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Imaging and Manipulation of Adsorbates using Dynamic Force Microscopy

AtMol International Workshop 2013 April 16-17 Nottingham - UK


2013 AtMol International Workshop April 16-17, 2013 Nottingham-UK

[IMAGING AND MANIPULATION OF ADSORBATES USING DYNAMIC FORCE MICROSCOPY]


Index

page

Foreword

5

Scientific Program

7

Abstracts

13


IMAGING AND MANIPULATION OF ADSORBATES USING DYNAMIC FORCE MICROSCOPY AtMol International Workshop Nottingham-UK April 16-17, 2013

Dynamic force microscopy (also known as non-contact atomic force microscopy) has evolved rapidly over the past decade to become an extremely powerful technique capable of not only ultrahigh resolution imaging and spectroscopy, but the precise positioning of individual adsorbed atoms and molecules. This workshop will focus on the latest advances in the manipulation of condensed matter using dynamic force microscopes, bringing together experimentalists and theorists working on the precise control of adsorbates on a variety of substrates.

Sponsors

Organisers:     

Antonio Correia (Phantoms Foundation, Spain) Sebastien Gauthier (CEMES/CNRS, France) Christian Joachim (CEMES/CNRS, France) Philip Moriarty (University of Nottingham, UK) Adam Sweetman (University of Nottingham, UK)

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[SCIENTIFIC PROGRAM]


Scientific Program Tuesday, April 16, 2013

Imaging and Manipulation of Adsorbates using DFM 09:15-10:00 Registration and Coffee

10:00-10:15

10:15-10:45 10:45-11:15

11:15-11:45

11:45-12:15

12:15-12:45

12:45 -14:15

14:15-14:45

14:45-15:15

15:15-15:45

Welcome and Overview, Philip Moriarty (University of Nottingham, UK) Clemens Barth (CINAM, France) "Metal clusters on alkali halide surfaces: Characterization and Manipulation"

p. 17

Tea/Coffee Sebastien Gauthier (CEMES/CNRS, France) "NC-AFM and KPFM study of the adsorption of triphenylene derivatives on KBr(001)" Thilo Glatzel (University of Basel, Switzerland) "Imaging and directed rotation of single molecules by non-contact force microscopy" Pavel Jelinek (Institute of Physics of the ASCR, Czech Republic) "Advance characterization of nanostructures using nc-AFM/STM measurements"

p. 19

p. 21

p. 23

Lunch Stefan Tautz (Forschungszentrum Juelich GmbH, Germany) "Molecules in the transport path: The mechanical properties of STM junctions “in contact"" Philipp Rahe (The University of Utah, USA) "Benzoic acids on calcite: From templated assembly to on-surface synthesis" Nikolaj Moll (IBM Research, Switzerland) "Imaging Atoms and Bonds by Atomic Force Microscopy"

p. 43

p. 33

p. 29

AtMol International Workshop 2013, Nottingham-UK

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15:45-16:15

16:15-16:45

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Tea/Coffee Ruben Perez (Universidad Aut贸noma de Madrid, Spain) " Water and metal adsorbates on reducible oxide surfaces: Can theory help to understand the AFM and KPFM contrast?"

AtMol International Workshop 2013, Nottingham-UK

p. 31


Scientific Program Wednesday, April 17, 2013

Imaging and Manipulation of Adsorbates using DFM

10:00-10:30

Jascha Repp (Universitaet Regensburg, Germany) "Dynamic Force Imaging and Spectroscopy of Individual Molecules on Thin Insulating Films"

p. 35

10:30-11:00

Bartosz Such (Instytut Fizyki UJ, Poland) "Isolated dangling bonds on H:Ge(001) surface"

p. 37

11:00-11:30

Tea/Coffee

11:30-12:00

Yoshiaki Sugimoto (Osaka University, Japan) "Mechanical atom manipulation using atomic force microscopy at room temperature"

p. 39

12:00-12:30

Adam Sweetman (University of Nottingham, UK) "Understanding molecular interactions using NC-AFM: can we move 'beyond' imaging?"

p. 41

12:30-14:00

14:00-14:30

14:30-15:00

Lunch Lev Kantorovich (King’s College London, UK) "Intricate Mechanism of Lateral and Vertical Manipulation of Super-Cu Atoms on the Cu:O Surface: Experiment and Theory" Markus Ternes (Max Planck Institut, Germany) "Investigation of the mechanical properties of a monoatomic layer by combined STM and AFM measurements"

p. 25

p. 45

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15:00-15:30

15:30-16:00

16:00

12

Matt Watkins (London Centre for Nanotechnology, UK) "Developing realistic models of interfaces from simulation" Robert Linder (Johannes GutenbergUniversit채t Mainz, Germany) "Photoactivated Covalent Bonding of Organic Molecules on an Insulator Surface" Tour of Nottingham Nanoscience group labs

AtMol International Workshop 2013, Nottingham-UK

p. 47

p. 27


[ABSTRACTS]


Abstracts (Alphabetical Order)

page

Clemens Barth (CINAM, France) "Metal clusters on alkali halide surfaces: Characterization and manipulation"

17

Sebastien Gauthier (CEMES/CNRS, France) "NC-AFM and KPFM study of the adsorption of triphenylene derivatives on KBr(001)"

19

Thilo Glatzel (University of Basel, Switzerland) "Imaging and directed rotation of single molecules by non-contact force microscopy"

21

Pavel Jelinek (Institute of Physics of the ASCR, Czech Republic) "Advance characterization of nanostructures using nc-AFM/STM measurements"

23

Lev Kantorovich (King’s College London, UK) "Intricate Mechanism of Lateral and Vertical Manipulation of Super-Cu Atoms on the Cu:O Surface: Experiment and Theory"

25

Robert Linder (Johannes Gutenberg-Universität Mainz, Germany) "Photoactivated Covalent Bonding of Organic Molecules on an Insulator Surface"

27

Nikolaj Moll (IBM Research, Switzerland) "Imaging Atoms and Bonds by Atomic Force Microscopy"

29

Ruben Perez (UAM, Spain) "Water and metal adsorbates on reducible oxide surfaces: Can theory help to understand the AFM and KPFM contrast?"

31

Philipp Rahe (The University of Utah, USA) "Benzoic acids on calcite: From templated assembly to on-surface synthesis"

33

Jascha Repp (Universitaet Regensburg, Germany) "Dynamic Force Imaging and Spectroscopy of Individual Molecules on Thin Insulating Films"

35

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Bartosz Such (Instytut Fizyki UJ, Poland) "Isolated dangling bonds on H:Ge(001) surface"

37

Yoshiaki Sugimoto (Osaka University, Japan) "Mechanical atom manipulation using atomic force microscopy at room temperature"

39

Adam Sweetman (University of Nottingham, UK) "Understanding molecular interactions using NCAFM: can we move 'beyond' imaging?"

41

Stefan Tautz (Forschungszentrum Juelich GmbH, Germany) "Molecules in the transport path: The mechanical properties of STM junctions “in contact""

43

Markus Ternes (Max Planck Institut, Germany) "Investigation of the mechanical properties of a monoatomic layer by combined STM and AFM measurements"

45

Matt Watkins (London Centre for Nanotechnology, UK) "Developing realistic models of interfaces from simulation"

47

AtMol International Workshop 2013, Nottingham-UK


Metal clusters on alkali halide surfaces: Characterization and manipulation

Clemens Barth CINaM-CNRS, Aix-Marseille University, Campus de Luminy, Case 913, 13288 Marseille Cedex 09, France barth@cinam.univ-mrs.fr

Interest in studying metal clusters of nanometer size has increased rapidly in the last decade, particularly due to the discovery of their surprising chemical activity when adsorbed on insulating substrates [1]. Important properties like adsorption site, growth, morphology and charge state of individual clusters can be characterized by noncontact AFM (nc-AFM) and Kelvin probe force microscopy (KPFM) [2]. A very important aspect is the lateral manipulation of clusters on surfaces, which permits studying the properties of clusters as a function of surface site. In recent years we have been dealing with metal clusters on the (001) surfaces of bulk alkali halide crystals and studied their properties and manipulation characteristics by nc-AFM and KPFM in ultra-high vacuum (UHV). - Alkali halide surfaces are standard insulating model surfaces since they exhibit stoichiometric, almost defect-free and large atomically flat terraces providing easy access for both microscopy techniques. In particular, such model surfaces are perfect for characterizing supported molecules and metal nanoclusters. A large benefit of using alkali halide material is that it can be doped with divalent metal impurity ions like Mg2+ or Cd2+, which leads to nanostructured (001) surfaces [3] permitting adsorption studies of molecules and clusters in dependence on surface site [4].

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At the beginning of the presentation, the properties of the clean alkali halide surfaces and supported metal clusters will be briefly summarized. It will be then shown that gold clusters of nanometer size can be indeed manipulated on the surface by the AFM tip [5]. The most important characteristics of the manipulation are discussed and the manipulation mechanisms involved will be explained. At the end, an outlook is given that focuses on future applications in the manipulation of clusters. New potential substrates like thin films or nanostructured alkali halide surfaces [3] and new measurements protocols will be discussed. References: [1] Nanocatalysis, edited by U. Heiz and U. Landman (Springer Verlag, Berlin, 2007) [2] C. Barth, A. S. Foster, C. R. Henry and A. L. Shluger, Adv. Mater 23, 477 (2011) [3] C. Barth and C. R. Henry, Phys. Rev. Lett. 100 (2008) 096101 C. Barth and C. R. Henry, New J. Phys. 11, 043003 (2009) [4] C. Barth, M. Gingras, A. S. Foster, A. Gulans, G. FĂŠlix, T. Hynninen, R. Peresutti and C. R. Henry, Adv. Mater. 13 (2012) 2061 [5] T. Hynninen, G. Cabailh, A. S. Foster and C. Barth, accepted for Scientific Reports (2013)

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NC-AFM and KPFM study of the adsorption of triphenylene derivatives on KBr(001)

A. Hinaut, A. Pujol, F. Chaumeton, D. Martrou, A. Gourdon and S. Gauthier1 1

CNRS, CEMES (Centre d'Elaboration des MatĂŠriaux et d'Etudes Structurales), BP 94347, 29 rue Jeanne Marvig, F-31055 Toulouse, France

We have started a program aimed at imaging single molecules on the surface of a bulk insulator at room temperature. This task is essential to the goal of connecting a molecule to metallic electrodes in a planar geometry to build a single molecular device [1]. One of the major difficulties in this task is to immobilize the molecules on the surface of the sample. The diffusion barrier of most molecules on usual insulating surfaces is generally quite low making room temperature diffusion too fast for imaging. In this study KBr(001) was chosen as a substrate for its ease of preparation and the relative facility for atomic resolved imaging. On this substrate, the moleculesurface interaction is usually dominated by electrostatic forces. Our approach consists in equipping a flat, aromatic triphenylene molecular core with different peripheral polar groups, as shown in the figure.

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The adsorption of two of these molecules was studied in detail: R=CH3 (Hexamethoxytriphenylene: HMTP [2]) and R=propyl-CN (2,3,6,7,10,11Hexacyanopropyl-oxytriphenylene: HCPTP [3]). Kelvin probe measurements were performed on HCPTP. These results will be discussed with a special emphasis on low coverage measurements at low coverage where what we interpret as small aggregates of molecules or even single molecules adsorbed on a defect could be manipulated. References: [1] Multiple atomic scale solid surface interconnects for atom circuits and molecule logic gates, Joachim, C;. Martrou, D.; Rezeq, M.; Troadec, C.; Jie, D.; Chandrasekhar, N.; Gauthier, S. J. Phys.: Condens. Matter 2010, 22, 084025 [2] NC-AFM study of the adsorption of hexamethoxytriphenylene on KBr(001) A. Hinaut, K. Lekhal, G. Aivazian, S. BataillÊ, A. Gourdon, D. Martrou and S. Gauthier, J. Phys. Chem. C, 115(27), 13338-13342 (2011) [3] A NC-AFM and KPFM study of the adsorption of a triphenylene derivative on KBr(001), A. Hinaut, A. Pujol, F. Chaumeton, D. Martrou, A. Gourdon, S. Gauthier, Beilstein J. Nanotechnol. 2012, 3, 221–229

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Imaging and directed rotation of single molecules by non-contact force microscopy

E. Meyer1, R. Pawlak1, S. Kawai1, S. Fremy1 , B. Such2, L.A. Fendt3, H. Fang3, F.Diederich3, T. Trevethan4, A.L. Shluger4, C.H.M. Amijs5, P. de Mendoza5, A.M. Echavarren5, and T. Glatzel1 1

Department of Physics, University of Basel, Switzerland Centre for Nanometer-Scale Science and Advanced Materials (NANOSAM), Jagiellonian University, Krakow, Poland 3 Department of Chemistry and Appliede Biosciences, ETHZ, Z端rich, Switzerland 4 Department of Physics and Astronomy, University College London, UK 5 Institute of Chemical Research of Catalonia (ICIQ), Tarragona, Spain 2

Non-contact force microscopy has demonstrated true atomic resolution on metals, semiconductors and insulators. The application of AFM to single molecules is a challenge because of relatively weak bonding to the substrate, which often leads to high diffusion rates of the molecules. We will present molecules, which were designed to interact with specific sites on insulating surfaces. Molecular wires of porphyrin molecules on ionic crystal surfaces are observed [1,2]. A complete immobilization at kink sites of KBr(001) is observed for single truxene molecules at room temperature [3]. Recently, intramolecular resolution is studied on a variety of molecules [4]. A further challenge is the manipulation of molecules on surfaces, including the controlled rotation, which means that the direction of rotation of the molecule can be chosen by the experimentalist [5]. The control of the probing tip is of central importance for a quantitative understanding of nc-AFM imaging and force spectroscopy. Progress has been made by a variety of preparation procedures: sputtering, indentation or pick-up of molecules, such as CO. The attachment of a single molecule to the end of the tip is shown for the case of a functionalized porphyrin, which can used as a stable probing tip for imaging in the attractive as well as the repulsive regime.

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References: [1] Th. Glatzel, L. Zimmerli, S. Koch, S. Kawai, E. Meyer, Molecular assemblies grown between metallic contacts on insulating surfaces, Appl. Phys. Lett., 94, (2009), 3 [2] Th. Glatzel, L. Zimmerli, S. Kawai, E. Meyer, L.-A. Fendt and F. Diederich, Oriented growth of porphyrin-based molecular wires on ionic crystals analysed by nc-AFM , Beilstein J. Nanotechnol. 2, 34-39, (2011)., 2, (2011), 34-39 [3] B. Such, T. Trevethan, Th. Glatzel, S. Kawai, L. Zimmerli, E. Meyer, A. L. Shluger, C. H. M. Amijs, P. de Mendoza, and A. M. Echavarren, Functionalized Truxenes: Adsorption and Diffusion of Single Molecules on the KBr(001) Surface ACS Nano, 4, (6), (2010), 3429 [4] R. Pawlak, S. Kawai, S. Fremy, T. Glatzel and E. Meyer, Atomic-scale mechanical properties of orientated C60 molecules revealed by noncontact atomic force microscopy, ACS Nano, 5, (8), (2011), 6349-54 [5] R. Pawlak, S. Fremy, S. Kawai, T. Glatzel, H. Fang, L.-A. Fendt, F. Diederich, and E. Meyer, Directed rotations of single porphyrin molecules controlled by localized force spectroscopy, ACS Nano, 6, (2012), 6318–6324

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Advance characterization of nanostructures using nc-AFM/STM measurements

P. Jelinek Institute of Physics of the ASCR, Curkrovarnicka 10, 162 00 Prague, Czech Republic

Increasing number of precise simultaneous force/tunneling current measurements has been reported last years (see e.g. [1]). The possibility of combining the powerful tools provided by scanning tunneling (STM) and atomic force microscopy (AFM) in a single instrument brings the unique opportunity to correlate tip-surface short-range chemical forces with simultaneously measured tunneling currents at the atomic scale. Among others, this opens new possibilities to characterize not only charge transfer through an established chemical bond between atoms [2] but simultaneously its strength as function of bias and tipsample distance. In particular, it opens a new way to establish direct relation between fundamental physical entities, such as the tunneling current and the chemical force [3]. In this talk, we will discuss basic principles and obstacles of the simultaneous detection of the atomic forces and the tunneling current from theoretical and experimental point of view. We will discus (i) chemical composition of complex 1D nanostructures [4]; (ii) discrimination of simple molecules on semiconductor surfaces [5]; (iii) relation between the tunneling current and the chemical force [2,3] and (iv) AFM/STM measurements on a single molecule deposited on semiconductor surface.

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References: [1] F.J. Giessibl, Appl. Phys. Lett. 76, 1470 (2000) [2] M. Ternes et al , Phys. Rev. Lett. 106, 016802 (2011) [3] P. Jelinek et al J. Phys.-Cond. Mat. 24, 084001 (2012) [4] M. Setvin, et al, ACS Nano 6, 6969 (2012) [5] Z. Majzik et al, (ACS Nano DOI: 10.1021/nn400102m)

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Intricate Mechanism of Lateral and Vertical Manipulation of Super-Cu Atoms on the Cu:O Surface: Experiment and Theory

J. Bamidele,1 Y. Kinoshita,2 R. Turansky,3 S. H. Lee,2 Y. Naitoh,2 Y. J. Li,2 Y. Sugawara,2 I. Stich,3 and L. Kantorovich1 1

Department of Physics, King’s College London, London, United Kingdom 2 Department of Applied Physics, Osaka University, Osaka, Japan 3 Center for Computational Material Science, Inst. of Physics, Bratislava, Slovakia

We present a join experimental and theoretical study of lateral and vertical manipulations of “super”-Cu atoms on the oxygen-terminated p(2x1) Cu(110) surface with Non-Contact Atomic Force Microscopy (NC-AFM). The surface consists of rows of alternating Cu and O atoms on the bare Cu(110) surface. Cu adatoms occupy positions between two adjacent Cu-O rows opposite two O atoms in each of them. Using NC-AFM we find that using an O terminated tip [1] vertical manipulation events, consisting of both removal and deposition of Cu atoms, are frequently seen, Fig. 1 (right). Interestingly, no change of contrast is observed. At the same time, lateral manipulation events were observed only at the edges of c(6x2) islands, no lateral manipulation was found to be possible on the p(2x1) terraces. In order to understand these observations, we attempted a comprehensive theoretical study of both lateral and vertical manipulations of the super-Cu atoms on the p(2x1) Cu(110):O surface with the O-terminated NC-AFM tip. Using Density Functional Theory (DFT) calculations in conjunction with Nudged Elastic Band (NEB) method for calculating transition barriers, as well as Kinetic Monte Carlo (KMC) simulations, we propose detailed mechanisms of both lateral and vertical manipulations, which fully explain experimental observations. We find that both mechanisms depend crucially on the initial tip-surface separation. At not very small separations a super-Cu atom under the tip (state S) can be thermally

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activated into an intermediate (I) position between the tip and surface, Fig. 1 (left). Upon tip retraction, the atom remains in this state until the barrier to jump to the tip (state T) is sufficiently reduced. Upon reaching state T, however, the Cu atom immediately moves higher up on the tip (state U), so that tip apex remains O-terminated with only secondary features in the imaging contrast affected. The deposition of the Cu atom from the tip to the surface happens when the barrier for the atom from U to T state is reduced which happens at smaller separations. Therefore, the mechanism consists of several stages: three stochastic (thermal with en energy barrier) and one conservative (dragging), which happen in between. KMC simulations confirm the viability of this mechanism and give statistics information. We find that lateral manipulation (based on a certain deviation of the above mechanism) can only be rationalized if the tip comes much closer to the surface, which explains why these particular events were not frequently observed References: [1] J. Bamidele et al. – Phys. Rev. B 86 (2012) 155422

Figures:

Figure 1: Intermediate state of the Cu atom (left) and the NC-AFM image during manipulation (right) with super-Cu atoms clearly visible on the terrace (central area) alongside some vertical manipulation events. The edge of the c(6x2) island is seen in the right part of the image

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Photoactivated Covalent Bonding of Organic Molecules on an Insulator Surface

Robert Lindner1, Markus Kittelmann1, Philipp Rahe2, Christopher M. Hauke1, Markus Nimmrich1 and Angelika K체hnle1 1

Institut f체r Physikalische Chemie, Johannes Gutenberg-Universit채t Mainz, Germany 2 Department of Physics and Astronomy, The University of Utah, Salt Lake City, USA

Controlled surface functionalization is crucial for future technologies like molecular electronics. In order to increase the stability and functionality of selfassembled structures, covalent linking of organic molecules is a most promising approach. Thermally induced covalent bonding on metallic and insulating substrates has been demonstrated in impressive ways [1, 2]. The downside of this approach is that the same external stimulus is used for the deposition as well as for the covalent linking of the molecules. In order to gain further control, photochemical linking provides an elegant method to separate the two functionalization steps. Photopolymerization of bulk C60 Fullerene has been described in literature and the reaction mechanism has been assigned to a [2+2]-cycloaddition [4]. In this work, we study the photopolymerization of C60 on CaCO3(10.4). C60 is known to form well-ordered monolayer islands on calcite [3]. We examined these C60 islands with non-contact atomic force microscopy before and after irradiation with a laser (Fig.1). Interestingly, the molecular structure is changed significantly upon irradiation, which is ascribed to the formation of a two-dimensional, polymeric network. The successful photoreaction was confirmed by a change in the C60 superstructure and a change in intermolecular distances (see Fig.1).

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References: [1] Grill, L. Dyer, M. Lafferentz, L. Persson, M. Peters, M. V.; Hecht, S. Nature nanotechnology 2007, 2, 687-691 [2] Kittelmann, M. Rahe, P. Nimmrich, M. Hauke, C. M. Gourdon, A.; Kühnle, A. ACS nano 2011, 5, 8420–8425 [3] Rahe, P., Lindner, R., Kittelmann, M., Nimmrich, M., Kühnle, A., Physical chemistry chemical physics 2012, 14, 6544–6548. [4] Zhou, P., Dong, Z., Rao, A. M., Eklund, P. C., Chemical Physics Letters 1993, 211, 337– 340

Figures:

Figure 1: Monolayer islands of C60 on the calcite (10.4) surface; a) Before irradiation a hexagonal arrangement and a moiré pattern can be seen; b) After irradiation, the moiré pattern has vanished and polymerized domains become visible, as indicated by the white arrows

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Imaging Atoms and Bonds by Atomic Force Microscopy

Nikolaj Moll, Leo Gross, Bruno Schuler, Fabian Mohn, Alessandro Curioni, and Gerhard Meyer IBM Research – Zurich, Säumerstrasse 4, CH-8803 Ruschlikon, Switzerland

Using functionalized tips, the atomic resolution of a single organic molecule can be achieved by noncontact atomic force microscopy (nc-AFM) operating in the regime of short-ranged repulsive Pauli forces. The van-der-Waals and electrostatic interactions only add a diffuse attractive background and do not contribute to atomic contrast. To theoretically describe the atomic contrast in such AFM images, a simple model is proposed in which the Pauli repulsion is assumed to follow a power law as a function of the probed charge density. For a single molecules imaged with a CO-terminated tip, we find excellent agreement with the experimental data. Experimentally, different bond orders of individual carboncarbon bonds in organic molecules can be distinguished by AFM with a COterminated tip. Two different contrast mechanisms exist, which were corroborated by calculations: The greater electron density in bonds of higher bond order led to a stronger Pauli repulsion, which enhanced the brightness of these bonds in high-resolution AFM images. The apparent bond length in the AFM images decreased with increasing bond order because of tilting of the CO molecule at the tip apex. References: [1] Leo Gross, Fabian Mohn, Nikolaj Moll, Peter Liljeroth, and Gerhard Meyer, Science 325,1110-1114 (2009) [2] Nikolaj Moll, Leo Gross, Fabian Mohn, Alessandro Curioni, and Gerhard Meyer, New Journal of Physics 14, 083023 (2012) [3] Leo Gross, Fabian Mohn, Nikolaj Moll, Bruno Schuler, Alejandro Criado, Enrique Guitián, Diego Peña, André Gourdon, and Gerhard Meyer, Science 337, 1326–1329 (2012)

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Water and metal adsorbates on reducible oxide surfaces: Can theory help to understand the AFM and KPFM contrast?

D. Fernández-Torre1, M. Todorovic1, P. Pou1 and R. Pérez1,2 1

Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain 2 Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain ruben.perez@uam.es

Metal oxides play a key role in a wide range of technological applications. To optimize their performance, it is essential to understand their surface properties and chemistry in detail. Noncontact atomic force microscopy (nc-AFM) provides a natural tool for atomic-scale imaging of these insulating materials. Some of these materials, including ceria (CeO2), and particularly titania (TiO2), have been extensively studied with nc-AFM in the last few years. Experiments on the rutile TiO2(110) surface show, at variance with STM, that a variety of different contrasts can be obtained, and frequent changes among different imaging modes are observed during scanning. The two most common contrasts are the “protrusion” and the “hole” mode imaging modes, that correspond, to imaging bright the positive or the negative surface ions respectively, but other contrasts like the “neutral” mode and the “all-inclusive” mode –where all the different chemical species and defects are imaged simultaneously—have been also identified. Understanding the image contrast mechanisms and characterizing the associated tip structures is crucial to extract quantitative information from nc-AFM measurements and to identify the nature of the observed defects. While in many cases the same nc-AFM image can be explained by different models, and even different underlying tip-sample interactions, we show here that the combination of force spectroscopy (FS) measurements and first-principles simulations can provide an unambiguous identification of the tip structure and the image contrast mechanism [1]. In particular, we show that the best tips to explain the protrusion

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and hole mode forces are TiOx-based clusters differing in just one H atom at the tip apex, discarding previously proposed Ti-terminated tips that would lead to forces much larger than the ones observed in the experiments. The less frequent neutral and all-inclusive images are associated to Si tips where contamination is limited to just an O atom or OH group at the apex. These models provide a natural explanation to the observed contrast reversals by means of H transfer to/from the tip, an event that we indeed observe in our simulations. As tip contamination by surface material is common while imaging oxides, we expect these tips and imaging mechanisms to be valid for other oxides. Our results for the imaging of water on CeO2 [2], defects on the CuO surface oxide [3] and of metal adsorbates on TiO2 support this conclusion. We acknowledge the contribution of our experimental collaborators A. Yurtsever, Y. Sugimoto, M. Abe and S. Morita, Graduate School of Engineering, Osaka University (Japan) and M. Z. Baykara, H. Monig, E. Altman and U. D. Schwarz, Yale University (USA). References: [1] A. Yurtsever et al., Phys. Rev. B 85, 125416 (2012) [2] D. Fernรกndez-Torre et al., J. Phys. Chem. C 116, 13584 (2012) [3] M. Z. Baykara et al., submitted (2013)

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Benzoic acids on calcite: From templated assembly to on-surface synthesis

Philipp Rahe1,2, Markus Kittelmann2, Markus Nimmrich2, André Gourdon3 and Angelika Kühnle2 1

Department of Physics and Astronomy, The University of Utah, Salt Lake City, USA 2 Institut für Physikalische Chemie, Johannes Gutenberg Universität Mainz, Germany 3 CNRS, CEMES, Nanoscience Group, Toulouse, France

Fundamental surface-supported processes such as chemical transformations and reactivity of organic molecules are of utmost importance for a large number of daily-life applications [1]. Benefiting from a detailed understanding of moleculemetal interactions, pivotal experiments have very recently demonstrated the potential of the on-surface synthesis concept. By the thermal activation of precursor molecules, stable molecular structures with tailored properties have been achieved, however, these studies have been limited to metallic substrates [2-4]. Nevertheless, for many applications such as molecular (opto-) electronic devices, it would be exceedingly attractive to transfer the assembly and reaction principles to bulk insulator substrates where an electronic coupling and leakage to the underlying conductor is avoided. The calcite (1014) surface has very recently been introduced as one of the most promising substrates for molecular adsorption at room temperature [5]. First, by using non-contact atomic force microscopy we will here present the structure formation of small benzoic acid molecules on this surface. Most notably, the resulting structures are templated by the underlying calcite substrate [6]. In a second step, we demonstrate the covalent linking of different halide substituted benzoic acids on calcite. The presence of the carboxylate group is expected to weaken the phenylhalide bond and, therefore, favour homolytic

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cleavage of this bond leading to reactive phenyl radicals after heating to moderate temperatures. By varying the number and position of the halide substitutions, we rationally design the resulting structures revealing dimers, straight lines as well as zig-zag structures and, thus, provide clear evidence for the covalent linking step [7]. References: [1] N. Nilius et al. Top. Catal. 54 (2011) 4 [2] L. Grill et al., Nature Nanotech. 2 (2007) 687 [3] A. Gourdon, Angewandte Chemie 47 (2008) 6950 [4] G. Franc et al., Phys. Chem. Chem. Phys. 13 (2011) 14283 [5] P. Rahe et al., small 19 (2012) 2969 [6] P. Rahe et al., Phys. Chem. Chem. Phys. 14 (2012) 6544 [7] M. Kittelmann et al., ACS Nano 5 (2011) 8420

Figures:

Figure 1: High-resolution NC-AFM images of various benzoic acid molecules presenting surface templating (a, b) and covalent linking (c-e).

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Dynamic Force Imaging and Spectroscopy of Individual Molecules on Thin Insulating Films

Jascha Repp Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany

Ultrathin insulating films on metal substrates facilitate the use of the scanning tunneling microscope (STM) to study the electronic properties of single atoms and molecules, which are electronically decoupled from the metallic substrate. We investigated dibenzo[a,h]thianthrene adsorbed on ultrathin layers of NaCl by means of atomic force-microscopy (AFM) in a combined STM/AFM based on the qPlus-sensor [1]. We used CO-functionalized tips as has been introduced recently by Gross and co-workers [2]. The non-planar molecules exist in two stable conformations. By means of excitations from inelastic tunneling electrons we can switch between both conformations. We present atomic force microscopy (AFM) measurements with with submolecular resolution directly revealing the conformational changes [3]. From AFM data and taking the chirality of the molecules into account, we could unambiguously determine the pathway of the conformational change. Hence, the AFM channel reveals additional information that is truly complementary to the STM data set. For an even larger non-planar thiathrene derivative C20S2H12 we also identified the structure from AFM data. In recent studies in particular CO-functionalized tips enabled imaging with unprecedented resolution. Unfortunately, the molecular geometry appears distorted, an effect that is attributed to the bending of the CO-molecule at the tip apex in the force field of the sample. Whereas in many cases a slight distortion of the images may not affect the experimental findings, in some cases, the detailed

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geometric structure itself bares crucial information. We present a technique to correct for the image distortions that are due to this effect. References: [1] F. J. Giessibl, Appl. Phys. Lett. 76, 1470 (2000) [2] L. Gross, F. Mohn, N. Moll, P. Liljeroth, and G. Meyer, Science 325, 1110 (2009) [3] N. PavliÄ?ek, B. Fleury, M. Neu, J. NiedenfĂźhr, C. Herranz-Lancho, M. Ruben, and J. Repp, Phys. Rev. Lett. 108, 086101 (2012)

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Isolated dangling bonds on H:Ge(001) surface

B. Such, M. Kolmer, Sz. Godlewski, M. Wojtaszek, R. Zuzak, J. Budzioch, M. Szymoński Centre NANOSAM, Inst. of Physics, Jagiellonian Univ., ul. Reymonta 4, PL-30-059 Krakow, Poland Bartosz.Such@uj.edu.pl

Both geometric and electronic structures of the Ge(001) surface change upon hydrogen adsorption since almost all the dangling bonds present on the surface are passivated. However, certain number of isolated single and double dangling bonds remain intact. Moreover, it is possible to form new defects in a controlled way by tip-induced desorption of hydrogen. In the presentation, we will present the results of STM and NC-AFM investigation into properties of such defects. A force 3D spectroscopy of a single dangling bond defect shows characteristic spatial distribution of the interaction. While the force curves over hydrogen atoms surrounding the defect show no sign of attractive interaction, the force curves over the defect has a range where the short-distance attractive force is detected. On the other hand, a double dangling bond forms a switch, since naturally it stays in a tilted configuration. The controlled switching is possible both by STM and NCAFM. Additionally, it is possible to alternate the local electronic structure by creation of patterns of defects giving a chance to form a wire-like structures for molecular electronics.

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Mechanical atom manipulation using atomic force microscopy at room temperature

Yoshiaki Sugimoto Graduate School of Engineering, Osaka University 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan sugimoto@afm.eei.eng.osaka-u.ac.jp

The manipulation of individual atoms and molecules at surfaces is of great importance for future nanoscale devices, as well as for the investigation of fundamental physical and chemical phenomena occurring at the atomic scale. The ability to construct multifunctional nanostructures with desired properties on the atomic scale has important consequences for a number of important applications, including catalysis, quantum computing devices, and functional nanomaterials. The formation of such specially designed nanostructures has been demonstrated utilizing the atomic manipulation capability of scanning tunneling microscopy (STM) at cryogenic temperatures [1, 2]. It has been shown that fine control of the tip target atom interaction force is required for delicate positioning of individual atoms to a specified location in STM manipulation [3]. The interaction force in a STM experiment can be estimated indirectly by the tunneling conductance. On the other hand, the invention of atomic force microscopy (AFM) has extended the unique capability for atom manipulation on surfaces that are inaccessible to STM [4], and more importantly, provides an opportunity to directly measure the forces [5] involved in the atom manipulation process [6-8]. Here, we present an investigation of the effect of the tip on lateral manipulation using AFM at room temperature. The atom hopping probabilities associated with different manipulation processes as a function of the tip-surface distance are investigated by means of constant height scans with various tips, the interaction of which with surface atoms are evaluated by force spectroscopic measurements.

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We demonstrate that the efficiency for manipulation is extremely dependent on the nature of the tip-apex chemical properties References: [1] D.M. Eigler and E.K. Schweizer, Nature 344 (1990) 524 [2] A.J. Heinrich, C.P. Lutz, J.A. Gupta, and D.M. Eigler, Sicence 298 (2002) 1381 [3] S.-W. Hla, K.-F. Braun, and K.-H. Rieder, Phys. Rev. B, 67 (2003) 201402 [4] I. Yi, R. Nishi, M. Abe, Y. Sugimoto, and S. Morita, Jpn. J. Appl. Phys. 50 (2011) 015201 [5] M. Lantz, et al., Science 291 (2001) 2580 [6] M. Ternes, et al., Science 319 (2008) 1066 [7] Y. Sugimoto, et al., Phys. Rev. Lett. 98 (2007) 106104 [8] M Y. Sugimoto, et al., Science 322 (2008) 413

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Understanding molecular interactions using NCAFM: can we move 'beyond' imaging?

Adam Sweetman, Samuel Jarvis, Andrew Stannard, Andrew Lakin, Cristina Chiutu, Lev Kantorovich, Janette Dunn, and Philip Moriarty School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, U.K. adam.sweetman@nottingham.ac.uk

Both NC-AFM and STM have been used to great success in understanding the role of molecule-molecule interactions on surfaces, and recently impressive results have been obtained showing sub-molecular resolution during the imaging of single molecules by the controlled functionlisation of a scanning probe tip with inert molecular and atomic species [1-3]. Measurement of inter-molecular interactions has also been shown by using 'inverse' imaging, that is, functionalising the tip with the molecule of interest and 'inverse' imaging the adsorbed molecule with both well characterised surface features and other adsorbed molecules [4-5]. Using these techniques allows for the exciting possibility of directly probing intermolecular interactions in three dimensions with sub-molecular resolution. Such experiments might offer a fascinating insight into molecular interactions, but a key issue in interpreting data produced in such 'tipfunctionalised' experiments remains that the orientation of the tip adsorbed molecule is (in general) unknown. In this talk I will offer an overview of moleculeon-molecule interactions measured using NC-AFM at cryogenic temperatures, and suggest possible routes by which the tip molecule orientation might be determined. References: [1] Gross, Leo, et al. "The chemical structure of a molecule resolved by atomic force microscopy." Science 325.5944 (2009): 1110-1114

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[2] Gross, Leo, et al. "Bond-Order Discrimination by Atomic Force Microscopy."Science 337.6100 (2012): 1326-1329 [3] Kichin, G., et al. "Calibrating atomic-scale force sensors installed at the tip apex of a scanning tunneling microscope." Physical Review B 87.8 (2013): 081408 [4] Schull, Guillaume, et al. "Atomic-scale engineering of electrodes for single-molecule contacts." Nature Nanotechnology 6.1 (2010): 23-27 [5] Chiutu, C., et al. "Precise Orientation of a Single C_ {60} Molecule on the Tip of a Scanning Probe Microscope." Physical Review Letters 108.26 (2012): 268302

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Molecules in the transport path: The mechanical properties of STM junctions “in contact”

F.S. Tautz Peter Grünberg Institut, Forschungszentrum Jülich, 52425 Jülich, Germany s.tautz@fz-juelich.de

In recent years, scanning tunneling microscopes (STM) have been used increasingly as devices to establish atomically defined contacts to surfaces. For the STM this has created new opportunities in various fields, ranging from quantum transport studies through nanostructures [1] to ultra-high resolution microscopy [2]. The next challenge is the combination of electrical measurements in these contacts with experiments that reveal the mechanical properties and the structure of the junction “in contact” directly. This can be achieved by equipping the tunneling microscope with a tuning fork sensor that measures the gradient of the acting force via the frequency shift of the tuning fork oscillation. In this talk I will illustrate the benefits of combining force with current detection when molecules are in the transport path between the STM tip and the surface. Two experiments will be considered: (1) a molecular wire is lifted up between tip and surface as the tip retracts from the surface, (2) a sensor molecule is present in the tunneling junction, yielding very high lateral image resolution as the tip is scanned across the surface in near contact (scanning tunneling hydrogen microscopy, STHM). (1) Measuring the conductance of molecular wires in well-defined geometries is still a challenge. We have shown some time ago that molecules can be contacted with an STM tip at defined positions and lifted up by tip retraction [3]. In this experiment the upper contact at the tip is defined, but for any given tip height the

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precise structure of the remainder of the molecule in the junction is still not known from experiment. For example, it is not clear from the conductance vs. tip height spectrum when exactly the molecule reaches the freestanding wire configuration. However, when simultaneous force detection is added, it becomes possible to determine the structure of the molecule in the junction from its mechanical response unambiguously, and in this way the intrinsic conductance of a free standing molecular wire under full structural control can be measured for the first time [4]. We have applied this to a class of conjugated molecular wires of varying lengths. Incidentally, the force gradient signal can also be used to measure the adsorption energy of a single molecule on the surface and to partition this energy between various bonding channels [5]. (2) It has been shown that atomic and molecular sensor particles in the tunneling junction lead to a dramatic enhancement of the lateral STM resolution, revealing the geometric structure of surfaces (STHM) [2]. We have suggested that this remarkable image resolution is due to force detection in the conductance channel [6]. I will show that the simultaneous detection of the force gradient signal in the tuning fork AFM and the tunneling conductance in STHM mode allows a force calibration of this conductance signal and gives further insights into the mechanism of image generation in STHM [7]. References: [1] C. Toher et al., PRB 83, 155402 (2011); A. Greuling et al., PRB 84, 125413 (2011); T. Brumme et al., PRB 84, 115449 (2011) [2 R. Temirov et al., New J Phys 10, 053012 (2008); C. Weiss et al., JACS 132, 11864 (2010); G. Kichin et al., JACS 133 16847 (2011) [3] R. Temirov et al., Nanotechnology 19, 065401 (2008) [4] N. Fournier et al., PRB 84, 035435 (2011) [5] C. Wagner et al., PRL 109, 076102 (2012) [6] C. Weiss et al., PRL 105, 086103 (2010) [7] G. Kichin et al. PRB 87, 081408(R) (2013)

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Investigation of the mechanical properties of a monoatomic layer by combined STM and AFM measurements

Markus Ternes Max Planck Institut, Germany

The advent of nanoscale engineered materials has started to revolutionize material science and technology. Further improvement is expected when tailoring the materials down to the atomic scale. For this and for developing functional systems a detailed understanding not only of the electronic but also of the mechanical properties at nanometer scale is of crucial importance. Here we study an insulating single atomic layer of hexagonal boron-nitride (h-BN) on Rh(111). The lattice mismatch between the substrate and the h-BN produces a strongly corrugated hexagonal superstructure with 3.2 nm periodicity [1,2]. This superstructure has been shown to be an excellent nanotemplate [3] which allows to decouple electronically molecules and clusters from the underlying substrate [4,5]. To measure its mechanical properties we use a home-built combined scanning tunneling and atomic force microscope operating at low temperatures and with sub-nm oscillation amplitudes. From 3-dimensional frequency shift data we calculate the total energy landscape and lateral and vertical forces acting between the probing tip and the h-BN layer. Slight variations in the forces between the different alignments of the rim sites of the hexagonal corrugation in respect to the Rh surface enable us to derive the elastic properties of the corrugated layer. Our

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findings are further supported by a statistical evaluation of the lateral displacement of the BN hexagons in atom resolved measurements References: [1] M. Corso et al., Science 202, 217 (2004) [2] R. Laskowski et al., Phys. Rev. Lett. 98, 106802 (2007) [3] H. Dil et al., Science 319, 1824 (2008) [4] S. Bose et al., Natuer Mat. 9, 550 (2010) [5] S. Kahle et al., Nano Lett. 12, 518 (2012)

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Developing realistic models of interfaces from simulation

Matt Watkins London Centre for Nanotechnology, UK

I will describe several recent pieces of work focusing on developing an atomisticlevel understanding of interfaces. A variety of computational approaches are used, and compared to state-of-the-art experiments using the non-contact atomic force microscope (NC-AFM). (i) Insulator – molecule – metal. In collaboration with NC-AFM experimental researchers at the University of Hamburg, we unambiguously identified the adsorption configurations of a complex molecule on ionic crystals (NaCl, NiO) and the nature of surface ions [1,2,3]. These systems can provide a sensitive test system to calibrate the accuracy of computational approaches and also act as a tape measure, providing an accurate measure of tip-sample distance, which is extremely hard to estimate independently. The identification of a permanent tip dipole inherent to metallic tips opens the way to using this mode of AFM operation for metrology of complex insulating surfaces. (ii) Insulator – water. High-resolution imaging and force spectroscopy using AFM in solution opens a wide area of possible applications allowing real-time and realspace imaging of surfaces in solution. To obtain full benefit and provide a significant new analytical ability, it is vital to understand the underlying imaging mechanism(s) that can lead to high (atomic or molecular) resolution. Our simulations of solvated nanoparticles near surfaces show several possible mechanisms that lead to measurable force differences and image contrast over

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surface sites [4]. We used a variety of simulation methods to calculate the free energies of nanoparticle-surface interactions [5]. Water-mediated interactions can cause significant force differences above different surface sites, and are in most cases larger, and longer ranged, than the direct vacuum-like interactions. I will compare and contrast predicted imaging mechanisms from vacuum with solution. References: [1] A. Schwarz, D. Z. Gao, K. L채mmle, J. Grenz, M. B. Watkins, A. L. Shluger, and R. Wiesendanger, J. Phys. Chem. C 117 1105 (2013) [2] G. Teobaldi, K. Lammle, T. Trevethan, M. Watkins, A. Schwarz, R. Wiesendanger and A. L. Shluger, Phys. Rev. Lett., 106, 216102 (2011) [3] , T. Trevethan, A. Schwarz, M. Watkins, A. L. Shluger and R. Wiesendanger, Nano Letters, 10 2965 (2010) [4] M. Watkins, A. L. Shluger, Phys. Rev. Lett., 105 196101 (2010) [5] B. Reischl, M Watkins, and A. S. Foster, J. Chem. Theory Comput., 9, 600 (2013)

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Cover image: High resolution NC-AFM images of the deprotonation step of 2,5-dihydroxybenzoic acid and the thermally covalently linked 4-iodo benzoic acid, 2,5-diiodo benzoic acid, 2,5dichloro benzoic acid and 3,5-diiodo salicylic acid on the calcite (10.4) surface. Credit: Angelika Kühnle Institut für Physikalische Chemie Johannes Gutenberg Universität Mainz, Germany

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Imaging and Manipulation of Adsorbates using Dynamic Force Microscopy