it is necessary to understand the relationship between the ÂľPL measurements and the size, position and location of the QDs. The structural properties are studied via the deformation field created by the QDs inside the nanowire. Coherent X-ray Diffraction Imaging (CDI) provides a 3D image of the density distribution and also the projection of the strain along the Bragg reflection. The scattering intensity around a Bragg reflection is sensitive to the deformation of the crystal, at a resolution smaller than the d-spacing of the considered reflection. Moreover with X-rays, it is possible to study buried objects without sample preparation that might change their strain state.[3] The final image of the studied sample is obtained by reconstructing the experimental results using interative algorithms based on Fourier Transformation. Here we present CDI measurements on GaAs nanowires with embedded InAs QDs measured in two different ways: with Coherent 3D Bragg diffraction (figure 3) and with Ptychograpy (figure 4). For the first case the 3D images are obtained by scanning the reciprocal space with a 2D detector. With Ptychography the sample is scanned along the wire with overlapping illuminating areas. For the latter we also show reconstructed nanowire with the embedded QD (figure 5)[4]. References [1] J. Claudon et al. Nature Photon, 4, (2010) 174. [2] Favre-Nicolin V. et al. New Journal of Physics 12 (2010), 35013. [3] Robinson, Ian, & Ross Harder. Nature Materials 8 (2009),291-298. [4] Mastropietro F., PhD Thesis, Univ. Grenoble (2011) Figures


Figure 1: Scanning electron microscopy images of the investigated nanowire with InAs QDs.

200 nm

Figure 2: ÂľPL measurements of 200 nm diameter nanowire. The multiple ÂľPL lines come from single QDs inside the nanowire.

Figure 3: 3-dimensional diffraction pattern collected at the QDs position for the (115)GaAs Bragg reflection.

Figure 4: 2D scatterings from a vertical scan along the GaAs wire with for two values of the scan.

Figure 5: Reconstructed shape of the nanowire. The color difference at z=0 corresponds to the insertion of the QD.


Generation of picosecond acoustic pulses in cobalt by ultrashort electron pulses in gold 1

1

1

1

2

Oleksandr Kovalenko , Viktor Shalagatskyi , Thomas Pezeril , Vitalyi Gusev , Denys Makarov , 2 2 1 Luyang Han , Oliver G. Schmidt and Vasily V. Temnov 1

Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Université du Maine, 72085 Le Mans cedex, France. 2 Institute for Integrative Nanosciences, IFW Dresden, 01069 Dresden, Germany oleksandr.kovalenko.etu@univ-lemans.fr

Abstract Generation of ultrashort hot electron pulses in metals by femtosecond laser pulses [1] as well as the ultrafast electronic heat transport and energy transfer to the lattice, resulting into the emission of coherent acoustic pulses [2-4] were discovered two decades ago. However, mainly due to the technological limitations in sample fabrication, many fundamental questions such as the efficiency of heat transport by ballistic electrons as compared to diffusive transport remained unclear. Nowadays, the electronic properties of different metallic compounds based on hybrid metal-ferromagnet multilayer structures attract particular interest because of their applications in ultrafast spintronics [5] and magneto-plasmonics [6]. Very recently, ultrafast plasmonic studies allowed for a detailed characterization of ultrashort acoustic pulses generated by femtosecond laser pulses in hybrid goldcobalt bilayer structures [7]. In order to investigate the ultrafast pathways of energy transport and conversion in these structures under femtosecond laser irradiation we have performed time-resolved pump-probe measurements. A set of hybrid multilayer samples composed of (111) gold layers with different thicknesses on top of a 30 nm-thin hcp-cobalt film deposited on a (0001) sapphire substrate has been manufactured by magnetron sputtering. Femtosecond p-polarized optical pump pulses (duration 100 fs, =800 nm, pulse repetition rate 500 kHz) were focused at the gold-air interface at oblique incidence (Fig. 1a). A weak time-delayed s-polarized ultrashort probe pulse (duration 100 fs, =400 nm) was used to record the dynamics of pump–induced reflectivity changes at the gold-air interface (Fig. 1b). At zero pump-probe delay time a strong electronic peak caused by free carrier absorption of pump photons in gold was observed in all investigated samples. Hot electrons excited in gold within the optical skin depth (13 nm) of pump light 6 propagate across the sample at a velocity of the order of the Fermi velocity in gold, i.e. 1.4x10 km/s [1]. After crossing the gold layer hot electrons release their excess energy in the cobalt layer, where the electron-phonon coupling is much stronger and the electron mean free path much shorter than in gold. The transient temperature increase in cobalt is estimated to be at least one magnitude larger than in gold. Afterwards the thermal expansion of the cobalt layer generates an ultrashort compressional acoustic pulse propagating in both directions, into the sapphire and into the gold layer. The acoustic propagation in a (111) gold layer occurs at a speed of 3.45 km/s suggesting that the strain pulse should arrive at gold-air interface after the delay time of d/cs. Figure 1b shows the acoustic echo in a sample with d=70 nm delayed by d/cs~20 ps. More physical insight can be gained from the detailed analysis of the acoustic echoes. Ultrafast acousto-plasmonic [6,7] and optical reflectivity measurements [8] demonstrated that optical techniques can be particularly useful to reconstruct the acoustic pulses with spatial extension smaller than the skin depth of probe radiation. In this case the time-derivative of the optical signal gives the pulse shape. For example, the time-derivative of the acoustic echo in the inset of Fig. 1b shows the bell-shaped acoustic pulse with the duration of 2 picoseconds. Taking into account that the speed of sound in hcp-cobalt is (Co) roughly 6 km/s, it gives the heat penetration depth in cobalt of cobalt= accs =12 nm. This value is in excellent agreement with the theoretically estimated length of hot electrons diffusion in cobalt and with most recent experimental observations [7]. We have observed the acoustic echoes in all investigated samples with d ranging from 70 to 270 nm. The acoustic pulse shape remained unchanged but strain amplitude decreased significantly. The dependence of strain amplitude on gold thickness in Fig. 1c shows an exponential decay with a decay length of 120 nm. The most recent theoretical investigation shows that the shapes of experimentally observed ultrashort electron pulses in gold [1] can be explained within the frame work of wave-diffusion theory [9]. The ballistic front is followed by the diffusive tail, which carries most of the pulse energy. Therefore the exponential decay of the acoustic amplitude with gold thickness can be adequately described by the conventional theory for hot electron diffusion in metals leading to the decay length of about 100-150 nm [3,4]. From the physical point of view this is a characteristic length of hot electrons diffusion in gold during the time of electron-phonon relaxation.


To summarize, using time-resolved pump-probe measurements we have observed the generation of ultrashort acoustic pulses in cobalt heated by ultrashort electron pulses excited in gold. These measurements provide 120 nm and 12 nm electronic heat diffusion lengths in gold and in cobalt, respectively. Given the case that illuminating the gold surface with circularly polarized light leads to the emission of partially spin-polarized photoelectrons [10], it remains completely unclear how long spin polarization can be carried by ultrashort electron pulses, a question crucial for applications in ultrafast spintronics [5]. References [1] S.D. Brosnon, J.G, Fujimoto and E.P. Ippen, Phys. Rev. Lett. 59 (1987) 1962. [2] G. Tas and H.J. Maris, Phys. Rev. B 49 (1994) 15046. [3] V.E. Gusev and O.B. Wright, Phys. Rev. B 85 (1998) 2878. [4] O. B. Wright and V. E. Gusev, IEEE Trans. UFFC 42 (1995) 331. [5] A. Melnikov et al., Phys. Rev. Lett. 107 (2011) 076601. [6] V.V. Temnov, Nature Photonics 6 (2012) 728. [7] V.V. Temnov et al., Nature Communications 4 (2013). [8] K.J. Manke et al., AIP Conference Proceedings 1506 (2012) 22. [9] S. Kaltenborn et al., Phys. Rev. B 85 (2012) 235101. [10] D. Pescia and F. Meier, J. Appl. Phys. 53 (1982) 2035.

Figures

Fig. 1: (a) Schematic drawing of the femtosecond pump-probe experiment: hot electrons optically generated at the gold-air interface propagate through the layer of gold and heat up a 30 nm thin cobalt layer, resulting into generation of an ultrashort acoustic pulse. The red shaded area illustrates the distribution of lattice temperature in the gold/cobalt structure after electron-phonon relaxation (approximately 1 picosecond after pump excitation). The dashed curve shows the exponential decay of pump intensity within the skin depth. (b) Pump-probe reflectivity signal for a 70 nm thin gold layer. The inset shows the time-derivative of a time-delayed acoustic echo, which gives the acoustic pulse shape with a duration of 2 ps (see ref. [6,7] for details). (c) The exponential dependence of the acoustic strain amplitude on gold thickness.


Oxazine and rhodamine confined into nanosized latex particles. A successful strategy to increase the energy transfer efficiency and to develop improved red-edge emitting dyes.

1

1

2

3

2

Iñigo López Arbeloa , Jorge Bañuelos , Luis Cerdán , Eduardo Enciso , Ángel Costela , and 2 Inmaculada García-Moreno 1

Facultad de Ciencia y Tecnología, Universidad del País Vasco/EHU, Apdo. 644, 48080, Bilbao, Spain. Instituto de Química Física “Rocasolano”, CSIC-Consejo Superior de Investigaciones Científicas, Serrano 119, 28006, Madrid, Spain. 3 Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Av. Complutense s/n, 28040, Madrid, Spain. 2

inigo.lopezarbeloa@ehu.es Abstract The development of tunable dye lasers working in the red part of the visible or the near infrared (>650 nm) is a very active area or research due to the advantages, which offer these devices in many fields; such as, biomedicine or biophotonic. For instance, the long wavelength light can penetrate deeper into tissues. However, most of the red dyes reported in the bibliography have two main drawbacks: low absorption at the standard pump wavelength and poor photostability. One approach to overcome these problems is to excite the red-emitting dye from a donor dye, characterized by high photostability, via a non-radiative Förster resonance energy transfer (FRET). Such mechanism requires good overlap between donor emission and acceptor absorption bands and depends strongly on the distance between donor and acceptor molecules, which usually demands high concentrations. One way to ensure the proximity of the dye molecules and ameliorate the efficiency of the energy transfer 1

process is enclosing the donor and acceptor molecules within solid host of nanometric size (Figure 1).

H N

O

H N

COOEt

N

O

NH2

N

Figure 1. Rhodamine G and Nile Blue encapsulation into latex nanoparticles. Recently, we confirmed that the photophysical and lasing properties Rhodamine 6G (Rh6G) confined into polymeric nanoparticles (latexes) and homogeneously dispersed in aqueous suspensions are 2

further enhanced. On the basis of these promising results, we decided to use this system for the FRET device. To this aim, we chosen Nile Blue (NB) as energy acceptor since its spectra overlap with the energy donor rhodamine is high enough to ensure improved energy transfer efficiencies (Figure 1). The absorption spectra confirm the presence of the two chromophores into the latex framework, without signs of aggregation, regardless of the dye-loading of the nanoparticles. The fluorescence and excitation spectra confirm the presence of the FRET process (Figure 2). Indeed, bright red-emission


from the NB is detected upon excitation of the donor rhodamine. Accordingly, the fluorescence from the xanthene is quenched by the FRET process, as is reflected in the faster fluorescence decay in the 3

donor region. Compared with donor/acceptor physical mixtures in solutions, with the same Rh6G and NB proportions used in the latex measurements, the FRET efficiency is greatly ameliorated owing to the dye encapsulation, which imply closer donor-acceptor distances. The energy migration enables that the FRET process happens at longer distances. As result, efficient and photostable laser emission is recorded for the NB, pumping at the Rh6G. Work in progress is carried to modulate the FRET efficiency by changing the donor/acceptor ratio or the size of the nanoparticle.

Figure 2. Fluorescence emission at different times after excitation upon excitation at the Rh6G in aqueous suspensions of latex doped with Rh6G and NB.

References [1] J. P. S. Farinha, J. M. G. Martinho, J. Phys. Chem. C, 112, (2008) 10591. [2] V. Martín, J. Bañuelos, E. Enciso, I. López Arbeloa, A. Costela, I. García-Moreno, J. Phys. Chem. C, 115 (2011) 3926. [3] L. Cerdán, E. Enciso, V. Martín, J. Bañuelos, I. López Arbeloa, A. Costela, I. García Moreno, Nature Photonics, 6 (2012) 621.


The cross density of states near a plasmonic surface: An analytical approach in the electrostatic limit including radiative corrections. Laura Rosales-Zárate1, Miztli Yépez1,2, Francisco J. García-Vidal1,3 and Juan José Sáenz1,2 1

Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain. 2 Departamento de Física de la Materia Condensada and Instituto “Nicolás Cabrera”, Universidad Autónoma de Madrid. 28049 Madrid, Spain. 3 Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid. 28049 Madrid, Spain. laura.rosales@uam.es Abstract: The concept of cross density of states (CDOS) characterizes the intrinsic spatial coherence of complex photonic or plasmonic systems, independently of the illumination conditions [1]. The CDOS, proportional to the imaginary part of the Green's function connecting two different points, appears as a fundamental quantity in a large number of situations: from determining superradiance and energy transfer between two emitters [2] to high-resolution tomography from ambient seismic noise [3], just to mention a few. Although the calculation of Green's functions can be performed numerically, simple analytical expressions are often required to gain physical insight and optimize computational approaches. Here we propose a simple analytical extension of the electrostatic approximation [4] based on the radiative corrections usually applied in scattering from small particles [5]. The approximation, that fulfills the optical theorem in absence of absorption, is compared with exact results for both dielectric and plasmonic surfaces. Acknowledgements: This work was supported by the Spanish Ministerio de Ciencia e Innovación through grant: Consolider NanoLight (CSD2007-00046), as well as by the Comunidad de Madrid (Microseres-CM, S2009/TIC-1476). M.Y. thanks the Mexican Consejo Nacional de Ciencia y Tecnología for a postdoctoral grant. References [1] Cazé, A., Pierrat, R., and Carminati, R., Phys. Rev. Lett. 110, 063903 (2013). [2] Martín-Cano, D., Martín-Moreno, L., García-Vidal, F. J., and Moreno, E. Nano Letters, 10, 31293134. (2010). [3] Shapiro, N., Campillo, M., Stehly, L., and Ritzwoller, M. Science 307, 1612-1615 (2005). [4] Panasyuk, G. Y., Schotland, J. C., and Markel, V. A., J. Phys. A: Math. Theor., 42, 5203 (2009). [5] Albaladejo, et al., Opt. Express, 18, 3556–3567 (2010).


Reconstruction of acoustic pulses for gold-cobalt bilayer structures probed with femtosecond surface plasmons 1

2

2

2

Viktor Shalagatskyi , Denys Makarov , Luyang Han , Oliver G. Schmidt and Vasily V. Temnov 1

1

Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Université du Maine, 72085 Le Mans cedex, France. 2 Institute for Integrative Nanosciences, IFW Dresden, 01069 Dresden, Germany viktor.shalagatskyi.etu@univ-lemans.fr

Abstract Fundamental interactions induced by lattice vibrations on ultrafast time scales have become increasingly important for modern nanoscience and technology. Experimental access to the physical properties of acoustic phonons in the terahertz frequency range and over the entire Brillouin zone is crucial for understanding electric and thermal transport in solids and their compounds. Among different metal-based compounds the hybrid metal-ferromagnet multilayer structures attract particular interest because of their applications in ultrafast spintronics [1,2] and magneto-plasmonics [3,4], with most previous studies devoted to their electronic properties. Here we extend these studies to investigate ultrafast coherent phonon pulses and report on the generation and nonlinear propagation of giant (displacement in the order of 1% of the lattice constant) acoustic strain pulses in hybrid gold/cobalt bilayer structures, monitored with ultrafast surface plasmon interferometry [5]. This new technique is presented in Fig. 1. It allows for unambiguous characterization of arbitrary ultrafast acoustic transients. A hybrid acousto-plasmonic 120 nm gold/35 nm cobalt/ sapphire multilayer structure was manufactured by magnetron sputtering of a (111)-oriented gold layer on top of an hcp-cobalt film deposited on a (0001) sapphire substrate. The ferromagnetic cobalt layer was excited through the substrate by an ultrashort optical pump pulse and served as an efficient opto-acoustic transducer. Due to a very short electronic mean free path the diffusion of hot electrons in cobalt is particularly inefficient and the heat penetration depth only slightly exceeds the 10 nm skin depth of the pump radiation (at 400 nm optical wavelength). Thermal expansion of the cobalt transducer launches a unipolar acoustic pulse in both directions. This compressional acoustic strain pulse η(z,t) creates a layer of higher ion density which moves at sound velocity cs=3.45 km/s in gold. As the stationary charge separation between electrons and ions in a metal is prohibited by the tiny Debye radius, the spatial profile of the electron charge density exactly follows the ionic one. Therefore, an ultrashort acoustic pulse creates a time-dependent spatial profile of the dielectric function inside the metal, which modulates the surface plasmon wave vector ksp, when the strain pulse arrives within the surface plasmon skin depth δskin=13 nm at the goldair interface. We will show how to reconstruct the acoustic strain from the plasmonic pumb-probe measurements resolving the Fredholm integral equation, which describe the changing of dielectric permittivity due to action of the acoustic strain. Normally, this equation can be presented as follows:

δε ! (t ) =

εm ∞ ∫ η (t!) exp (− t − t! / τ skin ) sgn (t − t!) dt! τ skin −∞

(1)

After taking the Fourier transform it is easy to express the equation for strain: T ( w) =

F[δε ! (t )] τ skin τ 2 1+ τ 2skin w 2 = F[δε ! (t )] skin ε m F[exp (− t − t! / τ skin ) sgn (t − t!)] εm iw

(2)

Finally to get the acoustic strain profile from the measurements the thermal background should be removed and only after that the expression (2) can be used, where δε ! (t ) stands for experimental data. This methodic was used to process the data from the set-up explained above with only difference in the thickness of gold layer which 100 nm bigger. Simple approach to use the Fourier transform shows great results and high conformity with theoretical calculations (Fig. 1 (e)). Therefore this “in-click reconstruction” method can be used as good approach for reconstruction of acousto-plasmonics measurements without need to fit the data manually. References [1] S.D. Brosnon, J.G, Fujimoto and E.P. Ippen, “Femtosecond Electronic Heat-Transport Dynamics in Thin Gold Films,” Phys. Rev. Lett. 59, 1962-1965 (1987).


[2] G. Tas and H.J. Maris, “Electron diffusion in metals studied by picosecond ultrasonics,” Phys. Rev. B 49, 15046-15054 (1994). [3] K J. Chau, M. Johnson and A.Y. Elezzabi, “Electron-Spin-Dependent Terahertz Light Transport in Spintronic-Plasmonic Media,” Phys. Rev. Lett. 98, 133901 (2007). [4] A. Melnikov et al., “Ultrafast Transport of Laser-Excited Spin-Polarized Carriers in Au/Fe/MgO(001),” Phys. Rev. Lett. 107, 076601 (2011). [5] V.V. Temnov et al., “Active magneto-plasmonics in hybrid metal-ferromagnet multilayer structures,” Nature Photonics 4, 107-110 (2010). [6] V.V. Temnov, “Ultrafast acousto-magneto-plasmonics,” Nature Photonics 6, 728-736 (2012). [7] V.V. Temnov et al., “Femtosecond nonlinear ultrasonics in gold probed with ultrashort surface plasmons”, Nature Communications 4, doi:10.1038/ncomms2480 (2013). [8] K.J. Manke et al., “Detection of Shorter-Than-Skin-Depth Acoustic Pulses in a Metal Film via Transient Reflectivity’”, in AIP Conference Proceedings 1506, 22-27, doi:10.1063/1.4772519 (2012). Figures

Fig. 1: (a) Schematic drawing of the acousto-plasmonic pump-probe experiment: surface plasmons propagating at the gold-air interface, probe the reflection of acoustic pulses generated in laser-heated cobalt transducer. (b) Ultrafast dynamics of the real (red line) and imaginary (blue line) parts of the surface dielectric function extracted from plasmonic interferograms with fit of thermal background (dashed lines). (c) Superposition of reconstructed (blue line) and calculated theoretically (red line) strains with pulse duration about 3 nm (FWHM). (d) Reconstructed strain profile using the Fourier approach showing all echoes delayed in time with inset explaining the obtained results.


Statistical scattering properties of disordered waveguides: closed channels contributions and the effective medium approximation M. Yépez and J. J. Sáenz Condensed Matter Physics Department and Centro de Investigación en Física de la Materia Condensada (IFIMAC), Universidad Autónoma de Madrid, Fco. Tomás y Valiente 7, 28049-Madrid, Spain miztli.yepez@uam.es Abstract. The statistical scattering properties of disordered waveguides are studied by using a disordered system of length L, that we call the “Building Block”. The Building Block is constructed as a sequence of n scattering units in the propagation direction, which are statistically independent and identically distributed. Each scattering unit is idealized as delta potential in the longitudinal direction of the waveguide, while the transverse profile is a random function. The theoretical study is developed by using two perturbative approaches: Born series method and the transition matrix method. Both perturbative approaches consider weak scattering units and their results are obtained in the short-wave-length or weak disorder approximation, where the wave number k and the mean free path ` satisfy the condition k`  1. The theoretical predictions are compared with numerical simulations when the waveguide supports N = 2 open channels (traveling modes) and N 0 = 0, 1, 2, 3 closed channels (evanescent modes) were considered in the calculations. Born series method predicts that the closed channels contributions are crucial for the statistics of the scattering amplitudes, while the statistic of the corresponding coefficients is insensitive to those contributions. Unfortunately, this Born series method is only valid in the ballistic regime (L  `), where its predictions are in good agreement with the numerical simulations; however, Born series predictions suggest that the closed channels contributions are relevant for the scattering amplitudes even beyond the ballistic regime, what is confirmed by the numerical simulations: see Fig. 1. In order to give a more general description than Born series method, a perturbative method based on the transition matrix T method was performed. This method explains the intriguing contributions of the closed channels in the statistics of the scattering amplitudes, considers explicitly the multiple scattering processes and gives an excellent agreement with the numerical simulations even beyond the ballistic regime: see Fig. 2. In addition, when the waveguide admits a very large number of open channels N  1, the transition matrix method predicts that the Building Block can be replaced by an “effective potential”. On the other hand, if the number of open channels is N ∼ 1, it is not possible to approximated the Building Block by an effective medium, what is due to the contributions coming form the recurrent multiple scattering. Keywords: Disordered waveguides; Quantum transport; Random processes PACS: 72.80.Ng,73.23.-b,73.23.Ad,42.25.Dd

REFERENCES [1] A. Ishimaru, Propagation and Scattering in Random Media, Academic Press, New York, 1978. [2] P. Sheng, Introduction to Wave Scattering, Localization and Mesoscopic Phenomena, Academic Press, New York, 1995.


[3] P. A. Mello and N. Kumar, Quantum Transport in Mesoscopic Systems. Complexity and Statistical Fluctuations, Oxford University Press, Oxford, 2004. [4] L. S. Froufe-Pérez, M. Yépez, P. A. Mello and J. J. Sáenz, Phys. Rev. E, 75, 031113, (2007); M. Yépez, P. A. Mello and J. J. Sáenz, AIP. Conf. Proc., 1319, 49, (2010). [5] U. Frisch, Annales d’Astrophysique, 30, 565, (1967). [6] Ben Payne, Tom Mahler and Alexey G. Yamilov, Waves in Random and Complex Media, 23, 43, (2013).

FIGURES 1

0 0

-0.01

(Born)

Im〈t22〉

0.1

Im〈r22〉

(Num)

Im〈t22〉

0 c)

Num N’=3 Born N’=3

〈T12〉

0.1 (Born)

〈T12〉

0.4

2 1.5 1 (Num) 0.5 〈g〉 0 0 0.5 L/l 1

(Num)

〈T22〉

0 0.4

〈T12〉 N’=0 N’=1 N’=2 N’=3

(Num)

〈R11〉

(Num)

0.8 L/l

1.2 0

0.4

0.8 L/l

0

1.2

〈R22〉

0.2

(Born)

〈R11〉

1.5

(Num)

0.2 b)

(Num) 0.25 〈R11〉

0.6 0.4

-0.02

d) (Num)

0 0

(Num)

(Num)

〈T11〉

0.8

〈Taa 〉

Im〈r22〉

(Born)

0

0.2

b)

〈Raa 〉

a)

〈g〉

a)

0 0

〈R12〉 0.5

(Num)

1

L/l

1.5

Left: Born series and numerical results for the expectation values of scattering amplitudes and coefficients when the waveguide supports N = 2 open channels and N 0 = 3 closed channels were considered in the calculations. FIGURE 1.

1

Re〈t22〉

0.8 0.6

a)

Theory Simulations 1 N’=3 N’=0 N’=1 0.8 N’=2 0.6 N’=3

(Num)

Re〈t22〉

Re〈r22〉

a)

0.4 0.2 0 0

0.4 0.2

0.4

0

L/l 0.8

-0.02

0.25

0.05 0 0

Theory Simulations N’=3 N’=0 N’=1 N’=2 N’=3

0.5

1

1.5

0.1 0 0

2 L/l 2.5

Im〈r22〉

Im〈t22〉

0.2 0.15 0.1

b)

0.2 (Num)

Im〈t22〉

0.4 L/l 0.8 3

3.5

1.2

4

4.5

Simulations N’=0 N’=1

N’=3

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-0.01

1.2

b)

Theory

0

0 -0.01 -0.02 0

(Num)

0.4

Re〈r22〉 1.2 L/l 0.8

0 -0.01 -0.02 0

0.5

L/l

1

1.5

Theoretical and numerical results for the scattering amplitudes when the wave guide supports N = 2 open channels and N 0 = 3 closed channels were considered in the calculations. FIGURE 2.


Optimized refractive index of subwavelength spheres for maximum scattering cross-section and zero backwards scattering Yan Zhang1, M. Nieto-Vesperinas2 and J.J. Sáenz1 1. Departamento de Física de la Materia Condensada and Centro de Investigación en Física de la Materia Condensada (IFIMAC), Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain. 2. Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas CSIC, Campus de Cantoblanco, 28049 Madrid, Spain. Email: gmemome@gmail.com

Zero backward scattering from dielectric spherical particles had been theoretically predicted by Kerker et.al.1 decades ago. The first experimental confirmations of Kerker’s proposal concerning unconventional forward–backward scattering asymmetry have been reported very recently2-4. Nowadays, particles showing zero backscattering with large scattering cross section in forward direction are catching great attention of scientists in various fields due to their unique properties, such as the efficiency enhancement as light diffusing elements in solar cells. As we will show, there is an optimal particle refractive index at which, the scattering cross section of a single sphere is maximum. The motivation of this work is that from the theoretical point of view, we find the best materials of spherical particles for having large forward diffusion without backward scattering of light. Magnitude of backscattering is defined by the backscattering efficiency materials having

5

. For

at several different wavelength λ, we choose always the one

corresponding to larger extinction cross section

. And turns out such wavelength

position is also where the first Kerker condition of the particle occurs. Notice that calculations are done under assumption of the absence of absorption within the entire calculated spectrum of wavelength, i.e. parameter (

=

. As a result, we find out that when size

) is about 2.75, spherical particles with m = 2.47 have zero

backscattering and the largest scattering cross section

under the first Kerker

condition. The examples of non-absorbing materials given in this work are diamond, titanium dioxide (TiO2) and strontium titanate (SrTiO3). The extinction and scattering


cross-section of Si particles are also calculated, as an example of materials with absorption in the regime of visible light. And it is demonstrated that the main Mie resonances within the calculated light spectrum are attributed to the electric and magnetic dipoles.

References: [1]. M. Kerker, D. Wang, and G. Giles, J. Opt. Soc. Am., 73 (1983) 765. [2]. J.M. Geffrin, B. García-Cámara, R. Gómez-Medina, P. Albella, L.S. Froufe-Pérez, C. Eyraud, A. Litman, R. Vaillon, F. González, M. Nieto-Vesperinas, J. J. Sáenz, and F. Moreno, Nat. Commun. 3 (2012) 1171. [3]. S. Person, M. Jain, Z. Lapin, J.J. Sáenz, G. Wicks, and L. Novotny, Nano Lett., DOI: 10.1021/nl4005018 (2013). [4]. Y.H. Fu, A.I. Kuznetsov, A.E. Miroshnichenko, Y.F. Yu, and B. Luk’yanchuk, Nat. Commun. 4 (2013) 1527. [5]. C. F. Bohren, and D. R. Huffman, Absorption and Scattering of Light by Small Particles (John Wiley and Sons) (1983).

Figure 1. Extinction cross-section as a function of the refractive index. The total extinction cross-section of different materials is plotted at constant size parameter 2.75. The 3-dimentional differential scattering images of three selected data points a, b, and c are also shown. The projection of the yz-plane of points a, b, and c is shown in the inset d.


Sheet resistance of multi-layer stacking of silicene P. Capiod,1 M. Berthe,1 A. Resta,2 P. De Padova,3 P. Vogt4, G. Le Lay,2 B. Grandidier1 1

Institut d’Electronique et de Microélectronique et de Nanotechnologies, IEMN, (CNRS, UMR 8520), Département ISEN, 41 bd Vauban, 59046 Lille Cédex, France 2 Aix-Marseille University, CINaM-CNRS, Campus de Luminy, Case 913, 13288 Marseille Cedex 9, France 3 Instituto di Struttura della Materia, Consiglio Nazionale delle Ricerche -ISM, via Fosso del Cavaliere, 00133 Roma, Italy 4 Technische Universität Berlin, Institut für Festkörperphysik Hardenbergstr.36 10623 Berlin, Germany pierre.capiod@isen.fr Abstract During the year 2012, several groups have demonstrated that honeycomb lattices of silicon could be 1,2,3 synthesized by epitaxial growth of silicon on the Ag(111) surface. The observation of a conical band dispersion provided convincing evidences for the existence of a sheet of silicene with graphene-like 1 properties. Remarkably, the Fermi velocity measured from the photoemission data was found to be 6 1.3x10 m/s, slightly higher than in graphene. Such a result holds good promise to reach high electron mobility in silicene sheets, pleading for experimental studies of silicene transport properties. Here, we will first describe the formation of silicene multilayers on top of an initial silicene layer grown 4 on the Ag(111) substrate. Based on Low Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM) experiments, we will report on the LEED pattern and STM structure of the multilayers, that readily differ from the initial layer (Figure 1). The latter layer acts as a wetting layer, that enables the pilling up of the subsequent silicene layers into islands, consistent with a StranskiKrastanov growth mode. To perform transport measurements of the silicene sheets, we have then used a multiple probe STM combined with scanning electron microscopy. STM tips were positioned on micrometer-scale areas that were free of step bunches caused by the underlying Ag substrate and fully covered with islands of silicene multilayers. Since the contact formation between the probe and the silicene multilayers can modify the interlayer spacing and thus the electronic coupling of the multilayers with the Ag surface, an analysis of the conductance variation as a function of the tip displacement was performed. Based on this analysis, we will show that transport measurements can be acquired with a van der Pauw arrangement to determine the sheet resistance of silicene multilayers. References [1] P. Vogt, P. De Padova, C. Quaresima, E. Frantzeskakis, M. C. Asensio, A. Resta, B. Ealet, G. Le Lay, Phys. Rev. Lett. 108 (2012) 155501. [2] C.-L. Lin, R. Arafune, K. Kawahara, N. Tsukahara, E. Minamitani, Y. Kim, M. Kawai, Applied Physics Express 5 (2012) 045802. [3] L. Chen, C.-C. Liu, B. Feng, X. He, P. Cheng, Z. Ding, S. Meng, Y. Yao, K. Wu, Phys. Rev. Lett. 109 (2012) 056804. [4] P. Vogt, P. De Padova, T. Bruhn, A. Resta and G. Le Lay, submitted


Figures

Figure 1. (a) the LEED pattern performed at 51eV, showing silver interger order spots, silicene integer order spots and (1/3,1/3) type superstructure spots of the (√3x√3)R30° silicene phase (from black to white). (b) STM image with the silicene √3x√3 multi-layers recorded at 0.7V and 100pA.


Integration of Atomic Force Microscopy with Optical Microscopy and Spectroscopy Pavel Dorozhkin, Artyom Shelaev, Alexey Shchokin, Mikhail Yanul, Victor Bykov NT-MDT Co., Build. 100, Zelenograd Moscow, 124482 Russia, dorozhkin@ntmdt.com

We will demonstrate capabilities of Atomic Force Microscopy integrated with various optical microscopy and spectroscopy techniques: Confocal Raman/Fluorescence/Rayleigh microscopy, Scanning Near-field Optical Microscopy (SNOM, a-SNOM, s-SNOM), Tip Enhanced Raman Microscopy and others. AFM and optical techniques provide complimentary information about sample structure, its physical and chemical properties. Results will be demonstrated for various types of samples: polymer blends, pharmaceutical tablets, graphene, nanowires and nanotubes, solar cells, silicon devices, hard disk drives etc. Tip Enhanced Raman Scattering (TERS) is the technique utilizing a special AFM probe (nano-antenna) to localize light at the nanometer scale area near the probe apex. When scanning the sample with respect to the probe, the obtained optical (Raman or fluorescence) maps have lateral resolution which is not limited by the light diffraction. TERS and other tip assisted optical techniques (tip enhanced fluorescence, scattering SNOM etc.) will be discussed. The successful TERS results achieved due to deep integration of AFM with confocal Raman microscopy will be demonstrated – with lateral resolution down to 15 nm.

Figure. (Upper left) universal integration of AFM with light: “4Pi” optical access to AFM tip. (Upper right) principle of tip assisted optical techniques (Tip Enhanced Raman Scattering and others). (Bottom) Comprehensive AFM-Raman characterization of polymer blend

 


Inelastic electron tunneling spectroscopy simulations of single-molecule junctions with covalent Au-C contacts Giuseppe Foti,1, 2,* Hector Vázquez,3 Daniel Sánchez-Portal,1, 2 Andrés Arnau,1, 2, 4 and Thomas Frederiksen2, 5 1

Centro de Física de Materiales, Centro Mixto CSIC-UPV, Paseo Manuel de Lardizabal 5, Donostia-San Sebastián, Spain 2 Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, Donostia-San Sebastián, Spain 3 Department of Chemistry, University of Warwick, Gibbet Hill, Coventry, CV4 7AL. 4 Depto. de Física de Materiales UPV/EHU, Facultad de Química, Apdo. 1072, Donostia-San Sebastián, Spain 5 IKERBASQUE, Basque Foundation for Science, E-48011, Bilbao, Spain *giuseppe_foti@ehu.es

Abstract Alkane chains ending with thiols or amines have been always considered a benchmark systems for studies in the field of molecular electronics [1, 2] since they can be easily functionalized and they form stable and well defined contact to gold electrodes. More recently very high conductance values have been experimentally achieved starting from trimethyl tin (SnMe 3)-terminated molecules [3, 4]. In general, one of the main tasks once the junction is physically realized is to verify the real compositional structure of the molecular junction. Recently Cheng et al. [4] demonstrated that trimethyl tin-functionalized alkanes, after loosing the Sn-(CH 3)3 group, can form a direct Au-C bond with the metallic surface. In that condition it was possible to achieve a conductance about 100 times larger than analogous alkane based molecular junctions with other anchoring groups. Here we propose an additional way to verify experimentally the nature of metal/molecule bonding. Inelastic Electron Tunneling Spectroscopy (IETS) allows a unique compositional and structural characterization of nanojunctions since it gives the vibrational fingerprint of molecular adsorbates. So, comparing the IETS of (SnMe 3)-terminated chains and that one of alkane directly bonded to gold surface could allow an unambiguous characterization of metal/molecule bonding since the two molecules give qualitatively different spectra. We performed first principles calculation of the IETS of (SnMe 2)-terminated hexane (C6Sn) and of the same molecule but directly bonded to the gold surface through a covalent Au-C bond (C6Au) and for different electrodes separations in a regime of elastic deformation. In Fig. 1 a) and b) are shown the C6Au and C6Sn geometries respectively in the less stretched configurations. Structural relaxation of all geometries was done with the DFT code Siesta [5] while for the calculation of phonon modes and IETS the Inelastica package [6, 7] was used. For both kind of molecules the IETS present the typical peaks of alkane chains. Nevertheless, in the case of (SnMe2)-terminated hexane, at low energies the CH3 groups give a strong inelastic signal which is not present in the case of the pure hexane chain with direct Au-C bond [Fig. 1 c)]. This peak allows to easily distinguish the two types of molecule and verify the presence of a direct bond of alkane with gold surface. References [1] Y. Kim, T. J. Hellmuth, M. Burkle, F. Pauly, and E. Scheer, ACS Nano, 5 (2011) 4104. [2] J. Zhou, C. Guo, and B. Xu, Journal of Physics: Condensed Matter, 16 (2012) 164209. [3] W. Chen, J. R. Widawsky, H. Vázquez, S. T. Schneeabeli, M. S. Hybertsen, R. Breslow, and L. Venkataraman, Journal of the American Chemical Society, 43 (2012) 17160. [4] Z.-L. Cheng, R. Skouta, H. Vazquez, J. R. Widawsky, S. Schneebeli, W. Chen, M. S. Hybertsen, R. Breslow, and L. Venkataraman, Nat Nano, 6 (2011) 353. [5] J. M. Soler, E. Artacho, J. D. Gale, A. García, J. Junquera, P. Ordejón and D. Sánchez-Portal, Journal of Physics: Condensed Matter 11, 2745 (2002). [6] T. Frederiksen, M. Paulsson, M. Brandbyge, and A.-P. Jauho, Phys. Rev. B, 20 205413 (2007). [7] http://sourceforge.net/projects/inelastica.


Figures

Figure 1 a) C6Au and b) C6Sn geometries in the less stretched configuration. In c) is shown the low energy part of the IETS for the two geometries. Thick line represents the signal at negative bias. At 90 meV the methyl groups give a strong signal (red curve) which is not present in the case of C6Au.


Disclosing fine frictional details dependent on the supramolecular order of polymorphic self-assembled monolayer Markos Paradinas,a Carmen Munuera,aǂ Christophe Silien,b§ Manfred Buckb and Carmen Ocala a Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), 08193-Bellaterra, Spain EaStCHEM School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, KY169ST, UK ǂ present address: Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Cantoblanco 28049 Madrid, Spain § present address: Department of Physics and Energy, and Materials and Surface Science, University of Limerick, Ireland b

mparadinas@icmab.es Abstract

Micro-/nanoelectromechanical systems demand robust ultrathin films or lubrication. As they can drastically modify the frictional properties of surfaces, few nanometers thick self-assembled monolayers (SAMs) constitute accepted candidates as boundary lubricants. Their high stability and easy preparation make them attractive also for low cost applications. Given their high order, organosulfur SAMs have been archetypal systems for structural investigations, but few efforts have been devoted to analyze the influence of lateral inhomogeneities on their surface properties. In this work, the impact on the frictional response of the surface due to the existence of crystalline domains with lateral dimension in the submicrometer range is considered. To this end, two polymorphic structures of SAMs of ω-(4'-methylbiphenyl-4-yl) butane-1-thiol (BP4) coexisting on Au(111) are investigated by friction force microscopy technique (FFM). FFM is ideally suited for non-invasive friction studies since forces can be measured with high sensitivity and different types (e.g. local normal force and lateral force) can be monitored simultaneously. However, FFM measurements can provide even more detailed information, for example, on non-isotropic packing of molecules or molecular tilt in the SAMs. Described by rectangular 5√3 6√3

3 (α-phase) and oblique

2√3 (β-phase) unit cells, the two polymorphic structures of the BP4 SAM exhibit pronouncedly

different frictional responses. The lateral nano-tribological heterogeneity of the surface is further influenced by the azimuthal orientation dependence of friction for each phase. These details can be revealed by friction anisotropy and friction asymmetry both of which are related to the dependence of the mechanical response on the sliding direction. In particular, this phenomenon is exploited in the less densely packed -phase for which the separate analysis of forward and backward lateral force scans is used to differentiate domains rotated 180º. The results presented in this work demonstrate the level of structural control required in the design of SAMs for nano-tribology applications.

References

[1] M. Paradinas, C. Munuera, C. Silien, M. Buck, C. Ocal, Phys. Chem. Chem. Phys. 15 (2013)  1302. 


Figures

In figure (a) the tip forward and backward scan over different BP4 β-phase crystalline domains is represented and superimposed to the experimental friction map. The friction (F) is defined as the half of the difference between lateral force forward and backward signals. The corresponding lateral force signals are schematically represented in (b). While F(1) â&#x2030; F(2) is a clear signature of friction anisotropy related to molecular domains with different azimuthal orientation (proved by the corresponding molecular periodicity images (c and d) obtained in each location), there are also regions which exhibit the same friction values (i.e., F(1) = F(3)) but a shift in the lateral force signals, indicating the same tipsurface sliding relationship, in other words (1) and (3) are domains rotated by 180°.


Electron scattering in the presence of spin-orbit interaction: the S. Schirone,

1,2

1

1

1,3,4

G. Peschel, R. Piquerel, P. Gambardella,

surface alloy A. Mugarza

1

1

Catalan Institute of Nanotecnology (ICN), UAB Campus, E-08193 Bellaterra, Spain Dipartimento di Fisica, Università di Roma “La Sapienza”, P.le Aldo Moro 2, 00185 Roma, Italy 3 Instituciò Catalana de Recerca i Estudis Avancats (ICREA), E-08193 Barcelona, Spain 4 Departament de Física, UAB Campus, E-08193 Barcelona, Spain

2

stefano.schirone@icn.cat

Abstract Spin-orbit interaction (SOI) in metallic surfaces can lead, via the Rashba effect, to a splitting of the spin degeneracy and the emergence of particular spin textures where the latter appears correlated with the wave vector k. The consequent entanglement between spin and orbit leads to the suppression of backscattering, which can give rise to exotic transport phenomena such as the induction of dissipationless charge and spin currents [1,2]. Here we use the BiAg2 alloy, which is characterized by the strongest to date Rashba effect [3,4], to study the effect of SOI on scattering. The alloy is formed on the the deposition of

monolayer of Bismuth, which induces a (√

√ )

(

) surface after

reconstruction. The

scattering has been studied using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS). In this way we have studied electron confinement by measuring the interference patterns formed by surface electrons scattered from monoatomic steps. The negligible leakage we observe across the steps indicate a strong confinement effect, comparable to that observed in metals with marginal SOI such as Ag(111) [5]. This is in agreement with the quantized energy levels measured for electrons confined between a pair of steps, comparable to that of infinite quantum wells. Surprisingly, confinement is strong even at energy regions where backscattering is predicted to be prohibited by the spin texture of the electronic states, and where previous STM studies failed to observe interference patterns [6]. Additionally, the effect of the atomic structure of the scatterer has been explored by using two different types of step, where substantial differences have been found both in the scattering strength and asymmetry of the step potential. The latter indicates that, for particular step configurations, scattering is significantly different for electrons going upwards or downwards across the steps. The results describe a scenario that is far more complex than that of a simple two dimensional free-electron gas in the presence of a strong SOC.

Reference

[1]

D. Pesin and A. H. MacDonald, Nature Materials 11, 409 (2012).

[2]

M. Franz, Nature 466, 323 (2010).


[3]

C. Ast, J. Henk, A. Ernst, L. Moreschini, M. C. Falub, D. Pacile, P. Bruno, K. Kern, and M. Grioni, Physical Review Letters 98, 186807 (2007).

[4]

G. Bihlmayer, S. BlĂźgel, and E. V Chulkov, Physical Review B 75, 195414 (2007).

[5]

J. E. Ortega, J. Lobo-Checa, G. Peschel, S. Schirone, Z. M. Abd-El-Fattah, M. Matena, F. Schiller, P. Borghetti, P. Gambardella, and A. Mugarza, Submitted 1 (2013).

[6]

H. Hirayama, Y. Aoki, and C. Kato, Physical Review Letters 107, 027204 (2011).

Figures

Step B

Step A

Step B

Step A

Figure 1: (a) Topographic image of a zone of the sample with different type of monoatomical step, acquired with and . Image size: â &#x201E; -map acquired acquired at . (b) . Note that the intensity of the standing wave scattered from the two kind of steps is different. (c) Topographic image performed with . Image size: . The surface lattice structure is resolved in the image, and the different termination of each step type can be distinguished. (d) Schematics of the lattice of the surface alloy. Solid lines indicate the direction of each step type.


Successful Synthesis of Nest-like Nanoporous ZnO Films by Pulsed Laser Deposition a

b

b

Abdullah Al-Dwayyan , Joselito Labis , Mahmoud Hezam Fahad Alharbi a

Physics and Astronomy Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia b

King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2454, Riyadh 11451, Saudi Arabia Contact Email: dwayyan@ksu.edu.sa

Abstract We report on the growth of high quality nest-like nanoporous ZnO films on FTO substrates. The nestlike ZnO films were grown by pulsed laser deposition technique under an oxygen pressure background. Prior to the growth, deposition of a very thin seed layer of ZnO on the substrate showed to be essential in determination of the final morphology of the film. Effect of different growth parameters on the morphology and structure of the films have been investigated. SEM observation of the films showed that they are denser than previously reported films with similar morphology [1-3], which makes them very promising as photoanodes in dye-sensitized solar cells.

References 1. E. Hosono, S. Fujihara, I. Honma, H. S. Zhou, Adv. Mater. 2005, 17, 2091. 2. E. Hosono, S. Fujihara, T. Kimura, H. Imai, J. Colloid Interface Sci. 2004, 272, 391. 3. K. Kakiuchi, M. Saito, S. Fujihara, Thin Solid Films 2008, 516, 2026.


“Pulsed-Electrochemical Deposition of Fe-based nanoparticles from non-aqueous media: effect of different additives on morphology development” 1

1

Marya Baloch , Sofia Perez-Villar , Carmen M. Lopez

1, *

1

CIC Energigune, Parque Tecnológico de Álava Albert Einstein 48, 01005 Miñano, Álava, Spain E-mail: clopez@cicenergigune.com mbaloch@cicenergigune.com

Abstract Iron based-nanoparticles have a range of technologically-important applications which encompass diverse areas such as battery materials, photo- and electro-catalysis, environmental 1 remediation, and as catalysts for the growth of nanostructured carbons. The performance of iron-based nanoparticles on all of these applications depends strongly on their morphology (size, shape, distribution and orientation of particles), and their chemical composition. Therefore, developing synthetic methods that allow for the systematic control of these properties is a subject of intense scrutiny. In this study we investigate the effects of additives during pulsed-electrochemical deposition (ECD) of iron-based nanoparticles from formamide/FeCl2 solutions. ECD is a useful method to produce inorganic materials because it is a soft-solution synthesis in which the plating media can be easily adjusted to obtain electrodeposits with systematically-controlled 2 morphologies. Electrodeposition of Fe-based materials has been widely studied previously, 3 however, most of the experiments done so far had been performed in aqueous media. Nonaqueous plating media, like the one described in this work, offers wider potential and temperature windows for ECD, together with more complex and richer chemistry. This translates into more opportunities to tune the morphology and composition of inorganic nanoparticles. To study the impact of additives on the morphology and composition of iron particles, we have chosen two general categories of additives, classified according to: (i) chemical 2+ interaction with the active cation, Fe , (coordinating or chelating additives) or (b) surface interactions with growing iron nuclei (surfactants and polymers). Carboxylic acids such as citric 2+ acid had been demonstrated to quench the oxidation of ferrous (Fe ) ions in aqueous media, 3 although their role in non-aqueous media had not been deeply studied yet. Figure 1 shows an example of our own experiments using (a) FeCl2/formamide solution, and (b) FeCl2/formamide with citric acid additive, during pulsed-ECD. The corresponding current profiles are shown in (c) and (d), respectively. This figure shows a clear change in the particle size and distribution when using citric acid, which is also reflected in the shape of the current profiles and the variation of current densities. Finally, the effects of various additives and the correlation between the chemistry of the plating media and the morphology of the electrodeposits will be discussed. The plating media and the electrodeposited nanoparticles had been characterized, by ultraviolet-visible (UV-vis), and Fourier Transform-Infrared-Attenuated Total Reflectance (FTIR-ATR) spectroscopy, Scanning Electron (SEM) and Optical Microscopies, by the analysis of current profiles, and voltammetric methods. References 1. (a) Liu, H.; Wexler, D.; Wang, G., “One-pot facile synthesis of iron oxide nanowires as high capacity anode materials for lithium ion batteries.” Journal of Alloys and Compounds 487 (1–2), (2009) L24-L27; (b) Tibbetts, G. G.; Devour, M. G.; Rodda, E. J., “An adsorptiondiffusion isotherm and its application to the growth of carbon filaments on iron catalyst


particles.” Carbon 25 (3), (1987) 367-375; (c) Xi, Y.; Megharaj, M.; Naidu, R., “Dispersion of zerovalent iron nanoparticles onto bentonites and use of these catalysts for orange II decolourisation.” Applied Clay Science 53 (4), (2011) 716-722; (d) Prasek, J.; Drbohlavova, J.; Chomoucka, J.; Hubalek, J.; Jasek, O.; Adam, V.; Kizek, R., “Methods for carbon nanotubes synthesis-review.” Journal of Materials Chemistry 21 (40), (2011) 15872-15884. 2. (a) López, C. M.; Choi, K.-S., “Electrochemical Synthesis of Dendritic Zinc Films Composed of Systematically Varying Motif Crystals.”, Langmuir 22 (25), (2006) 1062510629; (b) Choi, K.-S., “Shape control of inorganic materials via electrodeposition.” Dalton Transactions 40 (2008) 5432-5438. 3. Electrodeposition of Iron and Iron Alloys, in Modern Electroplating, Fifth Edition, Eds. M. Schlesinger and M. Paunovic, 2010 John Wiley & Sons, Inc.

Figures (a)

(b)

(c)

(d)

Figure 1: The relationship between morphology and current profile of pulsed-electrodeposited iron-based nanoparticles. SEM images of electrodeposits from: (a) 0.03M FeCl2/formamide solution, (b) 0.03M FeCl2/formamide with citric acid additive; the inserts in each panel show typical average particle size and aggregation patterns. Current profiles of the plating solutions used, (c) full profile and (d) amplification of a single pulse: (d-i) without additive (red line) and, (d-ii) with additive (blue line).


Solar Cell Diagnostics by Combination of Kelvin Force Microscopy with Local Photoexitation A. Ankudinov1, P. Dorozhkin2, A. Shelaev2 1

Ioffe Physical-Technical Institute of the Russian Academy of Science National Research University of Information Technologies, Mechanics and Optics 2

NT-MDT Co., Build. 100, Zelenograd Moscow, 124482 Russia e-mail: alexander.ankudinov@mail.ioffe.ru

The modern high-efficiency multijunction solar cell (MJ SC) consists of three subcells based on semiconductor nanoheterostructures. This study using atomic force, Kelvin probe force and confocal microscopy demonstrates that the operation of each subcell could be monitored. The combination of methods used allowed measurement of the surface potential variations at the cross-section of multijunction solar cell as a function of the wavelength and the beam position of a laser excitation source focused into a ~400 nm spot. The experimental surface photovoltage profiles obtained are in good agreement with results of the qualitative simulation. This agreement is very important. Although the photoexcitation applied was significantly higher than operating photoexcitation, inside the structure no parasitic barriers were found that could lower the efficiency of the studied solar cells.

FIGURE. (a) Schematic of layers in an MJ SC. The three p-n junctions are shown by arrows. (b) Schematic of experiment. Optical micrographs of the edge of the cleaved surface of a SC during a KPFM experiment under focused photoexcitation of (c) the p-n junction in Ge with a blue laser (473 nm) and (d) p-n junction in GaAs with a red laser (785 nm). Latin numerals designate: (I) Ge substrate, (II) III-V layers (GaAs and GaInP ), (III) free space,and (IV) KPFM cantilever.


FIGURE. Comparison of experimental and simulated data. (a-c) Photoexcitation with laser light (473 nm) focused on the p-n junctions in (a) Ge, (b) GaAs, and (c) GaInP . (d-f) Photoexcitation with laser light (785 nm) focused on the p-n junctions in (d) Ge, (e) GaAs, and (f ) GaInP . Designations: SPV, experimental surface photovoltage profile. A simulated profile is also given above each plot. Below, under all the plots are shown schematics of layers in MJ SCs.


Growth of Raspberry-like and Sphere-like TiO2 Nanostructures by Controlled Agglomeration of TiO2 Nanocrystals Mahmoud Hezama, Ahmad Eltonia, Joselito Labisa, Bader AlRuhaimib, Mohammad AlDuraibib, Abdullah Aldwayyanb a

King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2454, Riyadh 11451, Saudi Arabia

b

Physics and Astronomy Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia

Contact Email: mhezam@ksu.edu.sa Abstract TiO2 single crystals of 10-15 nm size were synthesized using a one-pot solvothermal chemical reaction. Controlled agglomeration of the nanocrystals could be achieved to produce nanospheres and raspberry-like TiO2 nanostructures with different sizes (50-200 nm) and with good monodispersion. X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and N2 adsorption-desorption isotherms measurements were carried out for the grown nanostructures. Results on dye-sensitized solar cells fabricated using the grown nanostructures of different sizes and shapes will also be presented.


Renaissance Initial Training Network- Innovative Polyelectrolytes for energy and environment M贸nica Moreno, David Mecerreyes POLYMAT, University of the Basque Country (UPV/EHU), Joxe Mari Korta Center, Avda. Tolosa 72, 20018 Donostia-San Sebastian, Spain monica.moreno@ehu.es Abstract RENAISSANCE ITN is a multidisciplinary and intersectorial European research and training network in innovative polymers for a sustainable society. The six academic partners of the network and the three industrial participants will carry out a join programme including research projects, PhDs, master courses, supervision and mentoring, specific local courses, as well as network-wide activities such as secondments, local courses open to the network participants, four workshops, one summer school and one conference. The main goal of RENAISSANCE initial training network will be to improve the career perspective of researchers by training them at the forefront of research in the field of innovative polyelectrolytes for applications in energy and environment technologies. The training objectives of RENAISSANCE ITN are addressed to prepare the ESR and ERs in subject matters related to the most recent advancements in the research on polyelectrolyte technologies. These scientists will be ready to apply polymer methodologies for industrial research in various fields of applications (e.g. Energy, Environment) and to satisfy the knowledge requirements for a more sustainable economy.

Figure 1. Academic and Industrial partners that take part in the network.

Acknowledgments This Project has received funding from the European Union (Renaissance FP7-PEOPLE-2011-ITN).


Silver nanowires for transparent conductive electrodes: In situ mechanical characterization Boris Polyakov1,3, Sergei Vlassov2,3, Leonid Dorogin2,3, Mikk Antsov2,3, Ilmar Kink2,3, Runno Lohmus2,3 1

Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063, Riga, Latvia 2 Institute of Physics, University of Tartu, Riia 142, 51014, Tartu, Estonia 3 Estonian Nanotechnology Competence Centre, Riia 142, 51014, Tartu, Estonia boris.polyakov@cfi.lu.lv

Abstract Recently, flexible and stretchable electronics based on nanomaterials have received much recent attention as an alternative of transparent conducive oxide coatings for wide range of applications, including thin film solar cells, displays, organic light-emitting diodes, etc. Two dimensional networks of metal nanowires (NWs) can form a high-performance transparent conducting film that could be coated by different methods from a liquid solvent, and significantly reduce production costs. For example, solution-coated films of silver NWs have a transmittance and sheet resistance close to ITO [1]. There are several works, where mechanical properties of silver NWs were investigated, such as micro hardness, Young modulus, tensile strength in axial stretching and three point bending tests [2, 3, 4]. However, to the best of our knowledge, pure bending tests of Ag NWs were not reported in literature yet. In this work, we describe bending tests inside a SEM chamber, which enables the measurement of the Young modulus and yield strength of NWs, and monitor elastic and plastic deformation in real time. Silver NW half-suspended on edge of micro machined silicon grating was pushed by AFM tip glued to a quartz tuning fork (QTF) mounted on a nanomanipulator (fig.1). The NW-tip force interaction detected by a QTF force sensor and corresponding to the visualized by SEM NWâ&#x20AC;&#x2122;s bending was used to calculate Young modulus and yield strength, similar experimental setup used in [5]. Bending tests were performed on 20 NWs with diameters ranging from 76 nm to 211 nm. Typically two regions were clearly distinguished on bending curves as shown on fig. 2. In initial region (a-b) NW bends elastically and the force grows linearly with a bending angle of NW. It was also confirmed separately on several NWs that in the linear region removal of external force will cause NW to return in initial no deformed state (elastic deformation regime). At certain point deformation turns to plastic. The onset of elastic-to-plastic transition can be detected precisely from the change of slope of the force curve (point b). From this point bending continues with a nearly constant force (region b-c) corresponding to plastic yield of the wire. Some NWs demonstrated slightly different behavior during bending test due to crack formation (fig. 3). Formation of crack inside NW manifests itself as clear steps on force curve. In some cases crack stabilizes and stops propagating, in other cases NWs break completely. We found Young modulus of Ag NWs was 90Âą29 GPa. Additionally, fatigue tests with several millions of cycles were performed and it was demonstrated that Ag NWs have high fatigue resistance and can be bent elastically multiple times to significant curvatures without failure. References [1] L. Hu , H. Wu , Y. Cui, Metal nanogrids, nanowires, and nanofibers for transparent electrodes. MRS Bulletin 36 (2011) 760-765 [2] X. Li, H. Gao, C. Murphy, K. Caswell,Nanoindentation of Silver Nanowires. Nanolett. 3 (2003) 14951498 [3] Y. Zhu, Q. Qin, F. Xu, F. Fan, Y. Ding, T. Zhang, B.Wiley, Z. Wang. Size effects on elasticity, yielding, and fracture of silver nanowires: In situ experiments. Phys. Rev. B 85 (2012) 045443 [4] B. Wu, A. Heidelberg, J. Boland, J. Sader, X. Sun, Y. Li, Microstructure-Hardened Silver Nanowires. Nanolett. 6 (2006) 468-472 [5] B.Polyakov, L.Dorogin, S.Vlassov, M.Antsov, P.Kulis, I.Kink, R. Lohmus. In situ measurements of ultimate bending strength of CuO and ZnO nanowires. Europ. Phys. J. B. 85 (2012) 366


Figures

Figure 1. Schematics of experiment setup inside SEM. AFM tip glued on QTF pushes a silver NW on silicon grating.

Figure 2. Bending test of Ag NW. Set of four SEM images and corresponding force registered simultaneously by force sensor. Tip approaches a NW (a). Maximal elastic deformation of NW (b). Plastic deformation regime (c). Retraction of the tip (d). Force curve of NW deformation (e).

Figure 3. SEM images of plastically deformed Ag NWs. Bend without cracking (a). Cracked during bending (b).


Successful Growth of TiO2 nanosheets with {001} facets for Dye-Sensitized Solar Cells a

b

b

c

Saif Qaid , Mahmoud Hezam , Joselito Labis , Idriss M. Bedja Abdullah Al-Dwayyan a

Physics and Astronomy Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia b

c

a

King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2454, Riyadh 11451, Saudi Arabia

CRC, Department of Optometry, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433, Saudi Arabia Contact Email: 431106475@student.ksu.edu.sa

Abstract The growth of nanocrystals with exposed high energy facets has a particular significance due to the high reactivity of these facets. In this work, we report a fast hydrothermal synthesis of high-quality single crystals TiO2 nanosheets with the highly reactive {001} facets as the top and bottom dominating facets. X-Ray Diffraction (XRD) showed that the grown nanosheets have the typical anatase structure. Scanning Electron Microscopy and Transmission Electron Microscopy showed that the grown nanosheets have average area of about 50-60 nm. Selected area electron diffraction (SAED) patterns of the nanosheets confirmed that the {001} are the exposed facets. Dye-sensitized solar cells (DSSCs) fabricated using the grown nanosheets will be discussed in this work, and a comparison with the commercial Degussa P25 TiO2 nanoparticles will be presented.


Fast Responsive Photochromic Materials 1

1,2

1

Nuria-Alexandra Vázquez-Mera , Claudio Roscini , Jordi Hernando , Daniel Ruiz-Molina

2

1

Departament de Química, Universitat Autònoma de Barcelona (UAB), 08193, Cerdanyola del Vallès, Spain 2 Centro de Investigación en Nanociencia y Nanotecnología (CIN2-CSIC), 08193, Cerdanyola del Vallès, Spain nuria.vazquez@cin2.es

Abstract During the last decades photochromic compounds have been proposed for a number of applications in optics, electronics, computing and materials science.

[1]

Among them, the manufacturing of

photoprotective coatings (e.g. for ophthalmic lenses and smart windows) is currently their main [2]

commercial use. For this application, photochromic compounds must fulfill several requirements: (i) to display light-induced conversion from a colorless to a colored state, (ii) to revert back thermally to the [1]

initial situation in absence of irradiation (T-type photochromicity ), and (iii) to present fast color darkening and fading kinetics. Although a number of T-type organic photochromes displaying such properties have been developed, to achieve high switching speeds in solid materials still remains a [3]

challenge. This is due to the effect of the supporting matrix where these compounds are loaded, which imposes steric restrictions to the significant molecular motions typically involved in the interconversion [1a,3]

between the two states of the photochromes.

As a result, the thermal back-reaction rate of these

compunds is largely slowed down with respect to solution, thus affecting the performance or even preventing the application of the final photochromic materials. In an attempt to overcome this drawback, herein we report on a novel, straightforward and universal methodology to attain high photochromic switching speeds in rigid matrices. Our approach consists in photochrome encapsulation into liquid-filled solid-shell hollow capsules, thus obtaining a solid material with solution-like photochromic behavior that will be preserved even when subsequently embedded into rigid hosts. Moreover, our strategy does not require synthetic modification of commercially available photochromes, while it also tackles other severe problems encountered when directly dispersing photochromic molecules within solid matrices, such as dye aggregation and migration. With this aim, we have synthesized polyamide capsules containing photochromic solutions by interfacial polymerization in oil-in-water emulsions.

[4]

In particular, the polycondensation of terphthaloyl chloride

with diethylenetriamine was carried out, which led to the formation of polymeric shells around the microsized droplets of the organic solvent phase where the photochromes of interest had been previously dissolved. Measurements of the thermal color fading kinetics of the resulting capsules showed monoexponential decays and rapid decoloration rates that resemble those obtained for the same photochromic compounds in solution, and are at least ten-fold faster than those measured for rigid polymer thin films and solid particles. In addition, by properly selecting the nature of the liquid core, the capsules prepared were found to display high stability both in time and upon redispersion in a variety of solvents, facilitating their subsequent processing for the fabrication of functional materials


where fast photochromic response is required, such as photoprotective coatings and optical data processing devices.

References [1] a) H. Dürr, H. Bouas-Laurent, Photochromism: Molecules and Systems, Elsevier, 1st ed. (2003). b) M. Irie, Chem Rev., 100 (2000) 1683. [2] S. N. Corns, S. M. Partington, A. D. Towns, Color. Technol., 125 (2009) 249. [3] R. A. Evans, T. L. Hanley, M. A. Skidmore, T. P. Davis, G. K. Such, L. H. Yee, G. E. Ball, D. A. Lewis, Nature Mater., 4 (2005) 249. [4] S. J. Pastine, D. Okawa, A. Zettl, J. M. J. Fréchet, J. Am. Chem. Soc., 131 (2009) 13586.

Figures

Figure 1. a) SEM image of polyamide capsules containing a photochromic solution of 1,3-dihydro-1,3,3trimethylspiroindoline-2,3’-(3H)-naph(2,1-b)-(1,4)oxazine (Photorome I). b) Thermal decoloration kinetics of photochromic polyamide capsules, photochromic polystyrene thin film (PS-film) and photochromic polystyrene nanoparticles (PS-Nps).


Design of Novel Hierarchical TiO2 Photoanode Material for Optimum Performance in DyeSensitized Solar Cell M. Zukalová1, L. Kavan1, A. Zukal1, and M. Graetzel2 1

J. Heyrovsky Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejskova 3, CZ-18223 Prague 8, Czech Republic 2 Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland marketa.zukalova@jh-inst.cas.cz

Abstract The dye-sensitized solar cell (DSC, Graetzel cell) presents an attractive alternative to solid-state photovoltaics at competitive cost[1]. Morphological engineering of a TiO2 photoanode aims at preparation of perfectly crystalline transparent layers with high surface area and represents one of the key issues in optimization of DSCs. Due to obvious incompatibility of these properties, combined hierarchical layers were designed to meet both requirements. The solar performance of multilayer mesoporous TiO2 films sensitized with N-945 dye scales linearly for 1 – 3 layer films, but reaches plateau value for more than 8 layers[2, 3]. The solar conversion efficiency of 5.05 % was found for a 2.3 μm thick mesoporous TiO2 film consisting of 10 layers[4]. To eliminate problem of electron capturing and recombination with dye/electrolyte within extremely open mesoporous structure, which probably hinders the increase of solar conversion efficiency for 8 and more mesoporous TiO2 layers, electrospun nanocrystalline fibrous TiO2 was incorporated into mesoporous TiO2 thin film. TiO2 with fibrous morphology was found to be beneficial for the performance of corresponding photoanode in dyesensitized solar cell (DSC). Obviously, its wirelike structure suitably interconnects mesoporous network and thus increases the electron collection efficiency from the TiO2 layer to the F-doped SnO2 (FTO) electrode. Performance of the DSC with 2.5 µm bimodal TiO2 photoanode reached 5.35%. Among others, the performances of DSCs are limited by the charge recombination taking place mainly at the FTO/TiO2 interface. Due to the porous structure of TiO2 films the electrolyte solution easy penetrates to the FTO. The physical contact between the electrolyte and the FTO surface causes the charge recombination resulting in a considerable loss of photoelectron conversion efficiency in DSCs. Therefore, the recapture of the photoinjected electrons with the I3– ions should be avoided. FTO coverage with a thin compact TiO2 underlayer was found to be the effective way to reduce the contact surface area for the bare FTO substrate and the redox electrolyte (so-called blocking effect). Besides the blocking effect, the compact layer can improve the adhesion of the FTO/TiO2 interface as well and creates more electron pathways from the porous layer to FTO and subsequently increases the electron transfer efficiency. Compact non-porous TiO2 films were prepared by means of dip-coating from precursor sol containing poly(hexafluorobutyl methacrylate) as the structure directing agent[5]. The roughness factor is lower than 20 even for approximately 1 m thick film. Films were grown on glass and FTO and cover even rough surfaces of the substrates perfectly, which proves the presence of thixotropic properties in the Ti-precursor gel. Acknowledgement: Financial support of GA CR (P108/12/0814) is acknowledged. Reference List [1]

B. O'Regan, M. Grätzel, Nature 353 (1991) 737-740.

[2]

M. Zukalova, A. Zukal, L. Kavan, M.K. Nazeeruddin, P. Liska, M. Gratzel, Nano Letters 5 (2005) 1789-1792.

[3]

M. Zukalova, J. Prochazka, A. Zukal, J.H. Yum, L. Kavan, Inorganica Chimica Acta 361 (2008) 656-662.

[4]

M. Zukalova, J. Prochazka, A. Zukal, J.H. Yum, L. Kavan, M. Graetzel, Journal of the Electrochemical Society 157 (2010) H99-H103.

[5]

J. Prochazka, L. Kavan, M. Zukalova, P. Janda, J. Jirkovsky, Z.V. Zivcova, A. Poruba, M. Bedu, M. Döbbelin, R. Tena-Zaera, Journal of Materials Research (2013) DOI: 10.1557/jmr.2012.240.


magineNano Abstract Booklet Poster Contributions (part II)  

Bilbao (Spain) hosted the 2nd edition of the largest European Event in Nanoscience & Nanotechnology, ImagineNano, from the 23rd until the 26...

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