Graphene 2012 Abstract Book April 10-13, 2012 Brussels (Belgium) by Phantoms Foundation

On behalf of the International, Scientific and Technical Committees we take great pleasure in welcoming you to Brussels for the second edition of the International Conference Graphene. A plenary session with internationally renowned speakers, extensive thematic workshops in parallel, oneto-one meetings (Brokerage Event) and a significant industrial exhibition featuring current and future Graphene developments will be highlighted at the event. Graphene 2012 is now an established event, attracting global participants intent on sharing, exchanging and exploring new avenues of graphene-related scientific and commercial developments. We truly hope that Graphene 2012 serves as an international platform for communication between science and business. The organizers are also pleased to welcome Grafoid Inc., a Canadian graphene development and patenting joint venture, as lead sponsor of this year’s event. They join many other remarkable institutions in supporting the second edition of Graphene conference. Grafoid Inc. is a privately-held graphene investment and technology company intent on establishing a mass production process for economically scalable graphene. We are also indebted to the following Scientific Institutions, Companies and Government Agencies for their help and/or financial support: Phantoms Foundation, Université Catholique de Louvain, ONERA, Centre National de la Recherche Scientifique, CIN2 (ICN-CSIC), Grafoid Inc., Graphene Flagship Pilot Action, Consiglio Nazionale delle Ricerche, Oxford Instruments, Aixtron, Thermo Fisher Scientific, Instituto Español de Comercio Exterior (ICEX), Fonds de la Recherche Scientifique (FNRS), GDRI: Graphene-Nanotubes, SSCP and MULT-EU-SIM project. We also would like to thank all the exhibitors and participants that join us this year. One thing we have for granted: very few industries, one way or another, will escape from the influence of Graphene and the impact on businesses is here to stay. Hope to see you again in the next edition of Graphene 2013 to be held during ImagineNano event (www.imaginenano.com) in Spain.

Graphene 2012 Organising Committee

Committees

Organising Committee

Jean-Christophe Charlier Antonio Correia

Annick Loiseau Stephan Roche

Université Catholique de Louvain (Belgium) Phantoms Foundation (Spain) ONERA-CNRS and GDRI, Int. Research Group on Graphene and Nanotubes (France) CIN2 (ICN-CSIC) (Spain)

Local Organising Committee

Jean-Christophe Charlier Luc Henrard

Université Catholique de Louvain (Belgium) Facultés Universitaires Notre-Dame de la Paix de Namur (Belgium)

COMMITTEES

International Scientific Committee

Adrian Bachtold Alexander Balandin Antonio Castro Neto Hui-Ming Cheng Gianaurelio Cuniberti Toshiaki Enoki Andrea Ferrari Mar Garcia-Hernandez Mark Goerbig Pablo Jarillo-Herrero Jari Kinaret Alessandra Lanzara Pierre Mallet Charles Marcus Vincenzo Palermo François Peeters Alain Pénicaud Loh Kian Ping Young Woo Son

Catalan Institute of Nanotechnology (Spain) University of California (USA) National University of Singapore (Singapore) Institute of Metal Research (China) Technische Universität Dresden (Germany) TITECH (Japan) University of Cambridge (UK) ICMM-CSIC (Spain) LPS Orsay (France) MIT (USA) University of Chalmers (Sweden) Lawrence Berkeley National Laboratory (USA) Institut Néel - CNRS (France) Harvard University (USA) CNR-ISOF (Italy) University of Antwerpen (Belgium) University of Bordeaux (France) National University of Singapore (Singapore) Korea Institute for Advanced Study (Korea)

Lead Sponsor

Platinum Sponsors

Gold Sponsors

SPONSORS

Silver Sponsors

Lead Sponsor

GRAFOID Grafoid is a Canadian technology joint venture company. We invest and we manage high-growth, scalable graphene investments, patents and material applications. Our aim is to create the global standard for an economically scalable graphene and engage in strategic opportunities with industrial partners. Grafoid’s pristine quality graphene comes from the world’s best graphite source, Focus Metals’ Lac Knife, Quebec deposit. The inherent, conductive values of the graphite source remain undiminished through Grafoid’s top-down extraction and transformation process that respects nature to the highest level.

Platinum Sponsors

OXFORD INSTRUMENTS Oxford Instruments is a leading supplier of high technology tools and systems for research and industry, specialising in equipment that can fabricate, manipulate, characterise and analyse matter at the smallest scale. We are opening up the exciting world of graphene with our innovative toolbox of techniques and products, helping our partners to reveal even more of the nano-world. To find out more about how a partnership with Oxford Instruments can unlock challenging possibilities, please visit our booth or www.oxford-instruments.com

SPONSORS

GRAPHENE FLAGSHIP This pilot action GRAPHENE-CA paves the road to the FET Flagship "Graphene-Driven Revolutions in ICT and Beyond" (GRAPHENE). The GRAPHENE flagship ambition is to bring together a focused, interdisciplinary European research community that aims at a radical technology shift in information and communication technology that exploits the unique properties of graphene and related two-dimensional materials. Graphene research is an example of an emerging translational nanotechnology where discoveries in academic laboratories are rapidly transferred to applications and commercial products.

NATIONAL RESEARCH COUNCIL OF ITALY (CNR) The National Research Council (CNR) is the largest Italian institution dedicated to scientific research; its duty is to carry out and spread research activities in the main sectors of knowledge, and applications of research to the economic and social development of the country. To this end, the activities of the organization are divided into macro areas of interdisciplinary research: biotechnology, medicine, materials, environment and land, information and communications, advanced systems of production, judicial and socio-economic sciences, classical studies and arts. CNR is distributed all over Italy through a network of institutes aiming at promoting a wide diffusion of its competences throughout the national territory, and has a long-lasting experience in both supervising large research projects at national level as well as participating to larger european network of joint research within the past and presents EU framework programs.

Gold Sponsors AIXTRON AIXTRON has enabled researchers all over the world to grow high quality graphene using our equipment, from small chips to 4-inch or 6-inch diameter substrates, and even on industrial 12-inch wafer-scale. We are a leading provider of state of the art equipment to the semiconductor industry with over 28 years of experience in producing research and production equipment. Our technologies cover the deposition of carbon, silicon, III-V and II-VI materials for electronics, display, storage, lighting and energy applications using technologies such as CVD, PECVD, MOCVD and ALD. THERMO FISHER SCIENTIFIC Thermo Fisher Scientific, the world leader in serving science enables its customers to make the world healthier, cleaner and safer by providing analytical instruments, equipment, reagents and consumables, software and services for research, analysis, discovery and diagnostics. The company delivers a broad selection of analytical instruments, equipment, consumables and laboratory supplies. Its products includes innovative technologies for mass spectrometry, elemental analysis, molecular spectroscopy, sample preparation, informatics, fine and high-purity chemistry production, cell culture, RNA interference analysis and immunodiagnostic testing, as well as air and water quality monitoring and process control.

Founded in 1425, one of Europeâ&#x20AC;&#x2122;s oldest universities, UCL has over 27,000 students on five sites (Louvain-la-Neuve, Bruxelles, Mons, Tournai). UCL educates almost one in every two French-speaking Belgians, and attracts every year 4,000 international students from around the globe (a number of programmes are given in English). UCL trains students in all disciplines, from beginnerâ&#x20AC;&#x2122;s level through doctorate level and on to adult continuing education. Teaching is based on solid research and innovation. UCL is also one of the 22 European Universities to have received the ECTS label, a UE recognition of the quality of its management of international exchanges.

SPONSORS

UNIVERSITE CATHOLIQUE DE LOUVAIN

ICEX The Spanish Institute for Foreign Trade (ICEX, “Institutito Español de Comercio Exterior”) is the Spanish Government Agency serving Spanish companies to promote their exports and facilitate their international expansion, assisted by the network of Spanish Embassy’s Economic and Commercial Offices and, within Spain, by the regional and Territorial Offices. It is part of the Spanish Ministry of Economy and Competitiveness (“Ministerio de Economía y Competitividad”)

ESPAÑA TECHNOLOGY FOR LIFE This program, carried out by ICEX, focuses in the promotion in foreign markets of Spain’s more innovative and leading industrial technologies and products.

Silver Sponsors FNRS Fund for Scientific Research-FNRS is a key player in fundamental research in the French Community of Belgium. F.R.S.-FNRS has supported and championed free scientific research in all scientific fields for over 80 years. Building on expertise and partnerships, the F.R.S.-FNRS fosters innovation and knowledge development by selecting, supporting and evaluating researchers and research projects within university laboratories. A respected institution within Belgium, the F.R.S.- FNRS is a driving force behind the competitiveness of Belgian research in Europe and worldwide. The mission of F.R.S.FNRS is to contribute to the development of a competitive knowledge society by supporting researchers and their initiatives and disseminating scientific research.

SPONSORS

GRAPHENE AND NANOTUBES – GDRI The "Graphene and Nanotubes: science and applications" ("GNT") group is a national research group (GDR 3217) and an international coordination network (GDRI) cross-linking research on nanotubes and graphene. Its scientific activity is based on three vital and emerging research themes, which develop knowledge of basic properties of individual nano-objects as well as their manipulation for developing devices linked to the industrial and socio-economical world. The group gathers French, European and Canadian partners who have played a major role in the activities of the previous GDR, and to which are added scientists of international reputation working on graphene.

SSCP SSCP was established in 1973 and grew up as a specialty coating company. In 1997, SSCP stepped into electronic material & component industry and made a distinguished performance in Optical Fiber, Printed Electronics, and EMI Filters. With its accumulated technologies and facilities, SSCP recently succeeded to commercialize Graphene, the material with astonishing thermal and electronic properties. SSCP is now fully geared to mass product Graphene powders, pastes, inks and films, which will be applied to LED TV, Mobile Devices, OLED, Secondary Batteries and Transparent Electrodes. Industry struggled with thermal problems will welcome those products. MULT.EU.SIM MULT.EU.SIM aims to gather the simulation research community in Europe to establish a joint vision of multiscale modelling and simulation. This will enable to prepare Europe to play a leading role in the opening era of computational sciences where multiscale simulation will profoundly change the scientific and technological practices. This European vision will serve as the foundation for a joint effort with emphasis toward multiscale unified codes and standardized interfaces & workflows in a field that is currently very fragmented. Ultimately, the availability of such a multiscale code toolbox will put Europeâ&#x20AC;&#x2122;s industry in a strong IPR position.

NANO

Innovative tools for Graphene research

Visit our booth To find out more about how a partnership with Oxford Instruments can unlock challenging possibilities, please contact info.plc@oxinst.com

www.oxford-instruments.com/graphene

We are opening up the exciting world of graphene with our innovative toolbox of techniques and products, helping our partners to reveal even more of the nano-world.

SPONSORS

(Image courtesy of the Sunday Times)

Oxford Instruments delivers high tech tools and systems to support nanotechnology research.

Prof Sir Andre Geim and Prof Sir Konstantin Novoselov won a Nobel prize for their discovery of graphene. Oxford Instrumentsâ&#x20AC;&#x2122; tools played a key role in their research.

Exhibitors

advanced

graphene analysis Advanced materials offer unique properties linked to their physical forms and structures. Whether your project requires the analytical power of the Thermo Scientific DXR Raman microscope or the surface analysis capabilities of the Thermo Scientific K-Alpha XPS we combine research-grade performance with unmatched ease of use into one of the most productive tools available for materials science.

EXHIBITORS

â&#x20AC;˘ see the full capabilities at thermoscientific.com/carbon

unparalleled ease

Graphene Systems World leading supplier: Equipment for research and production. Monolayer Graphene

28 years in research: More than 2000 systems delivered.

EXHIBITORS

Technologies: CVD · PECVD · MOCVD · ALD · OVPD Multilayer Graphene

Applications: Electronics · Lighting · Storage · Energy

AIXTRON SE · Website: www.aixtron.com · Email: info@aixtron.com Aachen (Germany) · Cambridge (UK) · Sunnyvale (USA) · Lund (Sweden) · Seoul (Korea) Tokyo (Japan) · Shanghai (China) - Hsinchu (Taiwan)

Russia Pavilion

AkKoLab

EXHIBITORS

ABSTRACTS

Abstracts - Index

Plenary Speakers

PAGE Albert Fert (Université Paris Sud & CNRS/Thales, France) "Graphene and Spintronics"

Keynote Speakers

Eva Y. Andrei (Rutgers University, USA)

–

Mildred S. Dresselhaus (MIT, USA)

–

Klaus Mullen (MPI for Polymer Research, Germany) "Is the Future Black? – The Chemist’s Search for Graphene and Carbon Materials"

138

Invited Speakers

Li Baowen (National University of Singapore, Singapore) "Anomalous thermal transport in low dimensional nanostructures"

Johann Coraux (Institut Néel – CNRS, France) "Epitaxial graphene/metal hybrids"

64 72

Michael S. Fuhrer (University of Maryland, USA) "Broadband Photodetection with Graphene Devices"

Francisco Guinea (ICMM-CSIC, Spain) "Interaction effects in graphene heterostructures"

Masataka Hasegawa (AIST, Japan) Byung Hee Hong (Seoul National University, Korea) "Production and Applications of Graphene for Large-Area Electronics" Frank Koppens (ICFO, Spain) "Graphene: a novel platform for capturing and manipulating light at the nanoscale"

–

95 109

ABSTRACTS - INDEX

Toshiaki Enoki (Tokyo Institute of Technology, Japan) "Magnetic and electronic structures of nanographene and fluorinated nanographene with an interplay of edge-state spins and dangling bond spins" Jean-Noël Fuchs (Université Paris Sud, France) "Bloch-Zener oscillations as a probe of Dirac points merging in artificial graphene"

Nicola Marzari (EPFL, Switzerland) "Phonon lifetimes, thermal transport, and mobility in graphene from density-functional perturbation theory" Bae Ho Park (Konkuk University, Korea) "Characterization and manipulation of graphene using AFM"

146

Maurizio Prato (University of Trieste, Italy) "Reactivity of Graphene Sheets: Cycloadditions and Rolling up to form Nanotubes"

150

Christian Schönenberger (Basel University / SNI, Switzerland) "Gapped ground state in suspended bilayer graphene"

164

Jurgen Smet (Max Planck Institute for Solid State Research, Germany) Kazu Suenaga (AIST, Japan) "Atomic Imaging and Spectroscopy of Single Layered Materials with Interrupted Periodicities" Mauricio Terrones (The Pennsylvania State University, USA)

–

175 –

Graphene Flagship session

Invited Speakers

Vladimir Falko (Lancaster University, United Kingdom) "The Graphene Science and Technology Roadmap"

Andrea Ferrari (University of Cambridge, United Kingdom) "The Graphene Science and Technology Roadmap"

Masataka Hasegawa (AIST, Japan) "Japanese Graphene Research Activities and Roadmap" Byung Hee Hong (Seoul National Univ., Korea) "Korean Graphene Research Activities and Roadmap"

ABSTRACTS - INDEX

Jari Kinaret (Chalmers University of Technology, Sweden) “Graphene Flagship: working together to combine scientific excellence and technological impacts”

–

96 –

Orals Plenary

Adrien Allain (CNRS, France) "Tunable superconductivity in graphene based hybrid devices"

Christian Benz (Karlsruhe Inst. of Technology (KIT), Inst. of Nanotechnology (INT), Germany) "Graphene Field-Effect Transistors on Hexagonal Boron Nitride Operating at Microwave Frequencies"

Alexey Bezryadin (University of Illinois, United States) "Standard deviation of the switching supercurrent in graphene proximity junctions"

Liam Britnell (University of Manchester, United Kingdom) "Field-effect tunneling transistor based on vertical graphene heterostructures"

Alessandro Cresti (IMEP-LAHC (UMR 5130), France) "Quenching of the quantum Hall effect in graphene with scrolled edges"

Tim Echtermeyer (University of Cambridge, United Kingdom) "Photo-thermo- vs. photo-electric effects in metal-graphene-metal photodetectors"

Luis Foa Torres (FaMAF, Universidad Nacional de Córdoba, Argentina) "Tuning the transport properties of graphene through AC fields"

David Horsell (University of Exeter, United Kingdom) "Scattering mechanisms that cause 1/f noise in graphene"

100

Allen Hsu (MIT, United States) "Impact of Short Range Scattering in Graphene Electronics"

101

Antti-Pekka Jauho (Technical University of Denmark, Denmark) "Transport phenomena in nanostructured graphene"

105

Samuel Lara-Avila (Chalmers University of Technology, Sweden) "Disordered Fermi Liquid in Epitaxial Graphene from Quantum Transport Measurements"

115

Emiliano Pallecchi (Laboratoire de Photonique et Nanoastuctures, France) "Quantum Hall measurements on epitaxial graphene with oxygen adsorption"

145

Antoine Reserbat-Plantey (Institut Néel- CNRS, France) "A local optical probe for measuring motion and stress in a nanoelectromechanical system"

155

Biplab Sanyal (Uppsala University, Sweden) "Spin manipulation of organometallics by strain engineering of defected graphene"

157

Timo Schumann (Paul-Drude-Institut für Festkörperelektronik, Germany) "Anisotropic quantum Hall effect in graphene on stepped SiC surfaces"

165

Jean-Yves Veuillen (Institut Néel, CNRS-UJF, France) "Reconstruction Dependent Interaction at the Graphene/ 6H-SiC(000-1) Interface probed by STM and ab-initio calculations."

186

Heiko B. Weber (University of Erlangen, Germany) "Manifestation of electron-electron interaction in the magnetoresistance of graphene"

192

ABSTRACTS - INDEX

Andreas Betz (Ecole Normale Supérieure, France) "Electronic Cooling by 2D Acoustic Phonons in Graphene"

Parallel Workshop 1: Graphene Chemistry & Materials

Invited Speakers

Manish Chhowalla (Rutgers, USA) "Solution Processable Graphene and Other Two Dimensional Materials for Energy Applications" Mark C. Hersam (Northwestern University, USA) "Preparation and Application of Chemically Functionalized Graphene"

56 97

Renato Liardo (Volvo Corporate Materials Technology) "Cheap competitors of graphene -the actual use of carbon black and carbon fibres in the automotive and consumer industry"

121

Alain Pénicaud (University of Bordeaux, France) "Chemical Solutions to Exfoliate Graphite"

149

Paolo Samorì (ISIS - Universitè de Strasbourg & CNRS, France) "Supramolecular chemistry and (nano)graphenes: a honeymoon?"

156

ABSTRACTS - INDEX

Orals

Alexander Obraztsov (MV Lomonosov Moscow State University, Russia) "Graphene-based nanomaterials for field emission applications"

141

Vincenzo Palermo (CNR Bologna, Italy) "Introduction"

144

Vittorio Pellegrini (NEST, Italy) "Reversible Hydrogen Storage by Controlled Buckling of Graphene Layers"

148

Guido Saracco (Polytecnic of Turin, FIAT, IIT, Italy) "Potential of thermally conductive polymers based on carbon allotropes in the development of new heat management components on board a car"

159

Matthias Schwab (BASF SE, Germany) "Graphene Technology Platform at BASF"

167

Ester Vazquez (University of Castilla La Mancha, Spain) "Few-layer graphenes from ball-milling of graphite with triazine derivatives"

184

Parallel Workshop 2: Modelling and Simulation of Graphene-based Materials and Devices

Tutorial

Vladimir Falko (Lancaster University, United Kingdom)

–

Invited Speakers

Gianluca Fiori (University of Pisa, Italy) "Performance assessment of graphene-based devices through a multi-scale approach"

Arkady Krasheninikov (University of Helsinki and Aalto University, Finland) "Tailoring the properties of graphene, dichalcogenides and other 2D materials through electron irradiation: insight from DFT simulations and TEM experiments"

112

Aurélien Lherbier (Université Catholique de Louvain, Belgium) "Simulation of electronic transport in defective graphene. From point defects to amorphous structures"

119

Young-Woo Son (KIAS, Korea)

–

Dario Bercioux (Freiburg Institute for Advanced Studies, Germany) "Spin-Resolved Transport Properties of Inhomogeneous Graphene Nanostructures"

Anders Blom (QuantumWise A/S, Denmark) "Atomic-scale model for the contact resistance of the nickel-graphene interface"

Andres Rafael Botello Méndez (Université catholique de Louvain, Belgium) "Boron and nitrogen doping of graphene from first principles"

Johan Carlsson (Accelrys Ltd, United Kingdom) "Theory and hierarchical modeling of defective graphene, the effects of grain boundaries and oxidation"

Mairbek Chshiev (Spintec, CEA/CNRS/UJF-Grenoble, INAC, France) "Inducing magnetism in graphene in a view of spintronics"

Mauro Ferreira (Trinity College Dublin, Ireland) "Dynamic RKKY interaction in graphene"

Inanc Adagideli (Sabanci University, Turkey) "Edge effects in graphene nanostructures: spectral density and quantum transport"

ABSTRACTS - INDEX

Orals

Avik Ghosh (University of Virginia, United States) "Graphene based electronics and electron ‘optics’: quantum transport and device opportunities"

Pekka Koskinen (University of Jyväskylä, Finland) "Twisting Graphene Nanoribbons into Carbon Nanotubes"

111

Yury Lozovik (Institute of Spectroscopy, Russia) "Collective properties of Dirac electrons in graphene"

124

Elisa Molinari (University of Modena e Reggio Emilia, Italy) "Optical Excitations and Nanoplasmonics in Graphene Flakes and Ribbons"

134

Vittorio Morandi (CNR-IMM Bologna, Italy) "Folds and buckles at the nanoscale: experimental and theoretical investigation of the bending properties of graphene membranes"

135

Elena Sheka (Peoples Friendship University of Russia, Russia) "Correlation of odd electrons in graphene: Effect on chemistry, magnetism, and mechanics”

170

Maxim Trushin (University of Regensburg, Germany) "Photocurrent in graphene n-n' junctions"

182

Shengjun Yuan (Radboud University of Nijmegen, Netherlands) "Modeling Electronic Properties of Single-layer and Multilayer Graphene"

193

Xi Zhang (Nanyang Technological University, Singapore) "Selective generation of Dirac-Fermi polarons at graphene edges and atomic vacancies"

197

Parallel Workshop 3: Synthesis and Characterization of Graphene

Tutorial

Ute Kaiser (Ulm University, Germany)

–

ABSTRACTS - INDEX

Invited Speakers

Jérome Lagoute (Univ. Paris 7, France) "Electronic properties of nitrogen doped graphene measured at the atomic scale"

114

Wencai Ren (Institute of Metal Research, Chinese Academy of Sciences, China) "CVD Growth and Applications of Graphene with Millimetre-Size Single-Crystal Grains and Three-Dimensional Interconnected Graphene Networks"

153

Amina Taleb (Synchroton Soleil, France) "Linear band dispersion in multilayer epitaxial graphene grown on the SiC(000-1) C face"

179

Jamie Warner (University of Oxford, United Kingdom) "Defects, Dislocations and Disorder in Graphene at the Atomic Level"

190

Timothy Booth (DTU Nanotech, Denmark) "Channeling of graphene in environmental TEM: towards zero-disorder nanolithography"

Jessica Campos-Delgado (UniversitĂŠ catholique de Louvain, Belgium) "Graphene synthesis using alcohol precursors"

Jean-FranĂ§ois Colomer (University of Namur (FUNDP), Belgium) "Graphene synthesized by Atmospheric Pressure Chemical Vapour Deposition"

Malcolm Connolly (National Physical Laboratory, United Kingdom) "Charge writing on graphene devices using low temperature scanning probe microscopy"

Zheng Han (NEEL Institute, CNRS, France) "Mechanism of Growth of Graphene Grains on Copper during Low Pressure Chemical Vapor Deposition"

Robert Hurt (Brown University, United States) "Self-Assembled Graphene Nanosacks"

103

Martin Kalbac (UFCH JH, Czech Republic) "Raman spectroscopy of electrochemically doped 1-LG and 2-LG"

106

Philipp Leicht (University of Konstanz, Germany) "Tailoring the atomic structure and electronic properties of graphene/metal interfaces by intercalation"

117

Maria Losurdo (Italian National Council of Research-CNR, Italy) "Interfacial Chemical-Electrical-Optical Phenomena in CVD-Graphene/Metal Hybrids"

122

Thomas Michely (II. Physikalisches Insitut, Germany) "Europium on graphene: phase coexistence of clusters and islands"

131

Markus Morgenstern (RWTH Aachen, Germany) "Scanning Probe Microscopy on Graphene Quantum Dots"

137

Louis Nilsson (University of Aarhus, Denmark) "Graphene on the reconstructed Pt(100) surface and its interaction with atomic hydrogen"

139

Renald Schaub (University of St Andrews, United Kingdom) "Size-Selective Carbon Nanoclusters as Precursors to the Growth of Epitaxial Graphene"

161

Alexander Soldatov (Lulea University of Technology, Sweden) "Free standing graphene monolayer at high hydrostatic pressure"

172

Aldo Zarbin (Federal University of Parana, Brazil) "Tri-layer enriched graphene sample by mechanochemical exfoliation of graphite: A one-step route for the production, processing and deposition as transparent films" Amaia Zurutuza (Graphenea, Spain) "Graphene films synthesized via CVD"

195 199

Mark Boneschanscher (Utrecht University, Debye Institute for Nanomaterials Science, CMI, Netherlands) "The atomic and electronic structure of well-defined graphene nanoribbons by scanning probe microscopy"

ABSTRACTS - INDEX

Orals

Parallel Workshop 4: Applications of Graphene-based Materials

Invited Speakers

Tamara Blanco-Varela (AIRBUS, Spain) Stefano Borini (Nokia Research Center, United Kingdom) "Graphene technology for future mobile devices" Luigi Colombo (Texas Instruments, United States) Chun-Yung Sung (IBM, United States) "Near 400 GHz World Fastest Graphene RF Transistor For High Frequency Nanoelectronics and Circuits CMOS Platform Integration"

–

47 –

177

Orals

Francesco Bonaccorso (Cambridge University, United Kingdom) "Exfoliation and Sorting of Graphite flakes and inorganic two-dimensional materials"

Gordon Chiu (Grafoid Inc., Canada) "Applications of Graphene-based Materials"

Jesus de la Fuente (GRAPHENEA S.A, Spain) "Applications for Graphene films: market trends"

Vincent Derycke (CEA, France) "Flexible GHz Transistors Derived from Solution-Based Single-Layer Graphene"

Jose A. Garrido (Technische Universität München, Germany) "Graphene field effect transistors for bioelectronic applications"

ABSTRACTS - INDEX

Marcos Ghislandi (Eindhoven University of Technology, Netherlands) "Preparation routes to aqueous graphene dispersions and their influence on electrical conductivity of polymer composites" Filippo Giubileo (CNR-SPIN, Italy) "Study of double dip in the transfer characteristics of graphene based field-effect transistors" Neil Graddage (Swansea University, United Kingdom) "Roll to Roll Printing of Aqueous Pristine Graphene Dispersions" Stefan Hertel (University of Erlangen, Germany) "Tayloring the graphene/silicon carbide interface: a material system for monolithic waferscale electronics" Alexander Klekachev (IMEC, Belgium) "Graphene – CdSe/ZnS quantum dots conjugated systems: charge transfer phenomena and their applications" Christy Martin (Vorbeck Materials Corp, United States) "Near term commercial opportunities and applications of graphene"

85 89 90 98 107 126

Javier Martinez (ISOM Instituto de Sistemas Optoelectronicos y Microtecnologia, Spain) "Graphene Electrodes For Nano-LEDs"

127

CĂŠsar Merino (GRAnPH Nanotech/Grupo Antolin-Ingenieria, Spain) "Large crystalline graphene oxide sheets from helical ribbon carbon nanofibres"

129

Sergey Mikhailov (University of Augsburg, Germany) "Graphene Based Terahertz Emitter"

133

Elena Obraztsova (Prokhorov General Physics Institute, RAS, Russia) "Graphene for laser applications"

141

Antonio Radoi (IMT-Bucharest, Romania) "MSM photodetector based on gold decorated graphene ink"

151 162 168

Ken Teo (AIXTRON Ltd., United Kingdom) "Observing early stages of growth and scaling graphene over 300mm wafers"

180

Mercedes Vila (Universidad Complutense de Madrid, Spain) "Cell uptake survey of functionalized Graphene for Near-Infrared Mediated tumor Hyperthermia"

188

ABSTRACTS - INDEX

173

Marek Schmidt (University of Southampton, United Kingdom) "Large Area Plasma-Enhanced Chemical Vapor Deposition of Nanocrystalline Graphite on Insulator for Electronic Device Application" Udo Schwalke (Institute for Semiconductor Technology and Nanoelectronics (ISTN), Technische UniversitĂ¤t Darmstadt, Germany) "Transfer-Free Grown Bilayer Graphene Transistors with Ultra-High On/Off-Current Ratio" Roman Sordan (Politecnico di Milano, Italy) "Graphene audio voltage amplifier"

Abstracts – Index Alphabetical Order Workshop 1: Graphene Chemistry & Materials Workshop 2: Modelling and Simulation of Graphene-based Materials and Devices Workshop 3: Synthesis and Characterization of Graphene Workshop 4: Applications of Graphene-based Materials GFS: Graphene Flagship session

PAGE Inanc Adagideli (Sabanci University, Turkey) "Edge effects in graphene nanostructures: spectral density and quantum transport"

ORAL Workshop 2

Adrien Allain (CNRS, France) "Tunable superconductivity in graphene based hybrid devices"

ORAL Plenary Session

Eva Y. Andrei (Rutgers University, USA)

KEYNOTE Plenary Session

–

Li Baowen (National University of Singapore, Singapore) "Anomalous thermal transport in low dimensional nanostructures"

INVITED Plenary Session

Christian Benz (Karlsruhe Inst. of Technology (KIT), Inst. of Nanotechnology (INT), Germany) "Graphene Field-Effect Transistors on Hexagonal Boron Nitride Operating at Microwave Frequencies"

ORAL Plenary Session

ORAL Workshop 2

Andreas Betz (Ecole Normale Supérieure, France) "Electronic Cooling by 2D Acoustic Phonons in Graphene"

ORAL Plenary Session

Alexey Bezryadin (University of Illinois, United States) "Standard deviation of the switching supercurrent in graphene proximity junctions"

ORAL Plenary Session

Tamara Blanco-Varela (AIRBUS, Spain)

INVITED Workshop 4

–

Anders Blom (QuantumWise A/S, Denmark) "Atomic-scale model for the contact resistance of the nickel-graphene interface"

ORAL Workshop 2

Francesco Bonaccorso (Cambridge University, United Kingdom) "Exfoliation and Sorting of Graphite flakes and inorganic two-dimensional materials"

ORAL Workshop 4

Mark Boneschanscher (Utrecht Univ., Debye Inst. for Nanomaterials Science, CMI, Netherlands) "The atomic and electronic structure of well-defined graphene nanoribbons by scanning probe microscopy”

ORAL Workshop 3

Timothy Booth (DTU Nanotech, Denmark) "Channeling of graphene in environmental TEM: towards zero-disorder nanolithography"

ORAL Workshop 3

Stefano Borini (Nokia Research Center, United Kingdom) "Graphene technology for future mobile devices"

INVITED Workshop 4

Andres Rafael Botello Méndez (Université catholique de Louvain, Belgium) "Boron and nitrogen doping of graphene from first principles"

ORAL Workshop 2

ORAL Plenary Session

ORAL Workshop 3

ABSTRACTS - INDEX

Dario Bercioux (Freiburg Institute for Advanced Studies, Germany) "Spin-Resolved Transport Properties of Inhomogeneous Graphene Nanostructures"

Liam Britnell (University of Manchester, United Kingdom) "Field-effect tunneling transistor based on vertical graphene heterostructures" Jessica Campos-Delgado (Université Catholique de Louvain, Belgium) "Graphene synthesis using alcohol precursors"

Johan Carlsson (Accelrys Ltd, United Kingdom) "Theory and hierarchical modeling of defective graphene, the effects of grain boundaries and oxidation"

ORAL Workshop 2

Manish Chhowalla (Rutgers, USA) "Solution Processable Graphene and Other Two Dimensional Materials for Energy Applications"

INVITED Workshop 1

Gordon Chiu (Grafoid Inc., Canada) "Applications of Graphene-based Materials"

ORAL Workshop 4

Mairbek Chshiev (Spintec, CEA/CNRS/UJF-Grenoble, INAC, France) "Inducing magnetism in graphene in a view of spintronics"

ORAL Workshop 2

Luigi Colombo (Texas Instruments, United States)

INVITED Workshop 4

–

Jean-François Colomer (University of Namur (FUNDP), Belgium) "Graphene synthesized by Atmospheric Pressure Chemical Vapour Deposition"

ORAL Workshop 3

Malcolm Connolly (National Physical Laboratory, United Kingdom) "Charge writing on graphene devices using low temperature scanning probe microscopy"

ORAL Workshop 3

Johann Coraux (Institut Néel – CNRS, France) "Epitaxial graphene/metal hybrids"

INVITED Plenary Session

Alessandro Cresti (IMEP-LAHC (UMR 5130), France) "Quenching of the quantum Hall effect in graphene with scrolled edges"

ORAL Plenary Session

Jesus de la Fuente (Graphenea, Spain) "Applications for Graphene films: market trends"

ORAL Workshop 4

Vincent Derycke (CEA, France) "Flexible GHz Transistors Derived from Solution-Based Single-Layer Graphene"

ORAL Workshop 4

Mildred S. Dresselhaus (MIT, USA)

KEYNOTE Plenary Session

–

Tim Echtermeyer (University of Cambridge, United Kingdom) "Photo-thermo- vs. photo-electric effects in metal-graphene-metal photodetectors"

ORAL Plenary Session

Toshiaki Enoki (Tokyo Institute of Technology, Japan) "Magnetic and electronic structures of nanographene and fluorinated nanographene with an interplay of edge-state spins and dangling bond spins"

INVITED Plenary Session

Vladimir Falko (Lancaster University, United Kingdom) "The Graphene Science and Technology Roadmap"

INVITED GFS

Andrea Ferrari (University of Cambridge, United Kingdom) "The Graphene Science and Technology Roadmap"

INVITED GFS

ORAL Workshop 2

Plenary Speaker

INVITED Workshop 2

Luis Foa Torres (FaMAF, Universidad Nacional de Córdoba, Argentina) "Tuning the transport properties of graphene through AC fields"

ORAL Plenary Session

Jean-Noël Fuchs (Université Paris Sud, France) "Bloch-Zener oscillations as a probe of Dirac points merging in artificial graphene"

INVITED Plenary Session

Michael S. Fuhrer (University of Maryland, USA) "Broadband Photodetection with Graphene Devices"

INVITED Plenary Session

Gianluca Fiori (University of Pisa, Italy) "Performance assessment of graphene-based devices through a multi-scale approach"

ABSTRACTS - INDEX

Albert Fert (Université Paris Sud & CNRS/Thales, France) "Graphene and Spintronics"

Mauro Ferreira (Trinity College Dublin, Ireland) "Dynamic RKKY interaction in graphene"

Jose A. Garrido (Technische Universität München, Germany) "Graphene field effect transistors for bioelectronic applications"

ORAL Workshop 4

Marcos Ghislandi (Eindhoven University of Technology, Netherlands) "Preparation routes to aqueous graphene dispersions and their influence on electrical conductivity of polymer composites"

ORAL Workshop 4

Avik Ghosh (University of Virginia, United States) "Graphene based electronics and electron ‘optics’: quantum transport and device opportunities"

ORAL Workshop 2

Filippo Giubileo (CNR-SPIN, Italy) "Study of double dip in the transfer characteristics of graphene based field-effect transistors"

ORAL Workshop 4

Neil Graddage (Swansea University, United Kingdom) "Roll to Roll Printing of Aqueous Pristine Graphene Dispersions"

ORAL Workshop 4

INVITED Plenary Session

ORAL Workshop 3

Masataka Hasegawa (AIST, Japan) "Japanese Graphene Research Activities and Roadmap"

INVITED GFS

–

Byung Hee Hong (Seoul National Univ., Korea) "Korean Graphene Research Activities and Roadmap"

INVITED GFS

Byung Hee Hong (Seoul National University, Korea) "Production and Applications of Graphene for Large-Area Electronics"

INVITED Plenary Session

Mark C. Hersam (Northwestern University, USA) "Preparation and Application of Chemically Functionalized Graphene"

INVITED Workshop 1

Stefan Hertel (University of Erlangen, Germany) "Tayloring the graphene/silicon carbide interface: a material system for monolithic wafer-scale electronics"

ORAL Workshop 4

David Horsell (University of Exeter, United Kingdom) "Scattering mechanisms that cause 1/f noise in graphene"

ORAL Plenary Session

100

Allen Hsu (MIT, United States) "Impact of Short Range Scattering in Graphene Electronics"

ORAL Plenary Session

101

ORAL Workshop 3

103

ORAL Plenary Session

105

Ute Kaiser (Ulm University, Germany)

INVITED Workshop 3

–

Martin Kalbac (UFCH JH, Czech Republic) "Raman spectroscopy of electrochemically doped 1-LG and 2-LG"

ORAL Workshop 3

106

INVITED GFS

–

ORAL Workshop 4

107

INVITED Plenary Session

109

ORAL Workshop 2

111

Francisco Guinea (ICMM-CSIC, Spain) "Interaction effects in graphene heterostructures" Zheng Han (NEEL Institute, CNRS, France) "Mechanism of Growth of Graphene Grains on Copper during Low Pressure Chemical Vapor Deposition"

Robert Hurt (Brown University, United States) "Self-Assembled Graphene Nanosacks"

ABSTRACTS - INDEX

Antti-Pekka Jauho (Technical University of Denmark, Denmark) "Transport phenomena in nanostructured graphene"

Jari Kinaret (Chalmers University of Technology, Sweden) “Graphene Flagship: working together to combine scientific excellence and technological impacts” Alexander Klekachev (IMEC, Belgium) "Graphene – CdSe/ZnS quantum dots conjugated systems: charge transfer phenomena and their applications" Frank Koppens (ICFO, Spain) "Graphene: a novel platform for capturing and manipulating light at the nanoscale" Pekka Koskinen (University of Jyväskylä, Finland) "Twisting Graphene Nanoribbons into Carbon Nanotubes"

112

Jérome Lagoute (Univ. Paris 7, France) "Electronic properties of nitrogen doped graphene measured at the atomic scale"

INVITED Workshop 3

114

Samuel Lara-Avila (Chalmers University of Technology, Sweden) "Disordered Fermi Liquid in Epitaxial Graphene from Quantum Transport Measurements"

ORAL Plenary Session

115

Philipp Leicht (University of Konstanz, Germany) "Tailoring the atomic structure and electronic properties of graphene/metal interfaces by intercalation"

ORAL Workshop 3

117

Aurélien Lherbier (Université Catholique de Louvain, Belgium) "Simulation of electronic transport in defective graphene. From point defects to amorphous structures"

INVITED Workshop 2

119

Renato Liardo (Volvo Corporate Materials Technology) "Cheap competitors of graphene -the actual use of carbon black and carbon fibres in the automotive and consumer industry"

INVITED Workshop 1

121

Maria Losurdo (Italian National Council of Research-CNR, Italy) "Interfacial Chemical-Electrical-Optical Phenomena in CVD-Graphene/Metal Hybrids"

ORAL Workshop 3

122

Yury Lozovik (Institute of Spectroscopy, Russia) "Collective properties of Dirac electrons in graphene"

ORAL Workshop 2

124

Christy Martín (Vorbeck Materials Corp, United States) "Near term commercial opportunities and applications of graphene"

ORAL Workshop 4

126

Javier Martínez (ISOM Instituto de Sistemas Optoelectronicos y Microtecnologia, Spain) "Graphene Electrodes For Nano-LEDs"

ORAL Workshop 4

127

INVITED Plenary Session

–

Cesar Merino (GRAnPH Nanotech/Grupo Antolin-Ingenieria, Spain) "Large crystalline graphene oxide sheets from helical ribbon carbon nanofibres"

ORAL Workshop 4

129

Thomas Michely (II. Physikalisches Insitut, Germany) "Europium on graphene: phase coexistence of clusters and islands"

ORAL Workshop 3

131

Sergey Mikhailov (University of Augsburg, Germany) "Graphene Based Terahertz Emitter"

ORAL Workshop 4

133

Elisa Molinari (University of Modena e Reggio Emilia, Italy) "Optical Excitations and Nanoplasmonics in Graphene Flakes and Ribbons"

ORAL Workshop 2

134

Vittorio Morandi (CNR-IMM Bologna, Italy) "Folds and buckles at the nanoscale: experimental and theoretical investigation of the bending properties of graphene membranes"

ORAL Workshop 2

135

Markus Morgenstern (RWTH Aachen, Germany) "Scanning Probe Microscopy on Graphene Quantum Dots"

ORAL Workshop 3

137

KEYNOTE Plenary Session

138

Louis Nilsson (University of Aarhus, Denmark) "Graphene on the reconstructed Pt(100) surface and its interaction with atomic hydrogen"

ORAL Workshop 3

139

Alexander Obraztsov (MV Lomonosov Moscow State University, Russia) "Graphene-based nanomaterials for field emission applications"

ORAL Workshop 1

141

Nicola Marzari (EPFL, Switzerland) "Phonon lifetimes, thermal transport, and mobility in graphene from density-functional perturbation theory"

Klaus Mullen (MPI for Polymer Research, Germany) "Is the Future Black? – The Chemist’s Search for Graphene and Carbon Materials"

ABSTRACTS - INDEX

INVITED Workshop 2

Elena Obraztsova (Prokhorov General Physics Institute, RAS, Russia) "Graphene for laser applications"

ORAL Workshop 4

143

Vincenzo Palermo (CNR Bologna, Italy) "Introduction"

ORAL Workshop 1

144

Emiliano Pallecchi (Laboratoire de Photonique et Nanoastuctures, France) "Quantum Hall measurements on epitaxial graphene with oxygen adsorption"

ORAL Plenary Session

145

Bae Ho Park (Konkuk University, Korea) "Characterization and manipulation of graphene using AFM"

INVITED Plenary Session

146

Vittorio Pellegrini (NEST, Italy) “Reversible Hydrogen Storage by Controlled Buckling of Graphene Layers"

ORAL Workshop 1

148

Alain Pénicaud (University of Bordeaux, France) "Chemical Solutions to Exfoliate Graphite"

INVITED Workshop 1

149

INVITED Plenary Session

150

Antonio Radoi (IMT-Bucharest, Romania) "MSM photodetector based on gold decorated graphene ink"

ORAL Workshop 4

151

Wencai Ren (Institute of Metal Research, Chinese Academy of Sciences, China) "CVD Growth and Applications of Graphene with Millimetre-Size Single-Crystal Grains and ThreeDimensional Interconnected Graphene Networks"

INVITED Workshop 3

153

ORAL Plenary Session

155

INVITED Workshop 1

156

ORAL Plenary Session

157

Guido Saracco (Polytecnic of Turin, FIAT, IIT, Italy) "Potential of thermally conductive polymers based on carbon allotropes in the development of new heat management components on board a car"

ORAL Workshop 1

159

Renald Schaub (University of St Andrews, United Kingdom) "Size-Selective Carbon Nanoclusters as Precursors to the Growth of Epitaxial Graphene"

ORAL Workshop 3

161

Marek Schmidt (University of Southampton, United Kingdom) "Large Area Plasma-Enhanced Chemical Vapor Deposition of Nanocrystalline Graphite on Insulator for Electronic Device Application"

ORAL Workshop 4

162

Christian Schönenberger (Basel University / SNI, Switzerland) "Gapped ground state in suspended bilayer graphene"

INVITED Plenary Session

164

Timo Schumann (Paul-Drude-Institut für Festkörperelektronik, Germany) "Anisotropic quantum Hall effect in graphene on stepped SiC surfaces"

ORAL Plenary Session

165

Matthias Schwab (BASF SE, Germany) "Graphene Technology Platform at BASF"

ORAL Workshop 1

167

Udo Schwalke (Institute for Semiconductor Technology and Nanoelectronics (ISTN), Technische Universität Darmstadt, Germany) "Transfer-Free Grown Bilayer Graphene Transistors with Ultra-High On/Off-Current Ratio"

ORAL Workshop 4

168

Elena Sheka (Peoples Friendship University of Russia, Russia) "Correlation of odd electrons in graphene: Effect on chemistry, magnetism, and mechanics"

ORAL Workshop 2

170

INVITED Plenary Session

–

Maurizio Prato (University of Trieste, Italy) "Reactivity of Graphene Sheets: Cycloadditions and Rolling up to form Nanotubes"

Antoine Reserbat-Plantey (Institut Néel- CNRS, France) "A local optical probe for measuring motion and stress in a nanoelectromechanical system" Paolo Samorì (ISIS - Universitè de Strasbourg & CNRS, France) "Supramolecular chemistry and (nano)graphenes: a honeymoon?"

ABSTRACTS - INDEX

Biplab Sanyal (Uppsala University, Sweden) "Spin manipulation of organometallics by strain engineering of defected graphene"

Jurgen Smet (Max Planck Institute for Solid State Research, Germany)

172

Young-Woo Son (KIAS, Korea)

INVITED Workshop 2

–

Roman Sordan (Politecnico di Milano, Italy) "Graphene audio voltage amplifier"

ORAL Workshop 4

173

Kazu Suenaga (AIST, Japan) "Atomic Imaging and Spectroscopy of Single Layered Materials with Interrupted Periodicities"

ORAL Plenary Session

175

Chun-Yung Sung (IBM, United States) "Near 400 GHz World Fastest Graphene RF Transistor For High Frequency Nanoelectronics and Circuits CMOS Platform Integration"

INVITED Workshop 4

177

Amina Taleb (Synchroton Soleil, France) "Linear band dispersion in multilayer epitaxial graphene grown on the SiC(000-1) C face"

INVITED Workshop 3

179

Ken Teo (AIXTRON Ltd., United Kingdom) "Observing early stages of growth and scaling graphene over 300mm wafers"

ORAL Workshop 4

180

INVITED Plenary Session

–

Alessandro Tredicucci (NEST CNR-Nano and Scuola Normale Superiore Pisa, Italy)

ORAL Workshop 4

–

Maxim Trushin (University of Regensburg, Germany) "Photocurrent in graphene n-n' junctions"

ORAL Workshop 2

182

Ester Vazquez (University of Castilla La Mancha, Spain) "Few-layer graphenes from ball-milling of graphite with triazine derivatives"

ORAL Workshop 1

184

ORAL Plenary Session

186

Mercedes Vila (Universidad Complutense de Madrid, Spain) "Cell uptake survey of functionalized Graphene for Near-Infrared Mediated tumor Hyperthermia"

ORAL Workshop 4

188

Jamie Warner (University of Oxford, United Kingdom) "Defects, Dislocations and Disorder in Graphene at the Atomic Level"

INVITED Workshop 3

190

ORAL Plenary Session

192

Shengjun Yuan (Radboud University of Nijmegen, Netherlands) "Modeling Electronic Properties of Single-layer and Multilayer Graphene"

ORAL Workshop 2

193

ORAL Workshop 3

195

Xi Zhang (Nanyang Technological University, Singapore) "Selective generation of Dirac-Fermi polarons at graphene edges and atomic vacancies"

ORAL Workshop 2

197

Amaia Zurutuza (Graphenea, Spain) "Graphene films synthesized via CVD"

ORAL Workshop 3

199

Mauricio Terrones (The Pennsylvania State University, USA)

Jean-Yves Veuillen (Institut Néel, CNRS-UJF, France) "Reconstruction Dependent Interaction at the Graphene/ 6H-SiC(000-1) Interface probed by STM and ab-initio calculations"

Heiko B. Weber (University of Erlangen, Germany) "Manifestation of electron-electron interaction in the magnetoresistance of graphene"

ABSTRACTS - INDEX

ORAL Workshop 3

Alexander Soldatov (Lulea University of Technology, Sweden) "Free standing graphene monolayer at high hydrostatic pressure"

Edge effects in graphene nanostructures: spectral density and quantum transport

Inanc Adagideli, Juergen Wurm, Klaus Richter Sabanci University, Orhanli-Tuzla, Istanbul, Turkey adagideli@sabanciuniv.edu

We investigate the effect of different edge types on the statistical properties of both the energy spectrum of closed graphene billiards [1] and the conductance of open graphene cavities [2] in the semiclassical limit. To this end, we develop an exact expansion for the single particle Green's function of ballistic graphene structures in terms of multiple reflections from the system boundary, that allows for a natural treatment of edge effects. We first apply this formalism to calculate the average density of states of graphene billiards. While the leading term in the corresponding Weyl expansion is proportional to the billiard area, we find that the contribution that usually scales with the total length of the system boundary differs significantly from what one finds in semiconductor-based, Schr\"odinger type billiards: The latter term vanishes for armchair and infinite mass edges and is proportional to the zigzag edge length, highlighting the prominent role of zigzag edges in graphene. We then compute analytical expressions for the density of states oscillations and energy levels within a trajectory based semiclassical approach. We derive a Dirac version of Gutzwiller's trace formula for classically chaotic graphene billiards and further obtain semiclassical trace formulae for the density of states oscillations in regular graphene cavities. Next we study the spectral two point correlation function, or more precisely its Fourier transform the spectral form factor. We calculate the two leading order contributions to the spectral form factor, paying particular attention to the influence of the edge characteristics of the system. Then we consider transport properties of open graphene cavities. We derive generic analytical expressions for the classical conductance, the weak localization correction, the size of the universal conductance fluctuations and the shot noise power of a ballistic graphene cavity. Again we focus on the effects of the edge structure. For both, the conductance and the spectral prperties, we find that edge induced pseudospin interference affects the results significantly. In particular intervalley coupling mediated through scattering from armchair edges is the key mechanism that governs the coherent quantum interference effects in ballistic graphene cavities.an event.

References

ABSTRACTS

[1] Jürgen Wurm, Klaus Richter, and İnanç Adagideli Phys. Rev. B 84, (2011) 075468 [2] Jürgen Wurm, Klaus Richter, and İnanç Adagideli; Phys. Rev. B 84, (2011) 205421

Tunable superconductivity in graphene based hybrid devices

A. Allain , Z. Han , B. Kessler , C. Girit , A. Zettl , V. Bouchiat 1 2

Neel Institute, CNRS-Grenoble, France Physics Dept, University of California, Berkeley, CA, USA adrien.allain@grenoble.cnrs.fr

The easily accessible 2D electron gas in graphene provides an ideal platform on which to tune, via application of an electrostatic gate, the coupling between electronically ordered dopants deposited on its surface. I will present recent experimental studies on electrostatically tuned superconducting transition in graphene sheets decorated with tin nanoparticles. The transition towards superconducting state is due to percolation of superconductivity induced by proximity effect within the nanoparticules random array. Depending of the disorder within the graphene layer, superconductivity show different characteristics and significant variations. In case of low disorder exfoliated graphene, the superconducting state results from a Berezinski-Kosterlitz-Thouless transition which leads to an homogeneous 2D superconducting state [1]. In case of disordered Graphene (CVD-grown),we show that upon changes in carrier density (+/-7.1012 cm-2, applying a gate voltage), a transition from a superconducting to a truly insulating state can be induced. [2]. An intermediate metallic regime is also present at the transition showing sheet resistivity of the order of the resistance quantum h/4e^2. We interpret this transition within the framework of granular superconductivity found in Josephson junction arrays. The intense positive magnetoresistance observed for fields below the critical field of tin nanoparticles is a signature of the localization of Cooper pairs. This hybrid system appears to be an original platform to investigate the current understanding of the physics of the superconductor-insulator quantum phase transition and offer a original starting material for the realization of superconducting weak links.

References [1] B. M. Kessler et al., Phys. Rev. Lett. 104,047001 (2010). [2] A. Allain et al., http://arxiv.org/abs/1109.6910.

ABSTRACTS

Figures

Figure 1: Superconducting Metal-insulating transition induced in Tin doped Graphene: Left, micrograph of a typical sample, showing the macroscopic CVD-grown Graphene Sheet, Center :resistance-temperature curves at different gate voltages (gate step 5V) Right : Field effect at different temperature,showing the universal resistance at the transition.

Anomalous Thermal Transport in Low Dimensional Nanostructures

Li Baowen Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore 117542, Singapore Center for Phononics and Thermal Energy Science, Department of Physics, Tongji University, Shanghai 200092, People’s Republic of China phylibw@nus.edu.sg phononics@tongji.edu.cn

The study of thermal transport in low dimensional nano scale structures is important for both fundamental research and industrial applications. On the one hand, the low dimensional nanostructures such as graphene, nanowires, and nanotubes provide a test bed for the conjectures and hypothesis proposed in the last two decades for heat transport in two dimensional (2D) and one dimensional (1D) systems [1]. On the other hand, low dimensional nano structured materials have been found to be an ideal candidates to realize phononic functions such as thermal rectifier [2]. In bulk material, heat conduction is governed by Fourier’s law as: J=-κ∇T (1) where J is the local heat flux and ∇T the temperature gradient, κ is the thermal conductivity which is size independent. This is based on the assumption that phonons transport diffusively. However, for the low dimensional systems, in particular 1D systems, except for a simple harmonic oscillator chains, we don’t have any rigorous mathematical proof if the normal diffusion process can happen. Therefore it is still an open question whether the Fourier law is valid in 1D and 2D systems. Especially the sufficient and necessary condition for Fourier’s law is not clear yet [1]. In this talk, I will demonstrate that heat transfers in 1D and 2D systems are significantly from bulk material. (1) Both numerically and experimentally show that thermal conductivity in 1D and/or quasi 1D system such as nanowire and nanotube is not a constant. It depends on the system length as [3-4] (Fig 1 for silicon nanowire and Fig 2 for nanotube): κ∼Lβ, with 0< β <1. (2) Thermal conductivity in single layer suspended graphene depends on the length logarithmically when the width is fixed [5]. In the last part, I will present our recent mathematical theory which bridges the anomalous thermal conductivity to anomalous energy diffusion [9,10].

A Dhar, Adv. Phys. 57, 457 (2008). N.-B Li, J. Ren, L Wang, G Zhang, P Hanggi, and B Li, Rev. Mod. Phys, in press (2012) N. Yang, G. Zhang, and B. Li, Nano Today 5, 85 (2010). C W Chang, D Okawa, H Garcia, A Majumdar, and A Zettl, Phys. Rev. Lett. 101, 075903 (2008). X-F Xu et al Nature Materials (submitted) L Lindsay, D A Broido, and N Mingo, Phys. Rev. B 82, 115427 (2010). D L Nika, S Ghosh, E P Pokatilov, and A A Balandin, Appl. Phys. Lett. 94, 203103 (2009) L Yang, P Grassberger, and B Hu, Phys. Rev. E 74, 062101 (2006). B Li and L Wang, Phys. Rev. Lett 91, 044301 (2003). S Liu, J Ren, N.-B Li, and B Li, Phys. Rev. Lett (submitted)

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

ABSTRACTS

References

Figures

Figure 1: The dependence of thermal conductivity of SiNWs on the longitude length Lz. The results by Nose-Hoover method coincide with those by Langevin methods, indicating that the results are independent of the heat bath used. The black solid curves are the power law fitting curves (linear in log-log scale). For more details see Ref [3].

ABSTRACTS

Figure 2: Left: A SEM image of a thermal conductivity test fixture with a nanotube after five sequences of (CH3)3(CH3C5H4)Pt deposition. The numbers denote the nth deposition. The inset shows the SEM image after the first (CH3)3(CH3C5H4)Pt deposition. Right: Normalized thermal resistance vs normalized sample length for CNT (solid black circles), best fit assuming β=0.6 (open blue stars), and best fit assuming Fourier’s law (open red circles). For more details see Ref [4].

Figure 3: Length dependence of κ at room temperature (black solid circles) of single suspended graphene. The black linear line is a guide to the eyes. The black arrow and dashed line indicate the phonon mean free path. The red solid honeycombs and squares are plotted by extracting the data calculated by Lindsay el al.[6] and Nika et al.[7], respectively. Note that this ~ logL is only valid when L>> λ and deviations from ~ logL in the shortest samples is expected [8]. Insert: illustration of logκ ~ logL scaling behavior for 1D, 2D and 3D systems, where thermal conductivity scales as ~L0.3 , ~logL and constant, respectively.

Graphene Field-Effect Transistors on Hexagonal Boron Nitride Operating at Microwave Frequencies

1,2

Christian Benz, Zeineb Ben Aziza, Jens Mohrmann, Emiliano Pallecchi, Andreas Betz, 5 5 4 1,2,6 and Romain Kenji Watanabe, Takashi Taniguchi, Bernard Plaçais, Hilbert von Löhneysen, 1,2 Danneau 1

Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany Institute of Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany Laboratoire de Photonique et Nanostructures, CNRS, route de Nozay, 91460 Marcoussis, France 4 Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 24, rue Lhomond, 75231 Paris Cedex 05, France 5 National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan 6 Institute for Solid-State Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany c.benz@kit.edu 2 3

Due to its high charge carrier mobility, graphene is an ideal candidate for devices operating at microwave frequency [1-4]. Despite the typically low on-off ratio in graphene devices, they may perform well in analog applications. In radio-frequency graphene field-effect transistors (RF GFETs), transit frequencies up to 300 GHz have been reached4 and even basic integrated circuits were demonstrated [5,6]. We have investigated RF GFETs on hexagonal boron nitride (hBN). Boron nitride crystals are known to increase the mobility by reducing scattering in graphene, since they are atomically flat. At the same time, boron nitride serves as dielectric between the graphene sheet and pre-patterned gate electrode (schematics: fig. 1, optical micrograph: fig. 2). It has been shown that hBN acts as a defect-free dielectric [8]. The hBN flakes can be exfoliated down to few or even one atomic layer enabling very thin dielectrics. Thus, a minimum of charge impurities is introduced to the graphene. Moreover, current annealing remains possible since the graphene channel is not covered by an oxide. Our GFETs were prepared from exfoliated mono- and bi-layer graphene with a subsequent dry transfer technique. To improve the flatness of the flakes, we employed an all-graphene layout with graphene gate fingers in some of the devices. Losses due to the parasitic capacitances of the coplanar waveguide contacting pads we reduced using sapphire [9], a fully insulating substrate. Several devices with gate lengths down to 100 nm were produced and measured (fig. 3). Our manufacturing methods allow for integration of the graphene FETs into circuits like amplifiers or mixers. Together with the excellent heat conduction of sapphire they are well suited for cryogenic applications.

Meric, I. et al., IEDM 4796738 (2008) Lin, Y.-M. et al., Nano Lett. 9 (1) (2009) 422 Wu, Y. et al., Nature 472 (2011) 74-78 Liao, L. et al., Nature 467 (2010) 305 Lin, Y.-M. et al., Science, 332 (2011) 1294-1297 Han, S.-J. et al., Nano Lett. 11 (9) (2011) 3690–3693 Wang, H. et al., IEEE Electron Device Lett. 32 (99) (2011) 1-3 [8] Britnell, L. et al. arXiv 1202.0735 (2012) [9] Pallecchi, E et. al, Appl. Phys. Lett. 99, 113502 (2011)

[1] [2] [3] [4] [5] [6] [7] [8] [9]

ABSTRACTS

References

Figures

Figure 1: Crosscut schematics of the device layout.

Figure 2: Optical micrograph of one of the devices. In the center, the hexagonal boron nitride flake is visible. The inset shows the active area of the transistor in a GSG-layout with two finger gate.

1000

current gain |h21|

100

1 h21 h21 (de-embeded)

0,1 0,1

100

Frequency (GHz)

ABSTRACTS

Figure 3: Current gain vs. frequency for one of the devices with metallic gate.

Spin-Resolved Transport Properties of Inhomogeneous Graphene Nanostructures

Dario Bercioux Freiburg Institute for Advanced Studies, Albertstr. 19, 79104 Freiburg, Germany dario.bercioux@frias.uni-freiburg.de

We address the problem of spin-resolved scattering through spin-orbit nanostructures in single-layer graphene, i.e., regions of inhomogeneous spin-orbit coupling on the nanometer scale. Our main motivation stems from a recent experiment that reported a large enhancement of extrinsic or Rashba spinorbit coupling splitting in single-layer graphene grown on Ni(111) intercalated with a gold monolayer [1], and a recent theoretical proposal that shows how the presence of indium and thallium ad-atoms can enhance the gap associated to this intrinsic spin-orbit coupling [2]. In particular, we discuss the phenomenon of spin-double refraction and its consequences on the spin polarization. We study the transmission properties of a single, a double interface [3] and a periodic system [4] between a region without spin-orbit coupling – normal region – and a region with finite spin-orbit coupling – spin-orbit region. Furthermore, we analyze the polarization properties of these systems. In the case of the periodic system, the simple form of the band condition enables us to estimate the size of gaps due to avoided band crossings and gives insight into the dependence of the band-structure on the width of the potential. We also investigate band structures for the case where the lattice momentum forms a finite incidence angle with respect to the modulation direction of the spin-orbit coupling. Finally, we address the problem of spin and charge adiabatic quantum pumping in the presence of applied external gate voltages. We show that under particular conditions it is possible to find parameter regimes in which the charge current is negligible compared to the spin current [5].

References

ABSTRACTS

A. Varykhalov et al., Phys. Rev. Lett. 101, 157601 (2008). C. Weeks at al., Phys. Rev. X 1, 021001 (2011). D. Bercioux and A. De Martino, Phys. Rev. B 81, 165410 (2010). L. Lenz and D. Bercioux, EPL 96, 27006 (2011). D. Bercioux, D. F. Urban, F. Romeo, and R. Citro, (2012), submitted.

[1] [2] [3] [4] [5]

Electronic Cooling by 2D Acoustic Phonons in Graphene

Andreas Betz , F. Vialla , D. Brunel , C. Voisin , M. Picher , A. Cavanna , A. Madouri , G. Fève , 1 1 1 J.-M. Berroir , B. Plaçais and E. Pallecchi 1 2

Laboratoire Pierre Aigrain, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France Laboratoire de Photonique et Nanostructures, Route de Nozay, 91460 Marcoussis Cedex, France andreas.betz@lpa.ens.fr

We have investigated the energy relaxation of hot electrons in metallic graphene by means of noise thermometry. For this purpose, we have carried out GHz noise measurements at high bias voltage V and liquid helium temperature in various diffusive samples. These include CVD grown samples on Si/SiO2 substrate as well as graphene deposited on hexagonal boron nitride (hBN). Therein we measure the current noise spectral density SI as a function of frequency in the range of f=0--0.8GHz, which we are able to convert to electronic temperature Te. We observe Te proportional to V and proportional to square root of V at low and high bias, respectively. The first agrees with the electron-electron relaxation regime where heat conduction to the contacts is given by the Wiedemann-Franz law. The second corresponds to a Te4 dependence of the cooling power. It is the signature of a 2D acoustic phonon mechanism and the hallmark of layered conductors. In graphene, the observation of acoustic phonons is difficult due to their weak coupling and the strong effect of optical phonons. The interpretation above is confirmed by a theoretical analysis of the electron to phonon cooling crossover using the heat equation with a Σ* Te4phonon term. By solving the heat equation, assuming perfectly cold phonons, we find the spatial temperature profiles with respect to the incoming Joule power V2/R and the energy loss towards phonons, Σ* Te4. Via integration, we then obtain the average electron temperature Te as a function of applied bias V. Comparing data and theory, we deduce the coupling constant Σ, [1] which is smaller than theoretical predictions for LA-phonons [2]. For further analysis we will finally discuss our results in terms of Fano factor F=SI/2eI, a dimensionless quantity widely used to discuss electronic noise in mesoscopic physics. Here, I is the drain-source current. In general, the Fano factor will increase from 1/3 to √3/4, as a sign of electron-electron interactions, then decrease following a power law with increasing bias due to electron-phonon interactions.

ABSTRACTS

Overall, these measurements give new insight into electronic cooling mechanisms in graphene and can be helpful in the development of graphene based devices, such as graphene electronic sensors. References [1] [2]

A.C. Betz et al., to be published J.K. Viljas, T.T. Heikkilä, Phys. Rev. B 81, 245404 (2010).

Standard deviation of the switching supercurrent in graphene proximity junctions

Alexey Bezryadin, M. Brenner, U. C. Coskun, T. Hymel, J. Ku, V. Vakaryuk, A. Levchenko University of Illinois, 1110 W. Green str., Urbana, USA bezryadi@illinis.edu

Measurements of the decay statistics of metastable states is a powerful tool for revealing the intrinsic thermal and/or quantum fluctuations of the nano-scale system. In the Josephson junctions (JJ) a metastable dissipationless (superconducting) state decays into dissipative (phase slippage) state when the bias current, I, reaches so-called called switching current, Isw, which is stochastic. Analysis of the distribution of the switching current was employed to reveal macroscopic quantum tunnelling in magnetic nanoparticles, JJs, superconducting nanowires, and intrinsic JJs in high-T_c compounds. Experimentally observed temperature dependence of the switching current standard deviation, sigma, obtained by measuring the switching current many times on the same sample, always follows a power law, sigma~T^{2/3}, if the switching is induced by a single thermally activated escape from the metastable state. However, at sufficiently low temperatures, the temperature dependence of sigma saturates, which is usually attributed to macroscopic quantum tunnelling. In general, any power law different from 2/3 is associated with the possibility of quantum phase slips.

We find that the standard deviation, sigma, of the switching current distribution scales with temperature as sigma~T^alpha. The power, alpha, of the power law temperature dependence of the standard deviation can be as low as 1/3 in graphene junctions [1]. This observation is in sharp contrast with the known JJ behavior in which alpha=2/3, as predicted by Kurkijarvi [2]. We find an explanation to the observed unusual power alpha within the Kurkijarvi theory itself, which we modify appropriately to apply to our current-biased junctions. In fact, the power law in the theory is dependent not only on temperature by also on the critical current. In tunnel junctions with superconducting electrodes the critical current is not temperature dependent at low temperatures. But, in proximity junctions [3] (called superconductornormal-superconductor or SNS) the temperature dependence of the critical current persists, in theory, down to zero temperature. According to Kurkijarvi, sigma scales with the critical current as sigma~Ic^{1/3}. We check this explicitly, probably for the first time, using the gate voltage control, which allows us to vary Ic in a wide diapason. The result is presented in Fig.1b. Thus, as it is established that sigma scales with the critical current as expected from the Kurkijarvi theory, we look into the main result of the theory, namely that sigma~T^{2/3}Ic^{1/3}. From this it follows that the power of 2/3 should be recovered if sigma, normalized by the temperature-dependent critical current as sigma/Ic^{1/3}, is plotted versus T. This is indeed the case as is shown in Fig.1c. The power observed there is close to the expected 2/3. Some fluctuations of the power with the gate voltage remain unexplained.

ABSTRACTS

We investigate the stochastic nature of switching current of superconductor-graphene-superconductor (SGS) junctions with large critical currents, achieve by a â&#x20AC;&#x153;fingerâ&#x20AC;? geometry of the junction (Fig.1a). To make samples, graphene flakes are deposited on 280 nm thick SiO2 on the Si chip surface using mechanical exfoliation, using the Novoselov-Geim method. Raman spectroscopy is used to confirm the number of layers. The electrodes, which have a fingered shape (Fig. 1a), are patterned from a bilayer Pd/Pb (4nm/100nm).

References [1] U. C. Coskun, M. Brenner, T. Hymel, V. Vakaryuk, A. Levchenko, A. Bezryadin, Accepted for publication in Phys. Rev. Lett. (2012). [2] J. Kurkijarvi, Phys. Rev. B, 6, 832 (1972). [3] H. Meissner, Phys. Rev. Lett. 2, 458 (1959).

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Figure 1: (a) A scanning electron microscope (SEM) micrograph of a â&#x20AC;&#x153;finguredâ&#x20AC;? graphene junctions. Such design allows us to increase the critical current compared to straight junctions by a large factor. The electrodes (fingers) are made of Pd (4 nm) and Pb (100 nm). Lead is used as the material for the electrodes since it provides strong superconducting proximity effect [3] into graphene. The distance between the electrodes is about 300-400 nm. The accumulative length of the junctions varies from sample to sample and can be as long as 200 microns. Thus the fingered design allows us to obtain extra-long junctions. (b) Logarithm of the standard deviation of the switching current plotted versus the logarithm of the critical current. The scaling with the power of 0.34 is observed. This is in agreement with the Kurkijarvi theoretical prediction [2] that such power should be 0.333. (c) Normalized standard deviation plotted versus temperature. The power is about 0.6, which is close to the theoretically expected 2/3. Some fluctuations of the power with the gate voltage, which is the parameter for these curves, is not well understood currently.

Atomic-scale model for the contact resistance of a nickel-graphene interface

Anders Blom, Kurt Stokbro, Mads Engelund QuantumWise A/S, Lersø Parkallé 107, 2100 Copenhagen, Denmark anders.blom@quantumwise.com

A question of great importance for the possible use of graphene in integrated circuits is the magnitude of the contact resistance between graphene and metal electrodes, since a high contact resistance would limit the performance of field-effect transistors [1]. Several experimental studies have investigated the topic, but there is no clear consensus on the value or the dependence of the contact resistance on contact area, temperature and applied gate potential. There is therefore a need for complementary theoretical studies which can give insight about the physical mechanisms at play at the metal-graphene interface. Earlier first-principles calculations have focused on charge transfer between the metal and the graphene [2–5], but in this paper we aim to add new knowledge to the understanding of the graphene-metal contact by investigating the effect of covalent bond formation on the contact resistance. Graphene forms a strong covalent bond with nickel [2] which is similar to the bond formation between graphene and cobalt, palladium and titanium, thus, the theoretical predictions will also be relevant for these systems.

We will present quantum transport calculations of electron transfer from a free suspended graphene sheet to a nickel contact through different metal-graphene contact geometries, where we vary the orientation of the graphene and the contact area. We find that the contact resistance is independent of the orientation of the graphene, as well as of the contact area to the metal, in qualitative agreement with recent experimental observations [6]. Our calculations [7] show that indeed the low-field contact resistance is independent of the contact area, as well as of the direction of the graphene sheet. The edge contact resistance is about 30 Ωµm, corresponding to twice the ideal quantum contact resistance of pure graphene. We predict that this observation is generic for strongly bonded graphene, since we also see the same resistance when using a model contact between graphene and a hydrogen crystal or two overlapping graphene sheets.

ABSTRACTS

We suggest that our obtained contact resistance is the theoretical limit for an ideal bond between nickel and graphene. This value is still rather far from experimentally observed values, which indicates that the experiments do not deal with ideal contacts – impurities and defects are in all likelihood important factors to consider. But our calculations do suggest that, however formidable the problems in forming a good contact are, the challenge is still practical rather than fundamental.

References [1] [2] [3] [4] [5] [6] [7]

F. Xia, D. B. Farmer, Y.-M. Lin, and P. Avouris, Nano Lett., 10, 715 (2010). P. A. Khomyakov et al., Phys. Rev. B, 79, 195425 (2009). S. Barraza-Lopez et al., Phys. Rev. Lett., 104, 076807 (2010). J. Maassen, W. Ji, and H. Guo, Appl. Phys. Lett., 97, 142105 (2010). Q. Ran, M. Gao, X. Guan, Y. Wang, and Z. Yu, Appl. Phys. Lett., 94, 103511 (2009). K. Nagashio, T. Nishimura, K. Kita, and A. Toriumi, Appl. Phys. Lett., 97, 143514 (2010). The transport calculations where performed with Atomistix ToolKit, version 12.2, QuantumWise A/S (2012).

Figures

Figure 1: Top view (B-C plane) and side view (A-C plane) of one the systems investigated in this paper, viz. a zigzag edge graphene on top of a Ni(100) surface with 4 Ă&#x2026; binding overlap. The transport direction is along the C direction. The red curve shows the average electrostatic potential in the vacuum region.

ABSTRACTS

Figure 2: Transmission coefficient per transverse line segment at zero bias for the four different systems studied (the geometry of Fig. 1 is (a) here). Also shown is the transmission coefficient of an ideal graphene sheet.

Exfoliation and Sorting of Graphite flakes and inorganic two-dimensional materials

F. Bonaccorso , F. Torrisi , G. Privitera , V. Nicolosi , T. Hasan , G. Savini , N. Pugno and 1 A.C. Ferrari 1 2 3

Department of Engineering, University of Cambridge, JJ Thomson avenue, Cambridge CB3 0FA, UK School of Chemistry, School of Physics & CRANN Trinity College Dublin Dublin 2 Ireland Dept. of Structural Engineering, Corso Duca degli Abruzzi 24, 10129 Torino, Italy fb296@cam.ac.uk

Liquid-phase exfoliation of graphite [1] is a promising tool for mass production of single and multi-layer graphene flakes, as well as inks [2], thin films [1], and composites [3,4]. Here we report high yield production of graphene via low power sonication of graphite in sodium deoxycholate (SDC) followed by ultracentrifugation. There are two main approaches to ultracentrifugation: sedimentation-based separation (SBS) and isopycnic separation. The former discriminates particles by their difference in mass. The latter exploits density differences between particles in a density gradient medium [5,6]. Our results suggest that graphite exfoliation via sonication produces flakes with lateral sizes increasing with the number of layers. We thus exploit SBS to separate graphite flakes by number of layers [8]. TEM and Raman spectroscopy indicate that ~65% of the flakes produced by SBS are monolayer with average size ~600nm2 [9,10]. Isopycnic separation allows us to obtain larger flakes than SBS. This requires the creation of density differences between flakes with different number of layers. Surfactants provide this density variation [11]. In this case, sorting is strongly dependent on the surface/volume ratio and the coverage and clustering of the surfactant molecules. SDC is the most effective surfactant for exfoliation and sorting of graphite flakes, with ~60% of the flakes in the topmost fraction being monolayers, with average size 1Îźm2. Ultracentrifugation can also be used to sort nanodiamonds in terms of shape and dimensions, and can also be applied to inorganic layered materials, such as Boron Nitride, Tungsten Disulfide, Molybdenum Disulfide, etc.[12].

Y. Hernandez et al. Nature Nano, 3 (2008) 563. F. Torrisi, et al., arXiv:1111.4970v1 (2011). T. Hasan, et al., Adv. Mater. 21 (2009) 3874. T. Hasan, et al. Phys. Status Solidi B 247 (2010) 2953. M. S. Arnold et al., Nat. Nano 1 (2006) 60. F. Bonaccorso et al., Journal of Physical Chemistry C 114 (2010) 17267 R. W. Fox, A. T. McDonald, P. J. Pritchard, Introduction to Fluid Mechanic, Wiley, 6 Edition (2003) ISBN 0471202312 F. Bonaccorso et al. submitted (2012). O.M. Maragoâ&#x20AC;&#x2122; et al., ACS Nano, 4 (2010) 7515. F. Bonaccorso et al., Nature Photonics 4 (2010) 611. A. A. Green et al, Nano Lett. 9 (2009) 4031. J.N. Coleman et al. Science 331 (2011) 568.

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

ABSTRACTS

References

The atomic and electronic structure of well-defined graphene nanoribbons studied by scanning probe microscopy

M.P. Boneschanscher , J. vd Lit , Z. Sun , P. Liljeroth and D.Vanmaekelbergh a

Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands Department of Applied Physics, Aalto University School of Science, 00076 Aalto, Finland

m.p.boneschanscher@uu.nl

Despite the recent interest in graphene, there is still a lack of experimental studies on the electronic properties of atomically well defined graphene nanostructures. In order to have full control over the size, shape and edges of graphene nanostructures we use a chemical approach [1] to grow graphene nanoribbons (GNRs) on a gold (111) substrates. The GNRs have a fixed width and edge termination as determined by the choice of chemical precursor, resulting in armchair edges along the long axis of the ribbon and zigzag ends along the short axis. We studied the GNRs using scanning tunneling microscopy and spectroscopy as well as atomic force microscopy. We measured the atomic structure of individual GNRs and spatially resolved the local density of states at different energy values. We find that the electronic states of the GNRs close to the Dirac point are located at the zigzag ends of the nanoribbons, whereas the states far away from the Dirac point are located mostly along the armchair edges (figure 1). Comparison of our experimental results with density functional theory indicates that the states at the zigzag ends are spin polarized whereas the states along the armchair edge are spin degenerate. References [1]

J. Cai et al., Nature, 446 (2010) 470-473.

ABSTRACTS

Figures

Figure 1: Energy spectroscopy on a GNR (left). Mapping the local density of states shows that states around the Dirac point are localized on the zigzag ends of the ribbon, while states far away from the Dirac point are more localized along the armchair edges (right top). The model for the GNR indicating the armchair edges in blue and the zigzag ends in red shown together with an AFM image of the atomic backbone of one of the GNRs (right bottom).

Channeling of graphene in environmental TEM: towards zero-disorder nanolithography

Tim J. Booth, Filippo Pizzocchero, Marco Vanin, Henrik Andersen, Thomas W. Hansen, Jakob B. Wagner, Joerg R. Jinschek, Rafal E. Dunin-Borkowski, Ole Hansen and Peter Bøggild DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark tim.booth@nanotech.dtu.dk

Catalytic channeling of graphene by metallic nanoparticles is unique due to the tendency of the trenches to follow the graphene lattice orientations, and the possibility of forming long trenches in graphene with a width of a few nanometers, sub-nanometer edge roughness and consistent lattice orientation. We have studied the rich and complex microscopic behaviour of silver nanoparticle gasification in in-situ environmental transmission electron microscopy and account for some of the observed trends and phenomena, including the “shot-noise”-like discrete removal of carbon atoms from the graphene lattice resulting in Poisson distributed temperature dependent instantaneous measured particle velocities [1], and the fact that nearly all edges have zig-zag orientation. With the support of DFT calculations, we identify the rate limiting step to be the removal of carbon atoms from zig-zag edges. Other phenomena remain to be explained, such as the curious fact that the characteristic shape of even large silver particles appear to be determined by the 1D graphene-silver interface involving just a few hundred atoms. In the light of these findings, the scientific challenges and technological opportunities involved in turning this process into a zero-disorder nanolithographic technique are discussed.

References

ABSTRACTS

[1] Tim J. Booth, Filippo Pizzocchero, Henrik Andersen, Thomas W. Hansen, Jakob B. Wagner, Joerg R. Jinschek, Rafal E. Dunin-Borkowski, Ole Hansen and Peter Bøggild, Nano Letters 11 (2011) 2689 [2] Filippo Pizzocchero, manuscript in preparation.

Figures

Figure 1: TEM images of the transition between monolayer and bilayer etching (and vice versa) within a single channel. These footprints of the interface of the silver particles in the graphene are triangular in shape with <100> orientated edges, parallel to the zigzag direction of the graphene lattice. Highlighted angles in (b) 120o. Scale bars 5nm. c) A schematic representation of the catalytic etching process. (i) The oxygen molecules interact with the silver nanoparticles. (ii) After being adsorbed, the oxygen may dissociate. The atomic oxygen formed diffuses on the surface of the particle, possibly reaching the silver-graphene interface where it interacts with the carbon edge atoms. (iii) Carbon at the edge reacts with the oxygen at the interface and is gasified in the molecular form COx leaving a void which the catalyst particle moves to fill. (iv) Schematic representation of changes in the number of layers removed, c.f. (a,b) d-e) The triangular front of etching particles is clearly visible in these images. Scale bars 25 nm and 20 nm respectively.

ABSTRACTS

Figure 2: a) A three dimensional representation of the structure used in the DFT calculation. b-c) Schematic 2D projections of the structure shown in (a). In particular, in (b) the shape of the step is clear, while in (c) the position of the graphene flake with respect to the silver edge is exemplified. d-e) Scale representations in the ZY plane of the actual DFT relaxed graphene-silver interfaces for the armchair and zigzag edges respectively. In (d) two unit cells are shown, with one in (e).

Graphene technology for future mobile devices

Stefano Borini, Di Wei, Samiul Haque, Alan Colli, Piers Andrew, Jani Kivioja Nokia Research Center, 21 JJ Thomson Av., Cambridge,UK stefano.borini@nokia.com

Due to its various and outstanding peculiar properties, graphene is expected to provide a technological platform which will enable the development of new materials and applications. Therefore, radical advancements and innovations beyond state-of-the-art technologies can easily be envisaged, based on the strong driving force already demonstrated by graphene science in a plenty of R&D fields. Some main opportunities that could be provided by graphene technology for the development of future mobile devices will be presented, with special emphasis on the applications in energy harvesting and storage. Indeed, graphene represents an ideal material for the development of portable energy storage devices, thanks to the high specific surface area, the superior electrical conductivity, a high chemical tolerance and a broad electrochemical window. In addition, graphene is a â&#x20AC;&#x153;solution-processableâ&#x20AC;? material, thus allowing the preparation of colloid suspensions suitable for printing applications. Results on functionalized graphene inks [1] and on the realization of graphene-based flexible lithium batteries [2] (see fig.1) will be shown, demonstrating the potential of graphene technology in the field of energy storage. Moroever, graphene-based transparent electrodes for organic photovoltaic cells, together with the peculiar photo-thermoelectric effect observable in graphene p-n junctions, are likely to provide new opportunities in the realization of energy harvesting devices. Possible perspectives for mobile devices technology within such a field will be illustrated. Finally, a broader outlook on possible graphene-driven radical innovations in the development of future mobile devices will be given. References [1] D. Wei et al.,, Chem. Commun., 48 (2012) 1239. [2] D. Wei et al., J. Mater. Chem., 21 (2011) 9762.

Figure 1: Realization of a lithium battery based on graphene ink cathode and polymer electrolyte (from Ref.[2])

ABSTRACTS

Figures

Boron and nitrogen doping of graphene from first principles

Andrés R. Botello-Méndez, Bing Zheng, Xavier Declerck, Aurelién Lherbier, Luc Henrard and Jean-Cristophe Charlier Institute for condensed Matter and Nanosciences, Université catholique de Louvain, Chemin des étoiles 8, 1348 Louvain la neuve, Belgium andres.botell@uclouvain.be

The modification of the electronic properties of sp2 carbon nanostructures by the controlled addition of foreign atoms into the carbon lattice has been widely proposed and investigated [1,2], in close analogy to the doping of silicon in the semiconductors industry. However, in contrast with conventional materials, the effect of foreign atoms in nanostructures is expected to depend significantly on the position and surrounding of each atom due to the quantum confinement of the electrons [2]. In principle, the fact that nitrogen atoms contain one additional electron than carbon, suggests that nitrogen doped carbon nanostructures will exhibit the characteristics of an n-type material [3,4]. Similarly, boron atoms which lack of one electron with respect to carbon atoms are good elements to achieve a p-doped material [2]. Furthermore, recent experiments on graphene reveal through scanning tunneling microscopy (STM) images, that B and N doping can occur in different kinds of geometries [5,6]. This work explores different configurations for nitrogen and boron atoms incorporated onto graphene, and investigates their effects and properties using ab-initio electronic structure calculations. The computed total and local density of states reveal specific signatures for each type of defect, which could be correlated with experimental scanning tunneling spectroscopy (STS) measurements. In addition, STM images are presented in order to aid the eventual large scale identification of these defects. Our calculations, and recent experimental observations suggest that the classically assumed nitrogen incorporations into graphitic structures (i.e., single substitution and pyridinic), are not necessarily the most common. It is generally true, however, that substitution defects (single, double substitution) dopes graphene with electrons, and vacancy-nitrogen complexes (e.g. pyridinic, or single nitrogen + vacancy) add holes to the system. In contrast, boron atoms are usually found in substitution for carbon atoms in graphene. However, these are rarely observed isolated, but rather showing a tendency to form islands.

ABSTRACTS

In summary, we present an extensive study of the properties of different kinds of boron and nitrogen doping in graphene. We show that the structural details of the incorporated atoms can be extremely important for the electronic properties of the resulting doped material. In addition we show that specific fingerprints in STM and STS analysis can be obtained accurately from ab-initio calculations.

References [1] P. Ayala, R. Arenal, A. Loiseau, A. Rubio, and T. Pichler, Rev. Mod. Phys. 82 (2010), p. 1843. [2] M. Terrones, A. Filho, A. Rao. Doped Carbon Nanotubes: Synthesis, Characterization and Applications in Carbon Nanotubes Springer 2008, pp. 531-566. [3] P. Ayala, R. Arenal, M. RĂźmmeli, A. Rubio, and T. Pichler, Carbon, 48 (2010), pp. 575-586. [4] J-Y. Yi and J. Bernholc. Phys. Rev. B, 47 (1993), p. 1708. [5] L. Zhao, et al. Science, 333 (2011), pp. 999-1003. [6] D. Deng, et al. Chem. Mater., 23 (2011), pp. 1188â&#x20AC;&#x201C;1193.

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ABSTRACTS

Figure 1: Schematic image showing the different kinds of doping structures for both nitrogen and boron in graphene.

Field-effect tunneling transistor based on vertical graphene heterostructures

L. Britnell, R. V. Gorbachev, R. Jalil, B. D. Belle, F. Schedin, A. Mishchenko, T. Georgiou, M. I. Katsnelson, L. Eaves, S. V. Morozov, N. M. R. Peres, J. Leist, A. K. Geim, K. S. Novoselov, L. A. Ponomarenko School of Physics & Astronomy, University of Manchester, Manchester M13 9PL, UK liambritnell@gmail.com

An obstacle to the use of graphene as an alternative to silicon electronics has been the absence of an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state. We report a bipolar field-effect transistor that exploits the low density of states in graphene and its one atomic layer thickness. Our prototype devices are graphene heterostructures [1,2] with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room temperature switching ratios of ≈50 and ≈10,000 respectively. Such devices have potential for high frequency operation and large-scale integration. Our typical device vertical transistor architecture is as follows: we use graphene electrodes and a thin dielectric layer separating them in a vertical arrangement, with current flow perpendicular to the graphene’s basal plane, figure 1. The two graphene electrodes are etched into Hall bar geometry so that we can measure the transport properties of the graphene leads, figure 2. We are able to measure tunneling through the barrier—typically a few nanometers thick—by varying a bias voltage between the graphene electrodes. The application of a gate voltage dramatically alters the tunneling characteristics of the device, figure 3. We explain the changes in the tunneling characteristics in our devices by a simple model [1,3] comprising three effects. (i) Movement of the Fermi level in both graphene electrodes (ii) movement of the relative position of their electronic bands and also (iii) lowering the effective barrier height. These combined effects result in a large increase in the leakage current between the graphene electrodes. The best device we have fabricated using hBN has a modest on/off ratio of ~50 and our first MoS2 devices show a much improved ON/OFF ratio of ~104. These devices are promising in development of the much vaunted application of graphene logic circuits, allowing miniturisation and high speed operation as the expected transition time for carriers is expected to be on the order of femtoseconds [4].

ABSTRACTS

References [1] [2] [3] [4]

L. Britnell et. al., Science (2012) doi:10.1126/science.1218461 and Supporting material. P. A. Ponomarenko et. al., Nature Physics 7 (2011) 958–961. J. G. Simmons, J. App. Phys 34 (1963) 1793-1803. J. A. Simmons et al.,J. Appl. Phys. 84, (1998) 5626-5634

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ABSTRACTS

↑ Figure 1: Graphene field-effect tunneling transistor. (A) Schematic structure of our experimental devices. In the most basic version of the FET, only one graphene electrode (GrB) is essential and the outside electrode can be made from a metal. (B) The corresponding band structure with no gate voltage applied. (C) The same band structure for a finite gate voltage Vg and zero bias Vb. (D) Both Vg and Vb are finite. The cones illustrate graphene’s Dirac-like spectrum and, for simplicity, we consider the tunnel barrier for electrons. (E) An artistic schematic of our vertical transistor devices.

Figure 2: Graphene as a tunneling electrode. (A) Resistivities of the source and drain graphene layers as a function of Vg (B-D) Carrier concentrations in the two layers induced by gate voltage, which were calculated from the measured Hall resistivities. The shown device has a 4-layer hBN barrier.

Figure 3: Tunneling characteristics for a graphene-hBN device with 6±1 layers of hBN as the tunnel barrier. (A) I-Vs for different Vg (in 10 V steps). Note, that due to the finite doping, the minimum tunneling conductivity is achieved at Vg≈3V. The inset compares the experimental I-V at Vg=5V (red curve) with theory (dark) which takes into account the linear DoS in the two graphene layers and assumes no momentum conservation. Further examples of experimental curves and their fitting can be found in Supporting online material of reference (). (B) Zero-bias conductivity as a function of Vg. The symbols are experimental data, and the solid curve is our modeling.

Graphene synthesis using alcohol precursors

Jessica Campos Delgado, Andrés Botello-Méndez, Benoit Hackens, Thomas Pardoen, Jean-Christophe Charlier, Jean-Pierre Raskin Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium jessica.campos@uclouvain.be

Although the production of graphene through the mechanical exfoliation of graphite allowed the availability of graphene for fundamental studies, its applications where limited by the small flake sizes and low yield. Alternative routes to the production of graphene were imminent. The most popular alternative route saw the light in 2009 when the chemical vapor deposition (CVD) synthesis of graphene was reported using polycrystalline nickel as catalyst and methane as carbon source at low pressures [1-2]. Later that year the growth using commercial Cu foils was reported [3]. The synthesis technique relies on the decomposition of methane at ~1000°C at low pressure and its deposition on the metal catalysts. While on Ni the solubility of C is high, the growth mechanism is through the segregation and precipitation of carbon once the Ni is cooled down; in contrast, Cu has a low C solubility and the growth is mediated by surface adsorption [4]. Besides methane (CH4) other carbon precursors have been used in the synthesis of graphene. Reports of solid and liquid sources appear in the literature [5-6]. The above listed precursors are used in experiments at low pressure conditions (mTorr) and generally pure Ar and H2 or Ar-H2 mixtures are involved in the synthesis, which require a sophisticated set-up with pumping system, 2-3 gas lines available, flow meters, and proper piping for contents higher that 5% of H2 because of safety issues. Here we describe the synthesis of graphene via the thermal decomposition of alcohols at atmospheric pressure, using copper foils as catalyst and a single gas inlet consisting of a gas mixture of Ar-H2 with a safe concentration of H2 (5%).

ABSTRACTS

We have investigated the growth of graphene using two liquid precursors: 2-phenylethanol and ethanol. Commercial copper foils of 25 μm-thick have been purchased; after mild cleaning such foils are placed in the growth chamber set to temperatures of 950°C-980°C, the decomposition of the alcohols at this temperature leads to the growth of graphene on copper. We have studied the as-produced samples by means of scanning electron and optical microscopy. To perform further studies we transferred the samples to Si/SiO2 substrates using FeCl3 as copper etchant and PMMA as support/protection layer. The transferred films have been characterized using optical microscopy, Raman spectroscopy, and atomic force microscopy. In Figure 1A, we show a scanning electron microscopy image of a film of graphene on copper grown from ethanol. The typical wrinkles originating from the mismatch in thermal expansion coefficients of both materials are evident. Etching of copper and transference of the graphene film have been carried out. An optical image of a transferred film depicted in Figure 1B shows uniformity at a large scale.

In order to verify the sp2 nature and quality of the produced material we perform Raman spectroscopy measurements on the transferred films (Figure 1C). The high intensity of the 2D (Gâ&#x20AC;&#x2122;) band reveals the presence of monolayer graphene. In this work, we will expose in detail the synthesis and transfer procedures, our results obtained by several characterization techniques, and we will compare the quality of the synthesized materials depending on the alcohol used as precursor.

References [1] A. Reina, X. Jia, J. Ho, D. Nezich, H. Son, V. Bulovic, M.S. Dresselhaus, J. Kong. Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition. Nanoletters 9 (2009) 30-35. [2] K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, J.-H. Ahn, P. Kim, J.-Y. Choi, B.H. Hong. Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 457 (2009) 706-710. [3] 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, R.S. Ruoff. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science 324 (2009) 13121314. [4] X. Li, W. Cai, L. Colombo, R.S. Ruoff. Evolution of graphene growth on Ni and Cu by carbon isotope labeling. Nanoletters 9 (2009) 4268-4272. [5] Z. Sun, Z. Yan, J. Yao, E. Beitler, Y. Zhu, J.M. Tour. Growth of graphene from solid carbon sources. Nature 468 (2010) 549-552. [6] A. Guermoune, T. Chari, F. Popescu, S.S. Sabri, J. Guillemette, H.S. Skulason, T. Szkopek, M. Siaj. Chemical vapor deposition synthesis of graphene on copper with methanol, ethanol and propanol precursors. Carbon 49 (2011) 4204-4210.

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ABSTRACTS

Figure 1: Characterization of the produced graphene films. A) Scanning electron micrograph of the graphene film on copper right after synthesis. B) Optical microscopy image at 100x of the transferred graphene film (in light purple color) on a Si/SiO2 substrate, a crack at the left up corner leaves visible the substrate. Bluish traces correspond to PMMA residues. C) Raman spectroscopy spectra recorded at different spots of the transferred film.

Theory and hierarchical modeling of defective graphene, the effects of grain boundaries and oxidation

Johan Carlsson , Luca Ghiringhelli and Annalisa Fasolino

Accelrys Ltd, 334 Science Park, CB4 OWN Cambridge, UK Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands johan.carlsson@accelrys.com

ABSTRACTS

Graphene has extraordinary properties, but utilizing these properties in electronic applications requires the ability to grow large scale, defect-free graphene sheets. The ground breaking method to exfoliate graphene sheets from graphite crystals do provide defect-free graphene sheet over large length scales, but this method is not suitable for industrial scale production. Several other routes are currently pursued to synthesize graphene, such as annealing of SiC, CVD growth or oxidation of graphite, but the samples created in these ways are often found to be polycrystalline and may contain a variety of defects and functional groups. These defects in the as-grown polycrystalline graphene samples can, on the one hand, be detrimental for the properties of graphene, but on the other hand, offer a method to control its mechanical and electronic properties. However, the graphene research has up to now been focusing on perfect graphene and as-grown, defective graphene has only recently started to obtain some attention. Point defect in graphene may be generated by electron beam irradiation [1], but grain boundary engineering at the atomic level is still very challenging because no general theory is available, which is able to describe the various structures that have been observed in experiments. Scanning tunnelling microscopy (STM) investigations of a variety of [0001] tilt grain boundaries in graphene have shown that small angle grain boundaries have the shape of periodic arrays of asymmetric hillocks with large separation as demonstrated in Fig. 1a) [2], while a grain boundary with a misorientation angle q = 21째 could be characterized as a flat array of 5-7 ring complexes [3] and a grain boundary with a misorientation angle of 60째 had the shape of an array of 5 and 8 rings [4]. The shape and properties of the defects may be further tailored by controlled oxidation [5], as the basal plane of graphene is inert towards molecular oxygen and only vacancies are etched by O2 [6]. However, oxidation of graphene is a very complex process, where the individual steps are not yet completely understood. In order to improve the understanding of imperfect graphene, we have investigated the shape and effects of point defects and grain boundaries in graphene and how oxidation influence as-grown graphene. Our density-functional (DFT) calculations using the DMol-code showed that point defects in graphene form a complex of non-hexagonal rings in the hexagonal graphene lattice [7]. Further analysis revealed that these defects form semi-localized defect states, indicating that defects in graphene would have an increased chemical activity, which was later confirmed by our investigation of oxidation of graphene [8]. In addition, we have developed a general theory for the structure of [0001] tilt grain boundaries in graphene based on the coincidence site lattice (CSL)-theory [9]. The CSL-theory is convenient to derive supercell models for grain boundaries and we have implemented the method into a script in Materials Studio [10]. The script is able to generate grain boundary models for a particular misorientation angle q with two grain boundaries per supercell. The structure of a large set of the grain boundary models were geometry optimized by force field and bond order potential calculations and selected models were also optimized by DFT calculations using the CASTEP-code for reference. Our force field and DFT calculations show that low energy grain boundaries in graphene can be identified as dislocation arrays. Grain boundaries with small misorientation angles tend to form hillocks as shown in Fig. 1b). This occurs due to the strain at the dislocation cores in agreement with STM observations of small misorientation angle grain

boundaries in epitaxial grown graphene [2]. Our calculations have also shown that contrary to the usual bulk behaviour, in graphene there is an attractive interaction between dislocation cores that decreases the strain energy, so that the dislocation arrays form ridges for misorientation angles 10°<q <25° and flatten out for misorientation angles larger than q =25°. The structure of the grain boundary corresponding to the STM observation in [4] is then approximately a flat array of 5-7 dislocation core rings. The attractive interaction decreases the formation energy for grain boundaries with large misorientation angles so that a minimum occurs for S=13 at q =32.2°. Finally, we have investigated oxidation of graphene. Our DFT calculations using the CASTEP-code showed that dissociation of O2 of the basal plane of graphene is strongly endothermal, which provides an explanation to the inertness of defect-free graphene [8]. Further calculations for oxidation of vacancies indicated that low temperature etching of graphene proceeds through a two-step mechanism. Bare vacancies are very reactive towards O2 as our previous analysis indicated [7]. The O2 molecules get dissociated, such that the vacancies quickly get saturated by ether and carbonyl groups. These O-groups are stable with respect to CO-desorption below the critical temperature Tc, and they can be considered as the ground state in an oxygen atmosphere. The saturation of the bare vacancies is the first step in the oxidation reaction. The oxygen saturated vacancies are less reactive towards oxygen compared to the bare vacancies, but significantly more reactive than the basal plane. The oxygen molecules can be dissociated at the ether groups and this leads to the formation of larger O-groups, primarily lactones, which either desorb directly as CO2 or the lactones are further activated by additional O2 dissociation forming anhydride groups. The anhydride groups decompose rapidly and the CO2 desorption exposes new sites for O2dissociation, thus driving the etching reaction further. The dissociation of the oxygen molecules at the ether groups forming lactones and anhydrides is the second step in the oxidation process. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

A. Hashimoto, K. Suenaga, A. Gloter, K. Urita, and S. Iijima, Nature 430 (2004) 870. J. Coraux, A. T. N'Diaye, C. Busse, and T. Michely, Nano Lett. 8 (2008) 565. P. Simonis, C. Goffaux, P. A. Thiry, L. P. Biro, P. Lambin, and V. Meunier, Surf. Sci. 511 (2002) 319. J. Lahiri, Y. Lin, P. Bozkurt, I. I. Oleynik, and M. Batzhill, Nature Nanotech. 5 (2010) 326. A. Böttcher, M. Heil, N. Stürzl, S. S. Jester, S. Malik, F. Perez-Willard, P. Brenner, D. Gerthsen, and M. Kappes, Nanotech. 17 (2006) 5889. J. R. Hahn, Carbon 43 (2005) 1506. J. M. Carlsson and M. Scheffler, Phys. Rev. Lett. 96 (2006) 046806. J. M. Carlsson, F. Hanke, S. Linic and M. Scheffler, Phys. Rev. Lett. 102 (2009) 166104. J. M. Carlsson, L. M. Ghiringhelli, and A. Fasolino, Phys. Rev. B 88 (2011) 165423. Materials Studio release 5.5, Accelrys Software Inc., San Diego, USA (2010).

Figure 1: a). STM observation of the hillocks at a small angle grain boundary in graphene taken from [1]. b) Optimized structure of the atomistic grain boundary model having the same misorientation angle as the experiment. Taken from [4].

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Solution Processable Graphene and Other Two Dimensional Materials for Energy Applications

Manish Chhowalla Rutgers University, Department of Materials Science and Engineering, Piscataway, NJ 08854, USA Manish1@rci.rutgers.edu

ABSTRACTS

Chemical exfoliation of layered two-dimensional materials such as graphite and transition metal chalcogenides allow access to large quantities of atomically thin nanosheets that have properties that are distinctly different from their bulk counterparts. Although 2D materials have recently become popular, their fabrication via exfoliation of bulk crystals has been known for decades. For example, Brodie first exfoliated graphite into atomically thin oxidized form of graphene in 1859. In the case of layered transition metal dichalcogenides (LTMDs) such as MoS2, WS2, MoSe2, WSe2, etc., Frindt et al. performed seminal work in the â&#x20AC;&#x2DC;70s and â&#x20AC;&#x2DC;80s. We have revived these techniques to obtain a wide variety of chemically exfoliated two-dimensional nanosheets and utilized these materials in wide variety of electronic and energy applications. In this presentation, I will highlight some of our key contributions with graphene oxide (GO) and LTMD nanosheets. Specifically, I will present their implementation into large area electronics, strategic implementation into solar cells, and as catalysts.

Applications of Graphene-based Materials

Gary Economo and Gordon Chiu Grafoid Inc., 912-130 Albert Street, Ottawa, Canada gary@grafoid.com dr.chiu@grafoid.com

Chemistry, and the optimization of graphene processes when combined with the world’s best graphite feedstock are leading Grafoid towards a benchmark global standard for economically scalable, mass produced graphene. Hummer’s method resolves the scalability issue for graphene oxide but sacrifices quality. Growing graphene via chemical vapor deposition produces high quality graphene, but fails on economics. The challenge for scientists today is to produce pristine graphene for fifty cents per pound or less – down from its current cost of $20,000 per pound. Our research is leading us towards that goal. As applications in the scientific, medical, consumer, military and industrial sectors flourish and multiply, the need for a standardized, scalable process grows ever greater. As a wonder material, graphene’s role in energy storage - as the next anode material for lithium ion batteries to its role in ultra capacitors – is well known.

ABSTRACTS

Eliminating costs is the key to commercial success. Universal market acceptance by the investment community will come once mass producers of automobile, electronics and infrastructural components are assured of a sustainable, low-cost, viable graphene source.

Inducing magnetism in graphene in a view of spintronics

4,5

H. X. Yang , D. Terrade , D. W. Boukhvalov , X. Waintal , S. Roche and M. Chshiev 1

SPINTEC, CEA/CNRS/UJF-Grenoble, INAC, 17 rue des Martyrs, 38054 Grenoble, France Korea Institute for Advanced Study (KIAS), Hoegiro 87, Dongdaemun-Gu, Seoul 130-722, Korea CIN2 (ICN-CSIC) and Universitat Autonoma de Barcelona, Catalan Institute of Nanotechnology, Campus de la UAB, ES08193 Bellaterra (Barcelona), Spain 4 ICREA, Institucio Catalana de Recerca i Estudis Avancats, ES-08010 Barcelona, Spain 2 3

mair.chshiev@cea.fr

Graphene has emerged as one of the most promising material for developing "beyond CMOS" nanoelectronics [1]. It is very attractive for spin electronics (spintronics) [2] since long spin lifetimes are expected within this material due to its intrinsic weak spin-orbit coupling. Inducing magnetism in graphene, however, remains one of the most challenging problems for its applications to spintronics. Magnetic states in graphene can be induced using magnetic substrates, e.g. transition metals Co and Ni [3]. For instance, interesting perpendicular magnetic anisotropy properties of Co/graphene interfaces have been reported [4]. However, growing on conducting substrates limits graphene applications for electronic devices. Alternative possibilities are to use magnetic insulating material EuO as a substrate [5] or to explore shape induced magnetism in graphene nanomesh structures [6,7] inspired by recent reports on possibility of inducing localized spin polarization and magnetic moments at one-dimensional zigzag edges in graphene nanoribbons [8]. Here we present first principles investigations of both substrate and shape induced magnetism and report promising potential for producing high spin polarization and exchange splitting values [7].

ABSTRACTS

Our calculations were performed using Vienna Ab-Initio Simulation Package (VASP) which is based on density functional theory with generalized gradient approximation for exchange correlation and projector augmented wave based pseudopotentials [9]. All calculations have been performed to ensure the Hellman-Feynman forces acting on carbon atoms to be less than 10-3 eV/Å. First, magnetic properties in graphene nanomesh structures (GNM) will be presented. For pure GNM, nonspin-polarized states are found stable in armchair-type edges while antiferromagnetic states are found stable for balanced zigzag edge structures. Furthermore, an unbalanced edge structure shows stable ferrimagnetic state giving rise to a net magnetic moment up to 4 uB per 6 x 6 unit cell. We also found the gap opening in the balanced zigzag edge GNMs which may reach up to 0.40 eV. For hydrogen terminated GNM, we found that the ground state strongly depend both on the hole size and shape. For instance, a large net magnetic moment (~2.15µB and ~3.62µB) is induced in the ground state for GNM with pentagon and trianglular shaped holes shown in Fig. 1(h) and (c), respectively. At the same time, the ground state is found to be paramagnetic for GNM with rhombic and 6-ring shaped holes represented in Fig. 1(f) and (e). Interestingly, the net magnetic moment for GNM with intermediate between trianglular and rhombic shaped holes is equal to 1.04µB (Fig. 1(g)) providing that it scales between two end case values of 2.15µB and 0µB. The magnetization is found to depend strongly on GNM hole size as seen in Fig. 1 and 2. Such behavior can be explained in the framework of Lieb’s theorem with a few cases, however, going beyond the latter (Fig. 2(a)). Of note, magnetic configurations get more stable compared to non-magnetic ones as the hole sizes increases as seen in Fig. 2(b). Finally, one of the most interesting results is that the exchange

splitting increases as a function of ∆AB and reaches the values of the order of half eV (Fig. 2(a)) which is very promising for room temperature spintronics [7]. The second part of the presentation will be devoted to possibility of inducing spin polarization in graphene by means of magnetic insulator proximity effect. Using the optimized structure of graphene on EuO, we calculated the local density of states for this system. We found that due to very strong spin polarization of EuO substrate, magnetic properties of graphene are strongly affected. The average spin polarization in graphene layer is found to be about 12%. We will also discuss an impact of magnetic insulator proximity on Dirac point properties. This work was supported by Chair of Excellence Program of the Nanosciences Foundation in Grenoble, France, by French National Research Agency (ANR) Project NANOSIM_GRAPHENE, and by European Union funded STREP Project CONCEPT-GRAPHENE. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

A. K. Geim and K. S. Novoselov, Nature Materials, 6 (2007) 183 A. Fert et al, Mat. Sci. Eng. B, 84 (2001) 1; S. A. Wolf et al, Science, 294 (2001) 1488. A. Varykhalov et al, Phys. Rev. Lett., 101 (2008) 157601; O. Rader et al, Phys. Rev. Lett., 102 (2009) 057602. Chi Vo-Van et al, New J. Phys. 12, 103040 (2010) H. Haugen et al, Phys. Rev. B, 77 (2008) 115406. J. A. Furst et al, Phys. Rev. B, 80, 115117 (2009) H. X. Yang et al, Phys. Rev. B 84, 214404 (2011) Y.-W. Son et al, Nature, 444 (2006) 347; O. Yazyev et al, Phys. Rev. Lett., 100 (2008) 047209. G. Kresse and J. Hafner, Phys. Rev. B, 47 (1993) 558; P. E. Blöchl, Phys. Rev. B 50 (1994) 17953; G. Kresse and J. Joubert, ibid. 59 (1999) 1758.

Figure 2: (a) Total magnetic moment (μB /cell) (left) and spin-splitting (right) as a function of ∆AB for various GNM geometries. The result of the Lieb’s theorem prediction is also given for comparison. (b) Energy difference between ferrimagnetic and paramagnetic states.

Figure 1: (a)-(h) H-passivated GNMs with different shapes. The corresponding net magnetic moments for each structure are also indicated.

ABSTRACTS

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Graphene synthesized by Atmospheric Pressure Chemical Vapour Deposition

J.-F. Colomer and A.V. Tyurnina Research Center in Physics of Matter and Radiation (PMR), University of Namur (FUNDP), 61 rue de Bruxelles, B5000 Namur, Belgium jean-francois.colomer@fundp.ac.be

Our investigation is concentrated on the growth of graphene by atmospheric pressure chemical vapour deposition (APCVD) technique. This method is technologically more attractive for large scale production of graphene because it is inexpensive and readily accessible way for the growth of reasonably high quality graphene on the different metal substrates [1-3]. Most of the CVD growth methods use polycrystalline Ni or Cu films/foils, but Cu seems to be the best candidate for making large-area graphene films. Because of a low solubility of carbon in Cu (in comparison with Ni), the growth is restrained to the surface of the catalyst, thus allows the formation of single layer graphene (SLG) [3]. Under atmospheric pressure, methane and hydrogen gas mixtures at various ratios are used in the CVD process with a temperature ranged between 800-1000째C [3-4]. Mainly all of successful results were obtained for graphene deposited onto the Cu foils [5-6]. Another promising approach is to use metal films heteroepitaxially deposited on conventional single crystalline substrates as reported for the Co and Ni [7-8]. Using epitaxial Cu(111) deposited on c-plane sapphire, high quality SLG can be synthesized [9-10]. The proposed route of making graphene is based on the combination of plasma vapour deposition (PVD) and APCVD synthesis. The PVD technique is used to tailor the catalysts in order to allow the formation of uniform Cu films with required properties for graphene film grown on it. The APCVD technique implies the controlled synthesis of such film with fixed number of graphene layers. The effect of different parameters during the preparation of catalysts or/and the synthesis of graphene investigated using optical and electron microscopies (SEM and TEM), AFM, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy characterizations.

ABSTRACTS

Our studies are focused on adjusting APCVD for graphene growth on Cu catalysts. First of all sputtering route of catalyst preparation allows us to control the size and the shape of graphene films deposited on it. Additionally, this method allows the flexibility of transferring as-produced film to alternative substrates by wet-etching of the Cu catalysts. Based on our experience acquired in the past on the APCVD growth of carbon nanotubes, we tried to adjust CVD parameters for graphene formation. But actually, a key challenge for as-synthesized graphene concludes not only in finding the CVD conditions but also in tailoring the catalyst deposition. For the synthesis of graphene, catalyst deposition must be tuned to formation of uniform SLG film which should save continuity, flatness and homogeneity even after high temperature CVD process. To reach so, the best catalysts could be heteroepitaxial metal films.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Reina A. et al, Nano Lett. 9 (2009) 30. Kim, K. S. et al, Nature 457 (2009) 457, 706. Li, X., et al, Nano Lett. 9 (2009) 4268. Lee, Y., et al, Nano Lett. 10 (2010) 490. Yu, Q., et al, Nat. Mater. 10 (2011) 443. Vlassiouk, I., et al, ASC NANO 5 (2011) 6069. A. Ago et al, ACS NANO 4 (2010) 7407. T. Iwasaki et al, Nano Lett. 11 (2011) 79. K. M. Reddy et al, 98 (2011) 113117. B. Hu et al, 50 (2012) 57.

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Figure 2: Optical images of etching solution with graphene film supported by PMMA in it, transferred film onto the Si/SiO2 and Raman spectrum of as-transferred graphene.

ABSTRACTS

Figure 1: AFM image and Roughness, XRD pattern and hexagonal LEED pattern of epitaxial Cu(111) on sapphire.

Charge writing on graphene devices using low temperature scanning probe microscopy

1,2

E. D. Herbschleb , M. R. Connolly , R. K. Puddy , M. Roy , D. Logoteta , P. Marconcini , 1 1 4 3 1 J. Griffiths , G. A. C. Jones , M. Macucci , P. Maksym , C. G. Smith 1

Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK National Physical Laboratory, Hampton Road, Teddington TW11 0LW, UK Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK 4 Dipartimento di Ingegneria dell'Informazione, UniversitĂĄ di Pisa, Via G. Caruso 16, I-56122 Pisa, Italy 2 3

mrc61@cam.ac.uk

Electrostatic Erasable Lithography [1] (EEL) is a technique which uses the tip of an atomic force microscope to deposit charge above a two-dimensional electron system in order to define a quantum circuit. Graphene is an ideal platform for performing EEL owing to the exposure of its basal plane to charges in the environment. We recently demonstrated how EEL can be used to measure and modify the doping around metallic contacts in a graphene flake covered with a thin dielectric layer at room temperature [2,3]. Here we describe a technique that enables charge deposition to work at low temperature (4.2 K), thereby paving the way towards drawing circuits where quantum effects such as phase coherence begin to play a role. In contrast to charge writing at room temperature, we find that low temperature EEL requires the tip to be brought into direct contact with the dielectric, where charge can be written according to the tribocharging technique [4] (Figure 1). Subsequent imaging of the potential of the written charge using Kelvin probe microscopy [5] (KPM) enables us to extract the amplitude of the local surface potential, which can be over 10 V (Figure 1, insets). A systematic change in the bulk conductance of the contacted flake as a function of back-gate voltage (Figure 1, main) confirms that the deposited charge is strongly coupled to the underlying graphene. As a first step towards drawing quantum circuits in graphene, we fabricate a constriction comprising a positively charged dot in a negatively charged 400 nm-wide line. Scanning gate microscopy images [2] show a local response to the scanning tip at the locations where charge was written. Finally, we show how the charge may be erased by running a high current through the flake, thus enabling multiple quantum circuits to be designed and measured by EEL at low temperature.

ABSTRACTS

References [1] R. Crook, A.C. Graham, C.G. Smith, I. Farrer, H.E. Beere, and D.A. Ritchie, Nature 424 (2003), 751. [2] M.R. Connolly, K.L. Chiou, C.G. Smith, D. Anderson, G.A.C. Jones, A. Lombardo, A. Fasoli, and A.C. Ferrari, Appl. Phys. Lett. 96 (2010), 113501. [3] M.R. Connolly, E.D. Herbschleb, R.K. Puddy, M. Roy, D. Anderson, G.A.C. Jones, P. Maksym, C.G. Smith, arXiv:1111.0560v1 (2011). [4] A. Kleiner, O. Marti, U. DĂźrig, A. Knoll, B. Gotsmann, Journal of Applied Physics, 109 (2011), 124312. [5] M. Nonnenmacher, M.P. O'Boyle, and H.K. Wickramasinghe, Appl. Phys. Lett. 58 (1991), 2921.

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ABSTRACTS

Figure 1: [Top] Depiction of the scanning probe writing charge in a thin dielectric layer covering a contacted graphene flake. [Main] Conductance of the graphene device as a function of back-gate voltage after writing consecutively larger amounts of negative charge in a square region over the graphene. We quantify the amount of deposited charge by the average surface potential (VS), which is measured using Kelvin probe microscopy. Insets show maps of the surface potential obtained by Kelvin probe microscopy at VS = -0.5 V (left) and VS = -11.5 V (right). The position of the device is indicated by the overlaid lines.

Epitaxial graphene/metal hybrids

Johann Coraux Institut Néel – CNRS, France

A number of transition metals may serve a supports and catalysts for the growth of epitaxial graphene. In the last few years synthesis routes which were historically parallel are converging: on one hand, preparation under ultra-clean conditions, namely under ultra-high vacuum and at the surface of single crystal metals; on the other hand, growth under pressures approaching atmospheric conditions, at the surface of metallic thin films. In both cases graphene layers having high quality can be obtained. The first approach delivers model systems especially suited to fine surface science studies. The second approach is motivated by the prospect for mass production of graphene. I will present our recent studies on a particular graphene/metal system which is a case study for graphene weakly interacting on its substrate, graphene/Ir(111), which we have been revisiting since 2007 and allows for the preparation of ultra-high quality graphene [1-5]. I will show that even in such a high quality system, small small imperfections, causing distributions of the lattice parameter in graphene of a few hundredths of an ångström, are present [6]. I will then present our recent studies devoted to the deposit of metals on graphene/Ir(111), which leads to ordered two-dimensional arrays of magnetic nanoclusters [7] or ultrathin magnetic films intercalated between graphene and its metallic substrate [8]. References [1] [2] [3] [4] [5] [6] [7] [8]

J. Coraux et al. Nano Lett. 8, 565 (2008). J. Coraux et al., New J. Phys., 11, 023006 (2009). R. van Gastel et al., Appl. Phys. Lett. 95, 121901 (2009). H. Hattab et al., Appl. Phys. Lett. 98, 141903 (2011). C. Vo-Van, et al., Appl. Phys. Lett. 98, 181903 (2011). N. Blanc, et al., submitted. A. T. N'Diaye et al., New J. Phys. 11, 103045 (2009). C. Vo-Van et al., Appl. Phys. Lett. 99, 142504 (2011). J. Coraux, et al., submitted.

ABSTRACTS

Figures

Figure 1: A. Domains with varying local structure (left) and a domain wall with strain between two domains (right) (the hexagon's shape represent the shape of the graphene unit cell). B. Co clusters on graphene/Ir(111), which are intercalated between graphene and Ir upon annealing.

Quenching of the quantum Hall effect in graphene with scrolled edges

Alessandro Cresti , Michael M. Fogler , Francisco Guinea , A. H. Castro Neto and Stephan Roche 1

IMEP-LAHC (UMR 5130), Grenoble INP, Minatec, 3 Parvis Louis NĂŠel, F-38016 Grenoble, France Department of Physics, UC San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA 3 Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain 4 Graphene Research Centre, National University of Singapore, 2 Science Drive 3, 117542, Singapore 5 CIN2 (ICN-CSIC) and Universitat Autonoma de Barcelona, E-08193 Bellaterra, Spain 2

Compared to graphene deposited on substrate, suspended samples show exceptionally high charge mobility, which can even be orders of magnitude larger. Surprisingly enough, the integer quantum Hall effect is easily observable in deposited graphene even at room temperature, while its experimental demonstration for suspended samples has been difficult to achieve. The typical mechanism that causes the deviation from the integer quantum Hall effect is the crosslinking of the chiral channels due to strong disorder, as impurities [1] or elastic strains [2]. However, suspended graphene has very low disorder and the absence of substrate preserves it from remote Coulomb impurities. Moreover, the continuous progress of the experimental techniques has allowed the fabrication of samples with size up to several microns, for which such sources of scattering can be generally ruled out. Another factor that might play a role is that of hot spots [1] for samples in the four-terminal configuration, where the unfortunate placement of the contacts affects the potential felt by the probes, thus reducing of the Hall voltage. Again, the large size of the current samples makes this issue irrelevant in most cases. The only other known mechanism of disrupting the quantum Hall effect is edge reconstruction, which can generate counter-propagating channels at the same edge. However, previously discussed edge reconstructions [3,4] are not unique to suspended graphene and originate from a generic tendency of a 2D metal to have an irregular density near the edge. In this contribution, we propose an alternative explanation for the difficult observation of the quantum Hall effect in suspended graphene. Our analysis starts from the matter-of-fact that suspended graphene often has scrolled edges, as commonly observed experimentally [5]. In general, scrolling is most common in four-terminal devices as the graphene samples are suspended underneath the contacts and these regions are loose and can easily scroll. In the region of the scrolls, the component of the magnetic field perpendicular to the graphene surface oscillates and changes its sign due the curvature. This translates into an effective almost vanishing magnetic field nearby the edge regions, and it turns the scrolls into conventional non-chiral conductors, where backscattering can be easily induced by a minimum amount of disorder. The current in these regions flows in parallel with the current in the flat part of the sample, thus leading to the quenching of the quantum Hall effect. We support this scenario by simulating electronic structure and transport in large graphene nanoribbons with scrolled edges under magnetic fields up to 20 T [6], fig.1. From the calculation of the energy bands, fig.2, we clearly demonstrate the rise of non-chiral edge states, with the typical Dirac-like dispersion, which coexist with the usual Landau states in the bulk region. The simulations of electronic transport based on the Green function formalism, figs.3 and 4, show the detrimental impact that disorder has on the transmission of the non-chiral channels and, consequently, on the global conductance quantization. Note that strain is not supposed to play any role, because either it is absent (scrolls form to release strain) or it is so inhomogeneous that the effect of the generated pseudomagnetic fields vanishes.

ABSTRACTS

crestial@minatec.inpg.fr

Our results provide a consistent and meaningful interpretation of the possible suppression of quantum Hall regime in suspended graphene and rationalize its complicate observation. References [1] [2] [3] [4] [5] [6]

I. Skachko, X. Du, F. Duerr, A. Luican, D.A. Abanin et al., Phil. Trans. Roy. Soc. A, 368 (2010) 5403. E. Prada, P. San-Jose, G. Léon, M.M. Fogler, and F. Guinea, Phys. Rev. B, 81 (2010) 161402(R). A.H. Castro Neto, F. Guinea and N.M.R. Peres, Phys. Rev. B, 73 (2006) 205408. P.G. Silvestrov and K.B. Efetov, Phys. Rev. B, 77 (2008) 155436. J.C. Meyer, A.K. Geim, M.I. Katsnelson, K.S. Novoselov, T.J. Booth et al., Nature, 446 (2007) 60. A. Cresti, M.M. Fogler, F. Guinea, A.H. Castro Neto and S. Roche, arXiv:1111.4437v1.

Figures

Figure 1: Configuration of the system under study in which a suspended graphene ribbon has scrolled edges. The ribbon is attached to the source and drain contacts. The arrows indicate the external current.

Figure 2: Band structure of a scroll with the inner and outer radii and ro=11.1 nm, ri=9.91 respectively, at B=20T computed from the Dirac equation with the zigzag edge boundary condition. The dashed lines are defined by equations E=~v(kx ± lB −2 ro), where v is the velocity of electrons at the charge neutrality point of 2D graphene, lB is the magnetic length and kx is the component of the wave vector along the scroll axis. The cross-section of the system is sketched in the bottom right corner of the figure. For clarity, the flat region (full width 100 nm) is truncated and the layer separation inside the scroll is enlarged.

ABSTRACTS

Figure 3: (a) Band structure of a flat 100 nm wide armchair nanoribbon under a perpendicular magnetic field B=20T. (b) Conductance as a function of the electron energy for pristine and disordered ribbons. Disorder extends over a section of length 210 nm and includes a short-range component generated by randomly varying the on-site energies within the range [−25,25] meV, and a ﬁnite-range component given by 50 Gaussians impurities with range ξ=1 nm and strengths in the range [−500,500] meV. Thanks to the chirality of the edge channels, the integer quantum Hall eﬀect is robust against disorder and the conductance quantization is observed. (c) Corresponding shot-noise, which indicates the perfect transmission except around the van Hove singularities.

Figure 4: (a) Band structure of a100 nm wide armchair nanoribbon under a perpendicular magnetic field B=20T in the presence of nanoscrolls of arc length 15 nm and two full turns. (b) Conductance as a function of the electron energy for pristine (black dashed lines) and disordered (blue solid lines).The quantization is clearly destroyed in the whole energy spectrum, with the exception of the region of the first plateau, where non-chiral channels are absent. (c) Corresponding shot-noise, which confirms the strong enhancement of backscattering.

Applications for Graphene films: market trends

J. de la Fuente Graphenea, San Sebastian, Spain

During the past two years, advances in Graphene CVD synthesis and transfer have opened new research and industrial applications to the landscape. Outstanding properties of Graphene films, homogeneity, industrial-scalability and reproducibility are the main drivers for the development of new Graphene films based devices. Most applications to date have been focused in the Energy Storage applications mainly in batteries and ultracapacitors. Using Graphene films to enhanced electrodes has yield in an exceptional performance improvement for these devices. Graphene enhanced Solar cells are also an intensive research topic. The other group of leading applications is related to Electronics and Semiconductors mainly in the High Frequency Electronics applications. In some cases, proof of concepts and prototypes has been developed. Transparent conductors, Biosensors and Advanced Composites complete the list of leading innovations using Graphene films.

ABSTRACTS

In order to evolve to the next step to develop early stage technology products some key success factors have to be considered. The key success factors to move forward in the development of the Graphene films industry will be presented and discussed.

Flexible GHz Transistors Derived from Solution-Based Single-Layer Graphene

Cédric Sire , Florence Ardiaca , Sylvie Lepilliet , Jung-Woo T. Seo , Mark C. Hersam , 2 2 1 Gilles Dambrine , Henri Happy and Vincent Derycke 1

CEA Saclay, IRAMIS, Service de Physique de l’Etat Condensé, Laboratoire d’Electronique Moléculaire, F-91191 Gif sur Yvette, France 2 Institut d’Electronique, de Microélectronique et de Nanotechnologie, UMR-CNRS 8520, BP 60069, Avenue Poincaré, F-59652 Villeneuve d’Ascq, France 3 Department of Materials Science and Engineering and Department of Chemistry, Northwestern University, Evanston 60208-3108, Illinois, USA vincent.derycke@cea.fr

The potential of graphene transistors for high frequency electronics was recently demonstrated by several groups using exfoliated, SiC-based and CVD-based graphene. The most recent studies reached deembedded current gain cut-off frequencies (fT) in the 100-300 GHz range with room for improvement at both the material and device levels. In parallel, graphene is being explored for large scale electronics on flexible substrates via CVD growth on metal foils associated with transfer methods. This progress is driven by the perspective of replacing ITO as the material of choice for the transparent electrodes required in applications such as touch screens, flat panel displays or organic photovoltaic cells. However, the combination of these two properties, namely high speed and flexibility, remains an open challenge. In particular for the viable development of fast and flexible electronic applications in the areas of portable / wearable communicating devices with low power consumption, this combination should be achieved with a source of material adapted to low-cost manufacturing methods such as ink-jet printing.

ABSTRACTS

Printed electronics based on organic materials is a well established field. Organic materials are particularly well suited for flexible circuits due to their mechanical resiliency. Yet, their low charge mobility limits their ultimate operating frequency. While several examples of organic devices and circuits operating in the kHz to MHz range have been demonstrated, these approaches fall well short of the GHz range. Conversely, inorganic semiconducting materials such as III-V semiconductor nanowires and silicon thin films can reach the GHz range, but few studies have evaluated their performances upon severe bending and these inorganic materials are not ideally adapted for future printed technologies. Carbon-based nanomaterials potentially combine high speed performance with the required mechanical properties. In particular, carbon nanotubes were used to develop high frequency transistors on rigid substrates and to demonstrate flexible devices and circuits. Recently, graphene transistors on flexible substrates were realized, but their high frequency performance was not evaluated. In this work [1], we demonstrate that solution-based single-layer graphene ideally combines the required properties and presents important advantages over alternative graphene sources that are chemically grown or mechanically exfoliated. Several methods of producing stable graphene-based suspensions have been recently demonstrated. In particular, there have been extensive efforts to utilize graphene oxide as a solution-phase precursor for graphene. However, this approach requires subsequent chemical reduction treatments that preclude complete recovery of the superior electrical properties of pristine graphene. Alternatively, exfoliation of graphite is also possible. While this procedure is effective at isolating few-layer pristine graphene, polydispersity in the thickness of graphene produced from these processes implies inferior performance compared to single-layer graphene in high-performance electronic applications. To overcome these issues, we employ solution-based, predominantly single-layer graphene flakes isolated via

density gradient ultracentrifugation [2] to fabricate flexible transistors on organic substrates operating at GHz frequencies. The devices operate at low bias (VDS<0.7 V), achieve current gain cut-off frequencies fT as high as 2.2 GHz before de-embedding (8.7 GHz after de-embedding), power gain cut-off frequency fMAX of 550 MHz and have a constant transconductance in the GHz range [1]. In addition, we show that both the electron and hole conduction branches display high-speed performance, in contrast with previous reports where only one type of carrier was considered due to the either high n-type or p-type doping of the graphene used. RF measurements directly performed on bent samples show the remarkable mechanical stability of these devices and demonstrate the advantages of solution-based graphene FETs over other types of flexible transistors based on organic materials. References [1] C. Sire, F. Ardiaca, S. Lepilliet, J-W. T. Seo, M.C. Hersam, G. Dambrine, H. Happy, V. Derycke, Nano Lett. (2012) in press (DOI: 10.1021/nl203316r). [2] Green, A. A.; Hersam, M. C. Nano Lett. 9 (2009) 4031-4036.

Figures

ABSTRACTS

Figure 1: (a) Evolution of the current gain H21 measured at 510 MHz as a function of the gate bias of an as-prepared graphene-FET on polyimide. (b) Evolution of the transconductance as a function of frequency showing stable performances up to ~5 GHz (VGS=-1V for holes and 1V for electrons). (c) Picture of a series of flexible graphene FETs on polyimide. (d) Evolution of the current gain H21 (before and after de-embedding) and of the power gain U for a p-type device after Joule annealing. The as-measured cut-off frequency fT is 2.2 GHz.

Photo-thermo- vs. photo-electric effects in metal-graphene-metal photodetectors 1

T.J. Echtermeyer , P.S. Nene , M. Trushin , R.V. Gorbachev , A.L. Eiden , S. Milana , Z. Sun , J. 2 4 5 1 Schliemann , E. Lidorikis , K.S. Novoselov and A. C. Ferrari 1

Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany 3 Centre for Mesoscience & Nanotechnology, University of Manchester, Oxford Road, Manchester, M13 9PL, UK 4 Department of Materials Science and Engineering, University of Ioannina, Ioannina, Greece 5 School of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom 2

Tje29@cam.ac.uk

The electrical and optical properties of graphene make it an ideal material for photonics and optoelectronics [1]. Graphene based photodetectors with a bandwidth up to 16 GHz have been demonstrated and integrated into an optical communication link operating at 10 Gbit/s [2], proving their suitability for high-speed photodetection over a wide wavelength range. However, the underlying physical mechanism is still under debate as both photo-thermoelectric [3,4,5] and photoelectric effects [6,7,8] are being suggested. We carry out wavelength and polarization dependent photovoltage mapping of metalgraphene-metal junctions, demonstrating that both effects simultaneously contribute to the photoresponse. These measurements allow us to quantify the wavelength dependent ratio of thermo- vs. photoelectric effects from the visible to the near-infrared. Fig. 1 shows the optical micrograph of a typical metal-graphene-metal photodetector. Gold contacts are prepared to contact exfoliated single-layer graphene by means of e-beam lithography, metal evaporation and a lift-off step. Subsequently, photovoltage-mapping is carried out by scanning linearly polarized laser light with diffraction limited spot size over the sample and recording the position dependent photoresponse of the device. By varying the incident laser light wavelength and polarization, information about the contributing mechanisms to the overall photoresponse can be acquired. Fig. 2 shows the photovoltage in dependence of the polarization angle ÎŚ with respect to the metal contact long edge (0 deg denoting perpendicular to the edge). It can be observed that the photovoltage follows a cos2(ÎŚ) dependence. This behavior can be explained by considering the pseudospin selection rule for anisotropic generation of electron-hole pairs in the driving term of the Boltzmann equation which is a clear proof for a photo-electric effect in graphene-based photodetectors. Further, the ratio of the oscillating vs. nonoscillating part of the photovoltage allows an estimation of the ratio of photo-thermalvs photo-electric effects.

ABSTRACTS

References [1] [2] [3] [4] [5] [6] [7] [8]

F. Bonaccorso, Z. Sun, T. Hasan, A.C. Ferrari, Nat. Photonics 4, 611 (2010). T. Mueller, F. Xia, P. Avouris, Nat. Photonics 4, 297 (2010). X. D. Xu et. al. , Nano. Lett. 10, 562 (2010). M.C. Lemme et. al. , Nano Lett. 11, 4134 (2011). N.M. Gabor et. al. , Science 4, 648 (2011). E. J. H. Lee et. al. , Nat. Nanotechnol. 3, 486 (2008). T. Mueller, F. Xia, M. Freitag, J. Tsang, Ph. Avouris, Phys. Rev. B 79, 245430 (2009). S. Mai, S. V. Syzranov, K. B. Efetov, Phys. Rev. B 83, 033402 (2011).

Figures

Figure 1: Optical micrograph of a metal-graphene-metal photodetector.

ABSTRACTS

Figure 2: Normalized photovoltage in dependence of the incident laser light polarization angle for different wavelengths.

Magnetic and electronic structures of nanographene and fluorinated nanographene with an interplay of edge-state spins and dangling bond spins

Toshiaki Enoki Department of Chemistry, Tokyo Institute of Technology, W4-1/2-12-1, Meguro-ku, Tokyo 152-8551 Japan enoki.t.aa@m.titech.ac.jp

The magnetic structure of graphene is modified drastically by introducing edges and defects. Here, localized non-bonding edge states of π-electron origin having localized spins are created when a graphene sheet is cut along the zigzag direction, while defects, which are not terminated, have magnetic σ-dangling bond states. We investigated the magnetic and electronic properties of nanographene with a focus of interplay between the edge-state spins and dangling bond spins, using nanoporous activated carbon fibers (ACFs), which are a 3D disordered network of nanographene sheets, and their fluorinated derivatives, by means of NEXAFS, ESR and magnetic susceptibility. NEXAFS experiments indicate the presence of edge state (peak position 284.5 eV) around the Fermi level in nanographene together with the π*-conduction band (peak position 285.5 eV). The large negative chemical shift (-1.0 eV) of the NEXAFS peak from the peak of the π*-conduction band is suggested to be a consequence of large screening effect, which is associated with a large local density of states of the edge state of nonbonding π–electron. ESR result proves that the edge state is magnetic with localized spin. A nanographene sheet, whose periphery is described in terms of a combination of zigzag edges and armchair edges, is found to have ferrimagnetic structure with a net nonzero magnetic moment as a result of cooperation of strong intra-zigzag-edge ferromagnetic interaction and intermediate strength interzigzag-edge ferromagnetic/antiferromagnetic interaction. Heat-treatment of the ACFs induces an insulator-to-metal (IM) transition around 1200 ˚C. This strengthens inter-nanographene exchange interaction in the 3D nanographene network, bringing about a spin glass state in the vicinity of the IM transition. Fluorination of ACFs proceeds in two step manner; fluorination of the edge carbon atoms first and then that of the carbon atoms in the interior [Figure 1]. The first step taking place up to F/C~0.4 works to decrease the magnetic edge-state contribution due to the local destruction of the zigzag edges as evidenced by a monotonical decrease in the spin concentration, while magnetic σ-dangling bond states are created at the carbon site adjacent to the carbon atom attacked by a fluorine atom in the interior of a nanographene sheet in the second step that takes place above F/C~0.4 after all the edge carbon atoms are terminated with fluorine atoms. The spin concentration of the dangling bonds starts increasing above F/C~0.4, it is maximized when a half of the interior carbon atoms (F/C~0.8) are bonded with fluorine atoms and finally it becomes negligible at a saturated fluorine concentration of F/C~1.2. This scenario of the fluorination process, which is suggested by the magnetic measurement, is confirmed by the NEXAFS. NEXAFS shows an extra peak assigned to the dangling bonds in the fluorinated ACFs at 284.9 eV above F/C~0.4. The small negative shift of -.0.6 eV of the peak is a consequence of weak screening effect of the σ-dangling bond states having a small local density of states. The NEXAFS intensity of the σ-dangling bond states tracks the behavior of the concentration of the σ-dangling bond spins with fidelity. A combination of magnetic susceptibility, ESR and NEXAFS experiments demonstrates that the edge-state spins have itinerant nature with a fractional magnetic moment whereas the dangling bond spins are localized in nature with a magnetic moment of 1 μB and are free from exchange interaction.

ABSTRACTS

References [1] M. Kiguchi, V. L. J. Joly, K. Takai, T. Enoki, R. Sumii, K. Amemiya, Phys. Rev. B84 (2011) 045421. [2] T. Enoki, Proc. Nobel Symposium on Graphene and Quantum Matter, Physica Scripta T, 146, 014008 (2012).

Figures

ABSTRACTS

Figure 1: Schematic model of the fluorinated ACFs at (a) F/C<0.4 and (b) F/C=0.4~0.8. The edge carbon atoms bonded to two neighboring carbon atoms are terminated by two fluorine atoms (large circles). A -dangling bond (ellipsoids with a dot inside) is created at a carbon site bonded to the carbon atom attacked by a fluorine atom in the interior of a nanographene sheet. (c) The intensities of the π-edge state (squares), π-dangling bond state (circles), and π* state (triangles) peaks as a function of fluorine concentration, obtained NEXAFS experiments. (d) The total localized spin concentration (squares) as a function of fluorine concentration. The expected total density of magnetic moments in the FACF (stars) obtained by multivariable analysis of the NEXAFS spectra with the contributions of the edge state and σdangling bond state.

The Graphene Science and Technology Roadmap

Vladimir Falko , Andrea C. Ferrari , Francesco Bonaccorso, Kostya S. Novoselov 1 2

School of Physics and Chemistry Lancaster University LA1 4YB, Lancaster, UK Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge, CB3 0FA, UK

ABSTRACTS

We will present the â&#x20AC;&#x153;The Graphene Science and Technology Roadmapâ&#x20AC;? produced by the Graphene Flagship pilot action in conjunction with the national communities of the EU member states. We will outline the way this roadmap was conceived, its main objectives, together with its most salient features in terms of research and applications. This will include a brief overview of grand challenges in topics such as high frequency electronics, flexible displays, photonics, optoelectronics and plasmonics, as well as composites, inks, production and up-scaling.

Dynamic RKKY interaction in grapheme

M. S. Ferreira School of Physics, Trinity College Dublin, Dublin 2, Ireland

ABSTRACTS

The growing interest in carbon-based spintronics has stimulated a number of recent theoretical studies on the RKKY interaction in graphene, based on which the energetically favourable alignment between magnetic moments embedded in this material can be calculated. The general consensus is that the strength of the RKKY interaction in graphene decays as 1/D3 or faster, where D is the separation between magnetic moments. Such an unusually fast decay for a 2-dimensional system suggests that the RKKY interaction may be too short ranged to be experimentally observed in graphene. Here we show in a mathematically transparent form that a far more long ranged interaction arises when the magnetic moments are taken out of their equilibrium positions and set in motion. We not only show that this dynamic version of the RKKY interaction in graphene decays far more slowly but also propose how it can be observed with currently available experimental methods.

Graphene and spintronics

2,3

A. Fert , A. Anane , C. Berger , W. de Heer , C. Deranlot , B. Dlubak , L. Hueso , H. Jaffrès , 1 5 1 1 2 6 6 1 M-B. Martin , N. Mathur , F. Petroff , P. Seneor , M. Sprinkle , B. Servet , S. Xavier , H. Yang . 1

Unité Mixte de Physique CNRS/Thales, Palaiseau and Université Paris-Sud, Orsay, France School of Physics, Georgia Institute of Technology, Atlanta, USA 3 Institut Néel, CNRS, Grenoble, France 4 CIC Nanogune, San Sebastian, Spain 5 Department of Materials Science, University of Cambridge, Cambridge, UK 6 Thales Research and Technology, Palaiseau, France 2

albert.fert@thalesgroup.com

Several spintronic devices (logic gates, spin FET, etc) are based on spin transport in a lateral channel between spin polarized contacts. We will present, with experiments in support, an overall picture of the properties of carbon nanotubes and graphene for the transport of spin currents to long distance in such types of device. Their advantage over classical semiconductors and metals comes from the combination of their large electron velocity with their long spin life time due to the small spin-orbit coupling of carbon. This leads to spin diffusion lengths ≈ 100 μm. For graphene, the experiments we present are magneto-transport measurements on graphene multilayers on SiC [1] connected to cobalt electrodes through alumina tunnel barriers. In terms of ΔR =ΔV/I, the spin signals, at low and room temperature, are in the MΩ range, well above the spin resistance of the graphene channel. The analysis of the results in the frame of drift/diffusion equations [2] leads to spin diffusion length in graphene around 100 mm for a series of samples having different lengths and different tunnel resistances . The advantage of the graphene is not only the long spin diffusion length. The large electron velocity also leads to short enough dwell times even for spin injection though tunnel barriers. Our results on graphene can be compared with previous results [3] obtained by some of the authors (L.H., N.M., A. F.) on carbon nanotubes with also spin signals ΔR in the MΩ range (ΔR/R up to 72%) and spin diffusion lengths around 50 μm. A unified picture of spin transport in nanotubes and graphene will be presented. In conclusion, carbon-based conductors like carbon nanotubes and graphene, with their combination of a long spin life time with a large electron velocity and the resulting long spin diffusion length, turns out as materials of choice for large scale logic circuits and the transport/processing of spin information. Understanding the mechanism of the spin relaxation, improving the spin diffusion length and also testing various concepts of spin gate are the next challenges.

ABSTRACTS

References [1] W.A. de Heer, C. Berger, X. Wu, M. Sprinkle, Y. Hu, M. Ruan, J.A. Stroscio, P.N. First, R. Haddon, B. Piot, C. Faugeras, M. Potemski, and J.-S. Moon, Journal of Physics D: Applied Physics, 43, 374007, 2010. [2] H. Jaffrès, J.-M. George, and A. Fert, Physical Review B, 82, 140408(R), 2010. [3] L.E. Hueso, J.M. Pruneda, V. Ferrari, G. Burnell, J.P. Valdes-Herrera, B.D. Simons, P.B. Littlewood, E. Artacho, A. Fert, and N.D. Mathur, Nature, 445, 410, 2007.

Performance assessment of graphene-based devices through a multi-scale approach

G. Fiori, G. Iannaccone Dipartimento Ingegneria dell’Informazione, Università di Pisa, Via Caruso 16, 56122, Pisa, Italy gfiori@mercurio.iet.unipi.it

Evaluating the potential performance of graphene-based devices is an issue suitable to be addressed by numerical simulations. In order to be predictive, such simulations have to deal with quantum effects involved at the atomistic level. Due to the reduced geometry, implemented physical models have to go beyond the effective mass approximation widely exploited in the past: the flexibility of atomistic approaches is indeed required to explore issues at this dimensional scale. In this work, we will shed a light on the ultimate performance to be expected from devices at the end of the ITRS roadmap, in which graphene is exploited as channel material. To this purpose, we will present our method of choice for the simulation of graphene devices, i.e. a multi-scale approach, based on an atomistic investigation of the material properties through ab-initio simulations, which will feed tightbinding simulations, thus allowing to provide accurate results, but with reduced computational requirements with respect to Density Functional Theory simulations. In order to get a clear understanding of the physical behaviour of realistic devices, transport equations have to be solved self-consistently with the Poisson equation. A versatile tool for this task is NanoTCAD ViDES [1], the first software package for the simulation of graphene devices released under an opensource license, capable to self-consistently solve the 2D and 3D Poisson equation together with the Schroedinger equation with open boundary conditions, within the Non-Equilibrium Green’s Function (NEGF) formalism [2]. By exploiting the code we can investigate the performance on a wide set of devices, ranging from 1D dimensional transistors (based on nanotubes [3], graphene nanoribbons [4], one-dimensional heterojunctions [5]) to 2D dimensional transistors (based on monolayer and bilayer graphene [6-8], and on heterojunctions between graphene and other two-dimensional materials [9]). In particular, attention will be focused on the evaluation of the main figures of merit for digital applications, such as the largest achievable current in the on state (Ion) as well as the smallest current when the device is switched off (Ioff), and the ratio (Ion/Ioff). For applications in analog electronics, we will focus on voltage gain and on cut-off frequency as a function of different device structures.

url: http://www.nanohub.org.tools/vides. DOI:10254/nanohub-r5116.5. (DOI: 10254/nanohub-r5116.5). S. Datta, Superlattice and Microstructures, Vol. 5, 523, 2000. G. Fiori, G. Iannaccone, G. Klimeck, IEEE Transaction on Electron Devices, Vol. 53, pp. 1782-1788, 2006. G. Fiori, G. Iannaccone, IEEE, Electron Device Letters, Vol. 28, Issue 8, pp. 760 - 762, 2007. L. Leem, A. Srivastava, S. Li, B. Magyari-Kope, G. Iannaccone, J. S. Harris, G. Fiori, IEDM 2010, p. 740. G. Fiori, G. Iannaccone, IEEE Electron Device Letters, Vol. 30, pp.1096-1098, 2009. G. Fiori, G. Iannaccone, IEEE Electron Device Letters, Vol. 30, pp. 261-264, 2009. B. N. Szafranek, G. Fiori, D. Schall, D. Neumaier, H. Kurz, Nano Letters, to be published ASAP. G. Fiori, A. Betti, S. Bruzzone, G. Iannaccone, ACS Nano, to be published ASAP.

[1] [2] [3] [4] [5] [6] [7] [8] [9]

ABSTRACTS

References

Figures

Figure 1: Graphene nanoribbon FET device

ABSTRACTS

Figure2: Tunnel FET bilayer graphene FET.

Tuning the transport properties of graphene through AC fields

3,4

Luis E. F. Foa Torres , H. L. Calvo , L. H. Ingaramo , H. M. Pastawski , S. Roche 1

Instituto de Física Enrique Gaviola (IFEG)–CONICET, FaMAF, Universidad Nacional de Córdoba; Instituto de Física Enrique Gaviola (IFEG)–CONICET, FaMAF, Universidad Nacional de Córdoba 2 Institut für Theorie der Statistischen Physik, RWTH Aachen University, D-52056 Aachen, Germany 3 CIN2 (ICN–CSIC), Catalan Institute of Nanotechnology, Universidad Autónoma de Barcelona, Campus UAB, 08193 Bellaterra (Barcelona), Spain 4 Institució Catalana de Recerca i Estudis Avançats (ICREA), 08070 Barcelona, Spain lfoa@famaf.unc.edu.ar

More than a century ago, the use of alternating currents (ac) sparked a revolution that changed our modern world. Today, the use of ac fields has reached the nanoscale. Here, the interplay between the quantum coherence of the electrons, inelastic effects and dynamical symmetry breaking offers fascinating opportunities for basic research and applications. The interest on time-dependent excitations by electromagnetic fields or gate voltages has been steadily growing [1] and many captivating phenomena such as photon-assisted tunneling, coherent destruction of tunneling [2] and quantum charge pumping [3] have been unveiled. Graphene and carbon nanotubes offer an outstanding ground for these studies [4,5,6]. Here we give a brief overview of our recent research on driven electronic transport in these materials with a twofold focus: the effects of radiation on electronic transport properties in graphene [6], notably the emergence of dynamical band gaps, and how defects in carbon-based devices could help to generate a dc current in the presence of ac fields [7]. More specifically, we will try to shed light on questions such as: Is it possible to use ac fields to control the electric response (current and noise)? Could we achieve tunable band gaps in graphene through illumination with a laser of suitable wavelength and polarization (see Fig. 1 and its caption)? What is the role of defects in quantum pumping through carbon-based devices? A brief overview of other facets of the wealth of phenomena that could be awaiting us, such as the possibility of using the laser fields to generate the so called Floquet Topological Insulators [8,9,10], will also be presented.

[1] S. Kohler, J. Lehmann, and P. Hänggi, Phys. Rep. 406 (2005) 379 . [2] F. Grossmann, T. Dittrich, P. Jung, and P. Hänggi, Phys. Rev. Lett. 67 (1991) 516. [3] M. D. Blumenthal et al., Nature Physics 3 (2007) 343; B. Kaestner et al., Phys. Rev. B 77 (2008) 153301; B. Kaestner et al., Appl. Phys. Lett. 94 (2009) 012106; F. Giazotto et al. Nature Physics 7 (2011) 857. [4] L. E. F. Foa Torres, G. Cuniberti, Appl. Phys. Lett. 94 (2009) 222103; C. G. Rocha, L. E. F. Foa Torres and G. Cuniberti Phys. Rev. B 81 (2010) 115435. [5] L. E. F. Foa Torres, H. L. Calvo, C. G. Rocha, G. Cuniberti, Appl. Phys. Lett. 99 (2011) 092102. [6] H. L. Calvo, H. M. Pastawski, S. Roche, and L. E. F. Foa Torres, Appl. Phys. Lett. 98 (2011) 232103. [7] L. Ingaramo and L. E. F. Foa Torres, to be published. [8] N. H. Lindner, G. Refael, and V. Galitski, Nature Physics, 7, 490 (2011); T. Kitagawa, E. Berg, M. Rudner, and E. Demler, Phys. Rev. B 82 (2010) 235114. [9] T. Kitagawa, T. Oka, A. Brataas, L. Fu, and E. Demler, Phys. Rev. B 84 (2011) 235108. [10] Z. Gu, H. A. Fertig, D. P. Arovas, and A. Auerbach, Phys. Rev. Lett. 107 (2011) 216601; B. Dóra, J. Cayssol, F. Simon, and R. Moessner, Phys. Rev. Lett. 108 (2012) 056602.

ABSTRACTS

References

Figures

Figure 1: (Left) Scheme of the proposed setup where a laser field is applied perpendicular to a graphene monolayer. (Right) Effective density of states (DOS) as a function of the incident electron energy for three different laser polarizations: linear (a), elliptic (b) and circular (c). The DOS for unirradiated graphene (gray line) suffers dramatic modifications when the laser beam with ħΩ=140meV is turned on (the solid black and red dotted curves are for intensities of 32 mW/mm2 and 130 mW/μm2 respectively). As a result of the interaction between the electrons and the radiation, dynamical gaps open at ± ħΩ/2 and even at the Dirac point for circularly polarized light. These results are taken from Ref. [6], where we showed the first atomistic simulations of the electrical response (dc conductance) of a large graphene ribbon. Our results hint that a transport experiment carried out while illuminating with a laser in the midinfrared could unveil these phenomena.

ABSTRACTS

A full list of related publications is available at http://nanocarbon.famaf.unc.edu.ar/

Bloch-Zener oscillations as a probe of Dirac points merging in artificial graphene

Jean-Noël Fuchs, Lih-King Lim and Gilles Montambaux Laboratoire de Physique des Solides, Université Paris Sud, 91405 Orsay, France jean-noel.fuchs@u-psud.fr

By varying band parameters, Dirac points can be manipulated and merged at a topological transition towards a gapped phase. For example, Dirac points in graphene can be manipulated by applying stress to the crystal. However the topological merging transition is unreachable as it would require unphysically large deformations of the graphene sheet. Recently, an experiment conducted in ETH Zürich realized a kind of “artificial graphene” by loading ultracold fermions in a tunable brick-wall optical lattice [1]. Under a constant force, a Fermi sea initially in the lower band can perform Bloch oscillations and may Zener tunnel to the upper band mostly at the location of the Dirac points. Bloch oscillations and Landau-Zener tunneling were used in this experiment to detect the presence/absence of Dirac points as a function of optical lattice parameters. A vanishing tunneling probability was interpreted as a disappearance of Dirac points due to a merging transition. We propose a simple anisotropic square tight-binding hamiltonian as a minimal model to describe such an experiment [2]. At low energy it maps onto a so called universal hamiltonian [3] describing the vicinity of the merging transition. We compute the corresponding tunneling probability and obtained a very good agreement with the experiment. In addition, we study Stückelberg oscillations in such a system and show how they could be observed in a strictly 2D gas. We also discuss the merging point, at which a semi-Dirac spectrum (linear in one direction, quadratic in the other) is expected and should lead to new physics.

References

ABSTRACTS

[1] L. Tarruell, D. Greif, T. Uehlinger, G. Jotzu and T. Esslinger, arXiv:1111.5020 (to appear in Nature 2012). [2] L.-K. Lim, J.-N. Fuchs and G. Montambaux, arXiv:1201.1479 (to appear in Phys. Rev. Lett. 2012). [3] G. Montambaux, F. Piéchon, J.-N. Fuchs and M.O. Goerbig, Phys. Rev. B 80, 153412 (2009) and Eur. Phys. J. B 72, 509 (2009).

Broadband Photodetection with Graphene Devices

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1,3

Michael S. Fuhrer , Jun Yan , Xinghan Cai , Myoung-Hwan Kim , Jennifer A. Elle , Andrei 1,2 1,2 1,3 1,2 B. Sushkov , Greg S. Jenkins , Howard M. Milchberg and H. Dennis Drew 1

Department of Physics Center for Nanophysics and Advanced Materials Institute for Research in Electronics and Applied Physics University of Maryland, College Park, MD 20742-4111, USA 2 3

mfuhrer@umd.edu

Grapheneâ&#x20AC;&#x2122;s unique massless, gapless bandstructure gives rise to strong, broadband interactions with light. We report on two different broadband (THz to visible) photodetectors using graphene. The first photodetector exploits the gate-tunable bandgap of bilayer graphene to produce a temperaturedependent resistivity, allowing bolometric detection at temperatures of 5-20 K of visible (1.88 eV), near infrared (1.2 eV), and mid-infrared (0.12 eV) radiation, and/or electrical joule heating[1]. The large heat resistance between electrons and phonons in graphene due to the weak electron-acoustic phonon interaction is directly measured. A near infrared (1.2eV) excitation pump-probe study verifies the intrinsic electron-acoustic phonon energy relaxation time on order 1 ns which promises device operation to gigahertz frequencies. Optimized graphene hot electron bolometers could compare favorably to traditional silicon bolometers and superconducting transition edge detectors in noise equivalent power, speed, and sensitivity. The second photodetector extends the known photovoltaic effect at graphenemetal junctions to the THz regime by coupling an appropriate antenna structure to graphene through dissimilar metal electrodes which allow rectification of the THz signal to produce a dc photocurrent[2]. Detection of 3 THz radiation at room temperature is demonstrated, and the possibility of plasmonenhanced detection will be discussed.

References

ABSTRACTS

[1] J. Yan, M.-H. Kim, J.A. Elle, A.B. Sushkov, G.S. Jenkins, H.M. Milchberg, M.S. Fuhrer, and H.D. Drew, arXiv:1111.1202. [2] X.H. Cai, A.B. Sushkov, G.S. Jenkins, M.S. Fuhrer, and H.D. Drew, in preparation.

Graphene field effect transistors for bioelectronic applications

Lucas Hess, Max Seifert, Markus Dankerl, Benno Blaschke, Eric Parzinger, Christoph BeckerFreyseng, Martin Stutzmann, Jose A. Garrido Walter Schottky Institut, Technische Universität München, Am Coulombwall 4, Garching, Germany garrido@wsi.tum.de

The development of the future generation of neuroprosthetic devices will require the advancement of novel solid-state sensors with a further improvement in the signal detection capability, a superior stability in biological environments, and a more suitable compatibility with living tissue. Due to the maturity of Si technology, Si-based MOSFETs have been extensively used in previous decades for these applications. However, several disadvantages of Si technology, such as a relatively high electronic noise and poor stability in aqueous environment have motivated the search for more suitable materials. In this respect, the outstanding electronic and electrochemical performance of graphene holds great potential for bioelectronic applications. In this contribution, we will discuss our work towards the development of a graphene-based platform for applications in bioelectronics. In particular, we will report on graphene solution-gated field effect transistors (G-SGFETs) which can detect the electrical activity of electrogenic cells. Arrays of SGFETs were fabricated using CVD-grown graphene, grown on Cu and transferred to insulating substrates. Typically, 4x4 transistor arrays with dimensions of the device’s active area of 20x10 µm2 were processed and encapsulated for in-electrolyte characterization (Fig 1a). The electronic properties of these devices were investigated by Hall effect experiments performed under electrolyte-gate controlled conditions. The obtained mobility-carrier density curves (Fig 1b) are typical for high quality CVD graphene, with a carrier mobility limited by surface polar phonon scattering introduced by the polar sapphire substrate. The carrier mobility reaches values up to 104 cm2/Vs, in the low carrier density regime.

The biocompatibility of CVD graphene has been study using cultures of pure retinal ganglion cells (RGCs). Our results confirm that graphene exhibit similar behavior than other biocompatible materials such as glass. In addition, it will be shown how the growth of RGCs neurites can be directed by graphene patterning. Further, we will report on the recording of the electrical activity of different cell lines using arrays of graphene solution-gated field effect transistors (Fig 2a). Action potentials induced in dense cultures of cardiomyocytes-like HL-1 cells are spatially and time-resolved by the graphene SGFETs (Fig 2b) [3]. The electrical coupling between a single cell and a graphene SGFET was studied by using HEK cells in a patch-clamp configuration. Without the need of signal averaging, single recordings reveal not only the electrical but also the chemical activity at the cell/transistor interface (Fig 2c). These results demonstrate the potential of graphene to outperform state-of-the-art Si-based devices for biosensor and bioelectronic applications.

ABSTRACTS

Graphene SGFETs (Fig 1c) are compared to state-of-the-art Si-SGFETs based on the sensitivity and lowfrequency noise performance of these devices [1]. The high carrier mobility in graphene, together with the large interfacial capacitance at the graphene/electrolyte interface, leads to transconductive sensitivities one order of magnitude higher than for Si devices [2]. Furthermore, G-SGFETs exhibit very low electronic noise, with an RMS value that is equivalent to gate signals of less than 8 µV [3].

Finally, we will discuss how the facile integration of graphene with flexible substrates, together with the excellent signal-to-noise ratio of graphene FETs and their sensitivity to the electrolyte composition hold great potential in the field of electrically functional neural prostheses [4]. Acknowledgments This work is partially supported by the German Research Foundation under the priority program GRAPHENE, the Nanosystems Initiative Munich (NIM), and the EU under the FP7 program (project NEUROCARE).

References [1] [2] [3] [4]

Danker et al., Adv. Funct. Mater., 20 (2010) 3117 Hess et al., Appl. Phys. Lett., 99 (2011) 033503 Hess et al., Adv. Mater., 23 (2011) 5045 Work in progress under the FP7-EU project NEUROCARE

Figures

ABSTRACTS

Figure 1: a. Graphene transistor array on sapphire. b. Hall-effect carrier mobility versus carrier density for CVD grown graphene structures measured using an electrolyte gate. c. Typical transistor curves measured in electrolyte with a 2 Ag/AgCl reference electrode. Transistor dimensions are 20x10 Âľm .

Figure 2: a. Human embryonic kidney (HEK) cells cultured on a graphene transistor. b. Recordings of the transistor array in a culture of cardiomyocyte-like cells, revealing the spontaneously elicited action potentials and noise levels below 30 ÂľV. c. HEK cell on a transistor gate region stimulated with a pipette electrode. The transistor recording (light blue=single recording, dark blue=averaged signal) nicely follows the stimulation current signal (red curve).

Preparation routes to aqueous graphene dispersions and their influence on electrical conductivity of polymer composites

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Marcos Ghislandi , Evgeniy Tkalya , Alexander Alekseev , Cor Koning and 1 Gijsbertus de With 1

Laboratory of Materials and Interface Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands 2 Laboratory of Polymer Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands 3 Dutch Polymer Institute DPI, PO Box 902, 5600 AX Eindhoven, The Netherlands m.g.ghislandi@tue.nl

The chemical synthesis of graphene using graphite, graphite oxide (GO) or other graphite derivatives as starting materials have been extensively studied. The conversion of graphite into GO via Hummers or similar methods is an initial stage for different approaches. The water soluble GO can be reduced with the use of chemicals1, or quickly thermally expanded2 to form graphene. Recently, the long-term (e.g. more than 200 h) simple mechanical exfoliation (sonication) of graphite dispersed in polar solvents, as well as in water/surfactant systems, were reported as methods that yield single and multilayer graphene platelets at relatively high concentrations3. The chosen conversion techniques not only can be up-scaled but also can provide graphene with improved processability and potentially new functionality. The exfoliated dispersions are most suitable for the preparation of polymer composites with enhanced mechanical and electrical properties. In this work, starting from graphite, we produced graphene dispersed in water following the two main chemical conversion approaches (Oxi/Red Chemically and Oxi/Red Thermally) and a physical conversion via ultrasonic exfoliation (Sonic Solution). Subsequently, graphene /polystyrene (PS) composites were prepared using the well-known latex technology. The latex concept enables the incorporation and proper dispersion of nanofillers into any kind of highly viscous polymer such as PS, e.g. synthesized by emulsion polymerization or similar processes4. A comparison of the three chosen techniques with respect to filler morphology and conductive properties of the respective nanocomposites is presented.

The conductivities of the graphene/PS nanocomposites, obtained by both four point and local current measurement techniques, reveal high values up to 15 S/m and a low percolation threshold

AFM showed that the GO reduction techniques yield thin graphene platelets, and as a consequence also induce wrinkling/agglomeration and possible size reduction of the platelets, especially for the Oxi/red Thermally samples. Nevertheless, the thickness of the majority of the sheets measured is between 1 and 3 nm, corresponding to a single or only a few layers of graphene. For the Sonic Solution graphene samples analyzed, the thickness measured was higher (5 to 25 nm) and the average size was smaller, indicating multi-layer graphene. As the samples are much thicker, no wrinkling was observed.

ABSTRACTS

Water/surfactant solutions were prepared with the nanofillers prepared via the three methods described above and latex technology was applied for the preparation of conductive graphene/polystyrene composites, with well-dispersed graphene platelets. Each dispersion was mixed with PS latex, frozen in liquid nitrogen for several minutes, and subsequently freeze dried. The resulting composite powders were heated up and then compression molded into films. The samples were characterized (Raman, UV-Vis, AFM, SEM) with respect to filler properties and morphology, and their influences on electrical conductive properties of the composites were compared.

(0.9 wt.%) for the Oxi/red Chemically composites (Fig. 1). SEM and Conductive-AFM (see Fig. 2) show the different graphene shapes, even inside the polymer, depending on the filler production method used. Interesting differences in electronic transport behavior were also noticed, indicating at first glance direct contact transport for Oxi/red Chemically graphene in contrast with tunneling for Oxi/red Thermally and Sonic Solution graphene. The conductive properties of the composites studied mainly depend on the initial morphological characteristics of the produced graphene and its posterior organization inside the polymer matrix. These characteristics may have an important influence also on the electronic transport behavior through the composite.

References [1] S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. T. Nguyen, R. S. Ruoff, Carbon 2007, 45, (7), 1558-1565. [2] M. J. McAllister, J. L. Li, D. H. Adamson, H. C. Schniepp, A. A. Abdala, J. Liu, M. Herrera-Alonso, D. L. Milius, R. Car, R. K. Prud'homme, I. A. Aksay, Chemistry of Materials 2007, 19, (18), 4396-4404. [3] M. Lotya, P. J. King, U. Khan, S. De, J. N. Coleman, Acs Nano 2010, 4, (6), 3155-3162. [4] E. Tkalya, M. Ghislandi, A. Alekseev, C. Koning, J. Loos, Journal of Materials Chemistry 2010, 20, (15), 3035-3039.

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Figure 1: Volume electrical conductivity of graphene/PS composites as a function of graphene weight fraction. Values represent an average of 10 measurements for each sample; standard deviations are below 10%.

Figure 2: C-AFM of the composites cross secrtion areas for the three graphene used. A) Oxi/red Chemically (inset linear I-V curve), B) Oxi/red Thermally and C) Sonic Solution (inset exponential-like I-V curve) composites. Green/red spots correspond to graphene paths wich contributes to conductivity through the sample.

Graphene based electronics and electron ‘optics’: quantum transport and device opportunities

Redwan Sajjad, Frank Tseng and Dincer Unluer and Avik W. Ghosh Electrical Engineering, University of Virginia, Charlottesville, VA 22901, USA

Electronic conduction in graphitic materials can be quantitatively understood quite readily using the Landauer transmission theory. We will start by showing that a wide variety of experiments can be explained (Fig. 1) simply in terms of an integral over the mode spectra determined by the density of states, along with an energy-dependent scattering length dictated by Fermi’s Golden Rule [1]. The theory, however, needs to be supplemented with a more involved atomistic model when the sheets are narrowed down to nano-ribbon sizes [2]. Using non-orthogonal Extended Huckel Theory, we demonstrate that the edges of narrow armchair nanoribbons resemble benzene minus their resonant stabilization chemistry, imposing thus a molecular property to graphene electronics. The resulting strain along the edges removes any signatures of metallicity, while edge roughness filters out the chiral segments with smaller bandgaps, making the channel width the single arbiter of metallicity. We can thus design wide-narrow-wide all graphene devices monolithically patterned out of a single graphene template [3]. A full solution of Poisson’s equation coupled with quantum transport using a fully atomistic non-equilibrium Green’s function (NEGF) formalism shows that such a structure benefits from the dual advantages of a superior 2D contact electrostatics as well as a quasi-Ohmic carbon based contact resistance, mitigating short-channel effects that plague modern day silicon devices. However, the bane of these devices, predictably, is their narrow bandgaps that lead to band-to-band tunnelling, once again, consistent with multiple experiments. Our atomistic models allow us to quantify these effects [4]. The electronic gateability of graphene is fundamentally compromised by a trade-off imposed by an asymptotic property of its bandstructure [5]. Atomistic simulations show that on opening a bandgap by various techniques (specifically, selective doping of sheets, quantization in nanoribbons, and the use of transverse fields in Bernally stacked bilayer sheets), the bandstructure stays pinned to a linear dispersion at high energies, so that the bandgap opens not by a simple translation, but by an actual distortion of the bands. Such a distortion fundamentally increases the effective mass all throughout the band, quantifiable in simple terms, leading to a reduction of their mobility even in the absence of any increase in scattering rate. We predict a ~1/Eg reduction the mobility coming from the increase in effective mass alone, and a further ~1/Eg reduction from an increase in scattering length (for bilayer sheets, there is, in addition, a sweet spot due to Van Hove singularities, but the overall trend is still a fundamental reduction in mobility with increasing band-gap). This means that with increase in switching reliability (ie, ON-OFF ratio), there is an invariable reduction in switching speed (ON current), which limits the design space for graphene based electronic switches. Extended to graphene based inverters, we expect accordingly a reduction in gain, a reduced voltage swing and a poor saturation of the transfer characteristics, in close quantitative agreement with experiments [6]. A question we raise at the end is whether it is at all possible to design a graphene based switch without structurally distorting it in the process of opening a band-gap. We show that this is in principle possible using purely geometrical means, exploiting the pseudospin structure of the phase-coupled graphitic conduction and valence bands. It is, in fact, this property that fundamentally distinguishes graphene from other 2D semiconductors such as silicon inversion layers, boron nitride or molybdenum disulfide. In all narrow-bandgap semiconductors, a low voltage band-to-band tunneling causes electrons to follow trajectories reminiscent of Snell’s law in optics, albeit with a ‘refractive index’ that can be gate tuned into negativity. However, it is the pseudospin structure that determines the strength and angular quenching of the refracted and reflected waves (the equivalent of Fresnel coefficients in optics) – in other words, Klein-antiKlein tunneling in regular or bilayer sheets. In fact, we can see how this pseudospin rotates as we incrementally open a bandgap and thereby introduce a pseudo-magnetic field. Our results compare well with recent experiments that show how this pseudospin selectivity controls a graphene pn junction resistance (both on exfoliated and CVD grown samples), with varying tilt angles. The theoretical and experimental gateability of a Klein tunnel switch is still quite modest to be of interest from a device switching perspective. What we argue is that by introducing an additional scattering barrier from a non-graphitic structure (e.g. a cut in a graphene sheet), we can introduce a transmission gap that arises when the angle subtended by the cut at the source exceeds the critical angle for the graphene electrons. Aside from introducing a large ON-OFF ratio,

ABSTRACTS

ag7rq@virginia.edu

the significant development is that this gap can be collapsed by reducing the voltage gradient across the junction [7]. Such a gate tunable metal insulator transition does two things – it eliminates the current on the heterogeneous PN side of the voltage axis [8], and significantly sharpens the rising current on the homogeneous PP or NN side, in fact, exceeding the thermodynamic limit imposed by Boltzmann statistics that limits present day silicon based transistors. The unipolar, subthermal switch (Fig. 1) arises simply because we can tune the transmission gap of the heterostructure with a gate voltage, a property once again, unique to graphene and its pseudospin structure. We show how it allows us to design a high quality inverter that can operate at a higher frequency [9]. We also show how the ability to control the electron trajectory helps create reconfigurable electronic devices based on graphene heterojunctions. The gate tunability of the gap is supported by fully atomistic simulations of current flow through large (~200x600nm) sheets. However, these simulations also emphasize how sensitive graphene based electron ‘optics’ tends to be, outlining three significant challenges that need to be overcome – (i) we need ways to collimate the electrons without significantly excising their modal density and reducing the ON currents; (ii) we need ways to create high quality sheets and patterned contacts to avoid unintentional rotations of the pseudospins from pseudo-magnetic fields at these junctions; and (iii) most significantly, we need ways to flush out the electrons at the edges, which otherwise tend to redirect the electrons back towards the junctions and create large, dissipative leakage paths.

References [1] "Graphene Nanoribbons: from chemistry to circuits", F. Tseng, D. Unluer, M. R. Stan and A. W. Ghosh, invited book chapter (Graphene Nanoelectronics: Metrology, Synthesis, Properties and Applications", Ed. H. Raza, Springer Series in Materials Science 2012). [2] "Diluted chirality dependence in edge rough graphene nanoribbon field-effect transistors", F. Tseng, D. Unluer, K. Holcomb, M. Stan and A. W. Ghosh, Appl. Phys. Lett. Vol. 94, 223112 (2009). [3] "Monolithically Patterned Wide-Narrow-Wide All-Graphene Devices", Dincer Unluer, Frank Tseng, Avik W. Ghosh, Mircea R. Stan, IEEE Trans. Nano. issue 99, 2010. [4] "Graphene Devices, Interconnect and Circuits -- Challenges and Opportunities", Mircea R. Stan, Dincer Unluer, Avik Ghosh and Frank Tseng, IEEE International Symposium on Circuits and Systems (ISCAS), pp 69-72, 2009. [5] "From low-bias mobility to high-bias current saturation: fundamental trade-offs in graphene based transistors", Frank Tseng, Avik W. Ghosh, cond-mat/arXiv:1003.4551 [6] Frank Tseng, Dincer Unluer , Hong-yan Chen, Jeorg Appenzeller and Avik W. Ghosh, unpublished. [7] "High efficiency switching using graphene based electron optics", R. Sajjad and A. W. Ghosh, Appl. Phys. Lett. Vol. 99, 123101 (2011) [8] “Unipolar current voltage characteristics with graphene pn junctions”, R. Sajjad and A. W. Ghosh, in preparation. [9] Redwan Sajjad, Chen-Yun Pan, Azad Naeemi and Avik W. Ghosh, unpublished.

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Figures

Figure 1: (Left) Experiments and (center) theory [1] showing graphene I-Vs with contact induced asymmetry and band-toband tunneling. (Right) atomistic simulations show that across a graphene heterojunction with a split gate, electronic transmission can be quenched by the geometrical property of the pseudospin states (top) and completely eliminated with a regular (as opposed to Klein) tunnel barrier in the graphene structure, using a cut for instance [9].

Study of double dip in the transfer characteristics of graphene based field-effect transistors

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Filippo Giubileo , Antonio Di Bartolomeo , Salvatore Santandrea , Francesco Romeo , 1,2 3 3 Roberta Citro , Thomas Schroeder and Grzegorz Lupina 1

CNR-SPIN Salerno, via Ponte don Melillo, 84084 Fisciano (SA), Italy Dipartimento di Fisica E. R. Caianiello and Centro Interdipartimentale Nanomates, UniversitĂ degli Studi di Salerno, via Ponte don Melillo, 84084 Fisciano (SA), Italy 3 IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany giubileo@sa.infn.it 2

We present measurements on Cr/Au-contacted long-channel (~10 Âľm) graphene transistors on Si/SiO2 substrate. We report the observation of hysteresis as well as double dips in the transfer characteristics, that, as far as we know, have never been reported before on GFET with Cr/Au electrodes. Charge trapped in the surrounding dielectric and in particular in silanol groups at the SiO2 surface is at the origin of hysteresis; on the other hand, the gradient of carrier along the channel caused by electron transfer from the graphene to the Au/Cr contacts and the band shift induced by the back-gate voltage and the SiO2trapped charge are proposed to accounts for the double-dip feature. We show that p-n junctions are spontaneously formed by charge transfer between graphene and electrodes, and a double Dirac point can be achieved when low-resistivity contacts are fabricated. We further clarify the role of charge stored at the SiO2 interface in the formation of the double dip. Theoretical modeling of experimental data was successfully implemented by taking into account a different doping at contacts with respect to the bulk channel and partial charge pinning at the contacts. We finally show that a double-dip enhanced hysteresis can conveniently be exploited to build graphenebased memory devices. References [1] A. Di Bartolomeo et al., Nanotechnology 22 (2011) 275702 (8pp)

Figure 1: (a) Transfer characteristic of a GFET with hysteresis and double dip. (b) Band diagrams of graphene between source and drain and position of the Fermi level at different VGS for different gate voltages. For floating gate, the double cone, close to the contacts, is shifted upward with respect to the one in the bulk channel to account for the p-type graphene due to transfer of electrons from graphene to the Cr/Au leads.

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Figures

Roll to Roll Printing of Aqueous Pristine Graphene Dispersions

N. Graddage , D. Parviz , T.C. Claypole , D.T. Gethin , M.J. Green 1 2

Welsh Centre for Printing and Coating, Swansea University, UK Dept. Of Chemical Engineering, Texas Tech University, TX, USA 478018@swansea.ac.uk

Since the isolation and observation of graphene[1] there have been a vast number of proposed applications for the material. With applications ranging from photovoltaic devices[2], touchscreens[3], energy storage[4] and transistor electronics[5] the potential for graphene appears almost limitless. However the commercial realisation of each application depends on graphene being produced and deposited in a cheap, accurate and rapid manufacturing environment. This work aims to develop a stable water based graphene solution and then deposit the graphene using a number of printing methods. Graphene production techniques can be classified into two types; top down and bottom up. Bottom up production describes the growth of graphene using epitaxial or CVD growth techniques. This tends to result in high quality films and growth can be patterned precisely. However growth techniques tend to require high temperatures and catalyst materials, limiting the choice of substrates. Bottom up growth methods tend to require environments and timescales that are unsuitable for roll to roll production techniques, though batch roll lamination of large area CVD grown graphene sheets has been demonstrated.

ABSTRACTS

Top down production techniques tend to separate the graphene sheets from a graphite precursor. This can be performed in many ways, the most famous being the mechanical exfoliation method[1]. Other separation methods include sonication in suitable solvents[6], reduction of graphene oxide and non covalent functionalization of graphene in solution by stabilizers. Unlike bottom up methods, top-down production methods allow for direct preparation of graphene dispersions or mass production of graphene powders, which can then be dispersed in suitable solvents and deposited on proper substrate for further device manufacturing. This will result in lower production costs and timescales, but at the same time the conductivity and optical performance of graphene films may be hindered due to an increased contact resistance between multilayers of graphene. However this method will still be suitable for many applications, such as catalyst layers in dye sensitized photovoltaic cells which require large available surface areas for which graphene powder will be preferable to large area flakes. The initial stage of this research focused on the production of stable graphene solutions while avoiding the use of conventional stabilizers such as surfactants. In first step, an aqueous solution of expanded graphite and functionalized pyrene derivatives (or “π-π stackers”) was sonicated to increase the interlayer spacing of graphene sheets. These stacker molecules adsorb on the surface of graphene layers through π-π interactions between their aromatic basal planes. They prevent reaggregation of graphene sheets by inducing steric and electrostatic repulsion forces between separated sheets[7,8]. The process was followed by centrifugation step to remove undispersed graphite from the final graphene solution. Compared to conventional stabilizers such as surfactants, these pyrene derivatives yield higher concentrations of graphene per mass of stabilizer. These solutions were then tested with a variety of solution deposition methods to assess their suitability for further device production. Initial tests focused on inkjet printing, a method that is ideal for low viscosity solutions but limiting with respect to flake size due to the jetting nozzle diameter. The solution was characterised to identify suitability for inkjet printing and it was found that the viscosity was below

recommended specifications and the surface tension was too high, however the solution was jettable. An image of an inkjet print onto a Si wafer is shown in figure 1. Strategies for further optimisation of the fluid for inkjet printing have been identified and further research is ongoing. The solution was also deposited using a flexographic printing technique. This technique allows for higher speeds than inkjet printing at the expense of feature resolution. Traditionally flexographic inks need to have higher viscosities than inkjet inks, however techniques have been developed to partially overcome these limitations and enable the flexographic printing of homogenous features using low viscosity inks. This will allow minimisation of additive usage in the ink, which will tend to have a detrimental effect on the electronic properties. Applying these techniques allowed features to be successfully printed. Analysis of the electronic performance of these prints is also ongoing. In conclusion, stable water based graphene dispersion has been produced using pyrene derivatives instead of surfactants. This dispersion has then been deposited using two contrasting printing methods. This work demonstrates the dispersion suitability for use in high speed, roll to roll device manufacture, which is one of the keys to unlocking the commercial promise of graphene. References [1] Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V. & Firsov, A. A., Electric Field Effect in Atomically Thin Carbon Films, Science, 306 (2004) 666-669. [2] Pang, S.; Hernandez, Y.; Feng, X.; M端llen, K., Graphene as Transparent Electrode Material for Organic Electronics, Adv. Mater., 23 (2011) 2779-2795. [3] Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J.-S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Ri Kim, H.; Song, Y. I.; Kim, Y.-J.; Kim, K. S.; Ozyilmaz, B.; Ahn, J.-H.; Hong, B. H. & Iijima, S., Roll-to-roll production of 30-inch graphene films for transparent electrodes, Nat Nano, 5 (2010) 574-578. [4] Geim, A. K., Graphene: Status and Prospects, Science, 324 (2009) 1530-1534. [5] Torrisi, F.; Hasan, T.; Wu, W.; Sun, Z.; Lombardo, A.; Kulmala, T.; Hshieh, G.W.; Jung, S.J.; Bonaccorso, F.; Paul, P.J.; Chu, D.P.; Ferrari, A.C.; Ink-Jet Printed Graphene Electronics, arXiv:1111.4970v1 [cond-mat.mtrl-sci] (2011). [6] Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; 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., High-yield production of graphene by liquid-phase exfoliation of graphite, Nat Nano, 3 (2009) 563568. [7] An, X.; Simmons, T.; Shah, R.; Wolfe, C.; Lewis, K. M.;Washington, M.; Nayak, S. K.;Talapatra, S.; Kar, S., Stable Aqueous Dispersions of Noncovalently Functionalized Graphene from Graphite and their Multifunctional HighPerformance Applications. Nano Letters, 10 (2010) 4295-4301. [8] Zhang, M.; Parajuli, R. R.; Mastrogiovanni, D.; Dai, B.; Lo, P.; Cheung, W.; Brukh, R.; Chiu, P. L.; Zhou, T.; Liu, Z.; Garfunkel, E.; He, H., Production of Graphene Sheets by Direct Dispersion with Aromatic Healing Agents. Small, 6 (2010) 1100-1107.

Figure 1: 6.5x optical image of aqueous graphene solution inkjet printed onto Si wafer.

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Interaction effects in graphene heterostructures

Francisco Guinea Instituto de Materiales de Madrid. CSIC, Spain

Recent experiments have shown a variety of effects induced by the electron-electron interaction in graphene single layers and bilayers, as well as in graphene heterostructures [1-5] made up by combining layers of graphene and boron nitride. We analyze the electron-hole pairs and plasmons of these structures. These excitations modify the electron-electron interactions, and they can lead to the superconducting pairing at observable carrier concentrations and temperatures [6,7].

References

ABSTRACTS

[1] A. S. Mayorov, R. V. Gorbachev, S. V. Morozov, L. Britnell, R. Jalil, L. A. Ponomarenko, P. Blake, K. S. Novoselov, K.Watanabe, T. Taniguchi, and A. K. Geim, Nano Lett. 11, 2396 (2011). [2] L. A. Ponomarenko, A. K. Geim, A. A. Zhukov, R. Jalil, S. V. Morozov, K. S. Novoselov, V. V. Cheianov, V. I. Fal'ko, K. Watanabe, T. Taniguchi, and R. V. Gorbachev, Nature Phys. 7, 958 (2011). [3] G.-H. Lee, Y.-J. Yu, C. Lee, C. Dean, K. L. Shepard, P. Kim, and J. Hone, Appl. Phys. Lett. 99, 243114 (2011). [4] L. Britnell, R. V. Gorbachev, R. Jalil, B. D. Belle, F. Schedin, M. I. Katsnelson, L. Eaves, S. V. Morozov, N. Peres, J. Leist, A. K. Geim, K. S. Novoselov, and L. A. Ponomarenko (2011), Science 335, 947 (2012). [5] L. Britnell, R. V. Gorbachev, R. Jalil, B. D. Belle, F. Schedin, M. I. Katsnelson, L. Eaves, S. V. Morozov, A. S. Mayorov, N. Peres, A. H.Castro Neto, J. Leist, A. K. Geim, L. A. Ponomarenko and K. S. Novoselov (2012), arXiv:1202.0735. [6] B. Uchoa and A. H. Castro Neto, Phys. Rev. Lett. 98, 146801 (2007), [7] W. Kohn and J. M. Luttinger, Phys. Rev. Lett. 15, 524 (1965),

Mechanism of Growth of Graphene Grains on Copper during Low Pressure Chemical Vapor Deposition

Zheng Han, Amina Kimouche, Adrien Allain, Hadi Arjmandi-Tash, Antoine Reserbat-Plantey, Sﾃｩbastien Pairis, Valﾃｩrie Reita, Nedjma Bendiab, Johann Coraux & Vincent Bouchiat Institut Nﾃ右L, CNRS & Universitﾃｩ Joseph Fourier, BP166, F-38042 Grenoble Cedex 9, France zheng.han@grenoble.cnrs.fr

Graphene grown by chemical vapor deposition (CVD) on Cu is very promising for future graphene applications, as it meets the two requirements for batch production, namely: 1) large size and self limitation to a single-layer of graphene and 2) easy transfer onto arbitrary substrates [1-4]. New insights for controlling CVD processes, e.g. leading to dendritic growth of graphene flakes [5], or allowing for controlling the size of hexagonal islands [6], were recently demonstrated. Although extensive studies have been conducted on the CVD of graphene on Cu, some of the processes involved during growth remain to be elucidated. Two important remaining issues are: (1) the parasitic formation of multilayer regions [7-8], and (2) the occurrence of both hexagonal-shaped and dendritic flakes.

Interestingly, the larger lobe-shaped islands are very likely comprising in their center a two- (or even more) layer region (Figure 2) as already observed in previous reports [8,11,12]. The shape and size of the second layer centered in the large islands are strikingly similar to that of smaller islands in between larger islands. This bimodality in island shapes and sizes can be explained by the fact that the larger islands are the result of surface growth from an adatom carbon gas at high temperature, and that the smaller islands develop upon cooling down after growth, via segregation of carbon atoms stored at Cu defects extending out of the surface plane (Figure 3b). Moreover, a recent study suggests that the central layer is underneath the first larger layer [13]. Actually, it is known that multilayer and inhomogeneous graphene results from enhanced carbon segregation, which is favored at defects such as screw dislocations or grain boundaries [14]. In the light of all above, there are two routes to suppress these carbon inhomogeneities: either by suppressing the surface defects via graphene deposition on top of high quality metallic surfaces (single crystal metal, epitaxial thin films), or by keeping standard low-cost copper foil but depleting nucleation at defects upon cooling.

ABSTRACTS

In this work, we report on a systematic study of the CVD growth mechanism of graphene on Cu under low gas pressure (1 mbar total pressure of a Ar/H2/CH4 mixture). Before graphene islands merge into a continuous layer, various shapes can be found for graphene flakes, ranging from hexagonal ones to flowerlike dendritic ones, depending on the growth conditions (inset of Figure 1). Besides flowershaped islands coexist with smaller ones, hexagonally-shaped (Figure 2a). We found no indication for two preferential crystallographic orientations which would each correspond to one type (larger or smaller) of islands. Neither do we find any correlation between the island size and the distance to the nearest neighbor island. We analyzed the roughness of the edges of graphene islands with different sizes by measuring the perimeter of the islands against their area (Figure 1). A plot of hexagonal shape is shown in Figure 1 as a reference. One can see that the smallest islands have almost hexagonal shape, and the larger the islands, the more they diverge from the hexagonal shape, which reveals the that graphene growth begins with the nucleation of hexagonal islands latter evolving into dendritic lobe-shaped islands, which is illustrated by our model in Figure 3a, as well as the model proposed in other works [9,10].

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

X. Li, et al Science 324 (2009) 5932. K. S. Kim, et al Nature 457 (2009) 706. S. Bae, et al Nat. Nanotech. 5 (2010) 574. D. R. Cooper, et al arXiv: 1110.6557v1 X. Li, et al J. Am. Chem. Soc. 133 (2011) 2816 Q. K. Yu, et al Nature Materials 10 (2011) 443 K. Yan, et al NanoLett. 11 (2011) 1106 A. W. Robertson, et al NanoLett. 11 (2011) 1182 S. Nie, et al Phys. Rev. B 84 (2011) 155425 C. Hwang, et al J. Phys. Chem. C, (2011), DOI: 10.1021/jp205980d. I. Vlassiouk, et al ACSnano 5 (2011) 6069 G. X. Ni, et al ACSnano DOI: 10.1021/nn203775x S. Nie, et al arXiv: 1202.1031v1 S. Yoshii, et al NanoLett. 11 (2011) 2628

Figures

ABSTRACTS

Figure 1: Plot of the perimeter of graphene islands as a function of their area. Squares represent for graphene islands prepared by CVD growth. The green dots correspond to perfect hexagonal islands. Inset: a, b, c, are SEM images of graphene islands found on one single Cu foil obtained via CVD growth (2 sccm CH4, 20 min, 1 mbar), which presents three different stages of the growth: start of the hexagonal nucleation, diffusive lobe-shape flower, flower with a “seed” in the center. Scale bars for the inset are 3 μm.

Figure 2: a) Scanning electron micrograph images of graphene flakes grown on Cu under the condition of 1000 oC, 2 sccm CH4, 1 mbar, for 20 minutes. Scale bar is 10 μm; b) AFM image of one of the flowers shown in a. A profile of the cross section of this flower is given below.

Figure 3: a) A simple model showing the formation of graphene islands from the beginning of their nucleation to the final continuous layer; b) Schematic of the flower centers formed at the defect sites during cooling down.

Production and Applications of Graphene for Large-Area Electronics

Byung Hee Hong Department of Chemistry, Seoul National University, Seoul 151-747, Korea byunghee@skku.edu

Graphene has been attracting tremendous attention owing to its fascinating physical properties including quantum electronic transport phenomena, ultrahigh mobility, superb elasticity, thermal conductivity and mechanical strength. There have been many efforts to utilize these outstanding properties of graphene for macroscopic applications such as transparent conducting films useful for flexible/stretchable electronics. However, the scale and the quality graphene need to be further enhanced for practical applications by developing more efficient synthesis, transfer and doping methods. In this talk, the recent advances in large-area graphene synthesis/doping/transfer will be reviewed first, and the various applications to graphene-based large-area electronics will be discussed. References

ABSTRACTS

[1] S. Bae et al. Nature Nanotech. 5, 574 (2010). [2] K. S. Kim et al. Nature 457, 706 (2009).

Korean Graphene Research Activities and Roadmap

Byung Hee Hong Department of Chemistry, Seoul National University, Seoul 151-747, Korea byunghee@skku.edu

ABSTRACTS

Recently, Korean government has approved a plan for commercializing graphene technologies, including graphene-based touch panels, organic light-emitting diodes (OLEDs), electro-chromic smart windows, secondary batteries for electronic vehicles, high-voltage high-power supercapacitors, ultra-light and strong composites, high-performance gas barrier films, electro-magnetic interference shielding, and environmentally friendly anti-oxidation steel plates. These items have been carefully selected considering economic efficiency and technological feasibility. In addition, Korea is also planning a “Korean Graphene Hub” project that is focusing on the fundamental sciences of graphene and related 2D materials, separately. In this talk, the brief history, recent status, and prospect of Korea’s graphene projects will be introduced, and discuss how we can harmonize the world-wide graphene projects based on international collaboration rather than competition.

Preparation and Application of Chemically Functionalized Graphene

Mark C. Hersam Department of Materials Science and Engineering; Northwestern University;2220 Campus Drive, Evanston, IL 60208-3108 http://www.hersam-group.northwestern.edu/

Graphene has emerged as one of the leading materials in condensed matter physics due to its superlative electrical and mechanical properties. With an eye towards expanding its functionality and applications, this talk will highlight our latest efforts to tailor the surface chemistry of graphene via chemical functionalization [1]. At the molecular scale, we employ ultra-high vacuum (UHV) scanning tunneling microscopy (STM) and conductive atomic force microscopy (cAFM) to characterize chemically modified epitaxial graphene on SiC(0001) [2,3]. For example, a suite of perylene-based molecules form highly ordered self-assembled monolayers (SAMs) on graphene via gas-phase deposition in UHV [4,5]. Due to their noncovalent bonding, these SAMs preserve the superlative electronic properties of the underlying graphene while providing uniform and tailorable chemical functionality [6]. In this manner, disparate materials (e.g., high-k gate dielectrics) can be seamlessly integrated with graphene, thus enabling the fabrication of capacitors, transistors, and related electronic/excitonic devices [7]. Alternatively, via aryl diazaonium chemistry, functional polymers can be covalently grafted to graphene [8], while exposure to atomic oxygen in UHV enables chemically homogeneous and thermally reversible epoxy functionalization of graphene [9]. In addition to presenting opportunities for graphene-based chemical and biological sensing, covalent grafting allows local tuning of the electronic properties of the underlying graphene. Beyond UHV STM characterization, this talk will also delineate our most recent efforts to exploit chemically functionalized graphene in technologically significant applications. Specific examples include the utilization of graphene oxide as an interfacial layer in organic photovoltaic devices [10], solutionprocessed graphene for transparent conductors [11-13] and flexible GHz transistors [14], pluronicdispersed graphene for in vivo biomedical applications [15,16], and graphene-titania nanocomposites as photocatalysts for the production of solar fuels from carbon dioxide [17].

Q. H. Wang and M. C. Hersam, MRS Bulletin, 36, 532 (2011). J. A. Kellar, et al., Applied Physics Letters, 96, 143103 (2010). J. M. P. Alaboson, et al., Advanced Materials, 23, 2181 (2011). Q. H. Wang and M. C. Hersam, Nature Chemistry, 1, 206 (2009). Q. H. Wang and M. C. Hersam, Nano Letters, 11, 589 (2011). J. D. Emery, et al., Surface Science, 605, 1685 (2011). J. M. P. Alaboson, et al., ACS Nano, 5, 5223 (2011). Md. Z. Hossain, et al., Journal of the American Chemical Society, 132, 15399 (2010). Md. Z. Hossain, et al., Nature Chemistry, in press, DOI: 10.1038/nchem.1269 (2012). I. P. Murray, et al., Journal of Physical Chemistry Letters, 2, 3006 (2011). A. A. Green and M. C. Hersam, Journal of Physical Chemistry Letters, 1, 544 (2010). A. A. Green and M. C. Hersam, Nano Letters, 9, 4031 (2009). Y. T. Liang and M. C. Hersam, Journal of the American Chemical Society, 132, 17661 (2010). C. Sire, et al., Nano Letters, in press, DOI: 10.1021/nl203316r (2012). M. C. Duch, et al., Nano Letters, 11, 5201 (2011). J.-W. T. Seo, et al., Journal of Physical Chemistry Letters, 2, 1004 (2011). Y. T. Liang, et al., Nano Letters, 11, 2865 (2011).

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

ABSTRACTS

References

Tayloring the graphene/silicon carbide interface: a material system for monolithic wafer-scale electronics

Stefan Hertel , Daniel Waldmann , Johannes Jobst , Sergey Reshanov , Adolf Schöner , 1 1 Michael Krieger , Heiko B. Weber 1 2

Chair of Applied Physics, University of Erlangen-Nuremberg, Staudtstraße 7, 91058 Erlangen, Germany ACREO AB, Electrum 236, 16440 Kista, Sweden Stefan.Hertel@physik.uni-erlangen.de

Graphene has many outstanding electronic properties and a vision of post-silicon electronics based on graphene is discussed. However, due to the absence of an electronic band gap transistors with high on/off ratio are still lacking[1]. Consequently, graphene circuits are currently limited to analogue amplification[2] and further modifications are needed for logic applications. Many efforts have been undertaken to establish a gap in graphene devices, with a band gap induced by bilayer graphene, spatial confinement, localization and chemical modification, resulting in rather small effects remote from technical requirements. For wafer based applications, we consider epitaxial graphene on silicon carbide (0001) as the first choice[3]. We propose a concept that monolithically employs the entire system epitaxial graphene, consisting of graphene, silicon carbide, and their common interface. For a transistor, graphene can be used as source, drain and gate electrode. The wide band gap semiconductor substrate silicon carbide forms the channel. Finally, two differently tailored interfaces introduce transistor functionality. The result is an epitaxial graphene transistor with high on/off ratio exceeding 104(see Fig. 1). Depending on the underlying substrate, both normally-on and normally-off operation is possible. The concept’s particular strength is its capability for integration: within the same processing effort many epitaxial graphene transistors can be combined and complex circuits can be designed. In principle any logic functionality can be implemented.

References

ABSTRACTS

[1] Schwierz, F., Nature Nanotachnology, 5 (2011) 487-496. [2] Lin, Y.-M.; Valdes-Garcia, A.; Han, S.-J.; Farmer, D. B.; Meric, I.; Sun, Y.; Wu, Y.; Dimitrakopoulos, C.; Grill, A.; Avouris, P.; Jenkins, K. A., Science, 332 (2011) 1294-1297. [3] Emtsev, K. V.; Bostwick, A.; Horn, K.; Jobst, J.; Kellogg, G. L.; Ley, L.; McChesney, J. L.; Ohta, T.; Reshanov, S. A.; Rohrl, J.; Rotenberg, E.; Schmid, A. K.; Waldmann, D.; Weber, H. B.; Seyller, T., Nature Materials, 8 (2009) 203-207. [4] Jobst, J.; Waldmann, D.; Speck, F.; Hirner, R.; Maude, D. K.; Seyller, T.; Weber, H. B., Solid State Communications, 151 (2011) 1061-1064. [5] Gerhard Pensl, F. C., Thomas Frank, Michael Krieger, Sergey Reshanov, Frank Schmid, Michael Weidner, International Journal of High Speed Electronics and Systems, 15 (2005) 705-745. [6] Riedl, C.; Coletti, C.; Iwasaki, T.; Zakharov, A. A.; Starke, U., Physical Review Letters, 103 (2009) 246804.

Figures

ABSTRACTS

Figure 1: Figure 1a shows a scheme of our device. The graphene/silicon carbide interface is tailored in two different ways resulting in contact graphene with ohmic contact to the semiconducting layer and gate graphene forming a Schottky contact. With these components we define a MeSFET-like transistor with silicon carbide as the semiconductor and graphene playing the role of both contact and gate metal. Figure 1b displays the transfer characteristics for various temperatures. On/off ratios were determined between VTG = 0V and the minimum ID value (indicated by arrows). The largest on/off contrast is achieved at T = 220 K. Improved surface quality, resulting in more homogeneous Schottky barriers, is expected to further reduce leakage currents and to extend high on/off performance to room temperature and beyond.

Scattering mechanisms that cause 1/f noise in graphene

A. A. Kaverzin, A. S. Mayorov, A. Shytov, D. W. Horsell School of Physics, University of Exeter, Exeter, EX4 4QL, UK D.W.Horsell@exeter.ac.uk

100

ABSTRACTS

We experimentally study the effect of different scattering potentials on the 1/f noise observed in graphene devices on silica and silicon nitride substrates. The noise in nominally identical devices is seen to behave in two distinct ways as a function of carrier concentration, changing either monotonically or nonmonotonically. We attribute this to the interplay between long- and short-range scattering mechanisms. Water was found to significantly enhance the noise magnitude and change the type of the noise behaviour. By using a simple model, we show that water is a source of long-range scattering. Its presence on the graphene surface was found to increase the noise by an order of magnitude, yet cause a comparatively insignificant change in the resistance, which demonstrates that low-frequency noise and resistance in graphene can be determined by different scattering mechanisms. We have also shown that the 1/f noise at the Dirac point and at finite concentration originates from different sources of scattering and most likely from different fluctuation mechanisms.

Impact of Short Range Scattering in Graphene Electronics

Allen Hsu, Ki Kang Kim, Daniel Nezich, Rachel Luo, Han Wang, Jing Kong, Tomas Palacios Massachusetts Institute of Technology, 60 Vassar Street, Cambridge, U.S.A. allenhsu@mit.edu

The extremely high carrier mobility of graphene, in excess of 100,000 cm2V-1s-1 [1], has inspired a large number of new opportunities for this amazing material. Some examples, include ultra-thin-body graphene transistors potentially enabling radio frequency (RF) circuits operating in the terahertz regime, graphene interconnects with low resistance and capacitance to replace copper, and a cost-effective replacement for Indium Tin Oxide (ITO) transparent conductive electrodes in light emitting diodes (LEDs), solar cells and flat panel displays [2-4]. In spite of these applications, the predominant interest in graphene research has focused primarily on studying the low carrier density (ns) transport regime < 1-2x1012 cm-2, where record mobility values have been achieved. However for almost all applications of graphene, typically operating carrier densities are greater than 2x1012 cm-2, especially in applications of graphene operating as a transparent conductor or in radio frequency transistors where large sheet charges are necessary for adequate gain. While low carrier concentration transport studies have allowed for many fundamental studies of relativistic physics and ballistic transport in devices, transport studies at higher carrier densities are as important for many commercial applications. Therefore, this work focuses on examining the transport limiting mechanisms in graphene and their implications on three different device applications (1) transparent conductive electrodes, (2) graphene-metal contact resistance, and (3) graphene interconnects. Through Hall Measurements on graphene grown by chemical vapor deposition, we examine the high carrier density mobility degradation due to short range scatters. To isolate the physical origin of short range scattering in graphene, we have examined the mobility of various growth conditions comparing copper and nickel synthesized graphene. Furthermore, we compared the effect of various dopants, such as Aluminum oxide, on carrier mobility and extracted the ratio between the density of charged impurity and short range scatters from our data as well as values from literature [5][6].

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[1] K. Bolotin, K. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, H. Stromer, Solid State Communications, 9 (2008) 351. [2] R. Murali, K. Brenner, Y. Yang, T. Beck, J.D. Meindl, IEEE Electron Device Letters, 6 (2009) 611. [3] S. De, J.N. Coleman, ACS Nano, 5 (2010) 2713. [4] J.S. Moon, D. Curtis, M. Hu, D. Wong, C. McGuire, P.M. Campbell, G. Jernigan, J.L. Tedesco, B. VanMil, R. MyersWard, C. Eddy, D.K. Gaskill, IEEE Electron Device Letters, 6 (2009) 650. [5] C.R. Dean, A.F. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, K. Watanabe, T. Taniguchi, P. Kim, K.L. Shepard, J. Hone, Nature Nanotechnology, 10 (2010) 722. [6] L. A. Ponomarenko, R. Yang, T.M. Mohuiddin, M.I. Katsnelson, K. S. Novoselov, S. V. Morozov, A. A. Zhukov, F. Schedin, E. W. Hill, A. K. Geim, Physics Review Letters, 20 (2009) 206603.

ABSTRACTS

References

Figures

µ (cm /Vs)

LPCVD Cu−G APCVD Ni−G LPCVD Cu−G + Al(ox) hBN− HOPG SLG (Columbia) SiC−Si Face (NRL) 1/µ0 + ns/C (C=2.0e+016,µ0 =1.0e+004) 1/µ0 + ns/C (C=1.0e+016,µ0 =5.0e+003) 1/µ + n /C (C=1.0e+017,µ =4.8e+004) 0

n (1/cm ) s

Figure 1: Mobility versus Carrier Concentration for various films. (x) – low pressure CVD graphene grown on Cu (Δ) – ambient pressure graphene grown on Nickel (●) LPCVD Graphene on Copper with Al(ox) layer (○) HOPG on hBN [5] (+) SiC Si Face [6] 3

LPCVD Cu−G LPCVD Cu−G + Al(ox) hBN−HOPG SLG (1−hBN/1−SLG) 1/µ + n /C (C=2.0e+016,µ =1.0e+004) 0

1/µ + n /C (C=1.0e+016,µ =5.0e+003) 0

1/µ + n /C (C=1.0e+017,µ =4.8e+004) 0

ρ (µΩ−cm)

Cu 0

10 11 10

ns (1/cm )

102

ABSTRACTS

Figure 2: Specific Resistivity plotted as a function of carrier concentration. Copper values were obtained from literature [2].

Self-Assembled Graphene Nanosacks

Yantao Chen, Fei Guo, Ashish Jachak, Sang-Pil Kim, Dibakar Datta, Jingyu Liu, Indrek Kulaots, Charles Vaslet, Hee Dong Jang, Jiaxing Huang, Agnes Kane, Vivek B. Shenoy, Robert H. Hurt Brown University, Providence, Rhode Island, USA Northwestern University, Evanston, Illinois, USA Robert_Hurt@brown.edu

Graphene oxide (GO) is a promising giant molecular precursor for the creation of new carbon materials, because it can be aligned, stacked, folded, or otherwise assembled in the colloidal state into complex twoor three-dimensional structures [1-6] and then reduced to carbon. Here we show that monolayer graphene oxide can be co-suspended with a variety of second components in dilute aqueous phases and ultrasonically nebulized and dried/heated to produce electron transparent graphene “sacks” that encapsulate an internal cargo.

103

We propose that the filled graphene nanosacks are a self-assembled structure that occurs by spontaneous segregation of the sack and filler into a core-shell symmetry. There is a thermodynamic driving force for GO to adsorb at the liquid-vapor interface, and previous studies have reported the formation of GO surface films on drying droplets [3]. In addition, GO has a large hydrodynamic radius (750 nm) and low diffusion coefficient, and as a result is overtaken and scavenged by the receding water-air interface during droplet drying. To better understand formation mechanisms, we carried out molecular dynamics (MD) simulations of droplet drying in the presence of monolayer graphene (Fig. 2a) and graphene oxide (Figure 2b). For graphene there is a noticeable gap at the water interface, and the droplet appears to template or guide the graphene into a scroll structure during drying. We believe that weak van der Waals forces in the water/graphene system [9] allow graphene to slide on the droplet surface, which enables this “guide and glide” assembly mode. Graphene oxide in contrast clings to the droplet surface through hydrogen bond interactions and is dragged inward as the droplet volume is reduced by drying (“cling and drag” mechanism). These simulations together with calculations of diffusion rates for the sacks and fillers lead to the conceptual model shown in Fig. 3 for the formation of filled graphene nanosacks.

ABSTRACTS

Graphene oxide was prepared by a modified Hummers method and purified by a two-step acid-acetone wash [7]. Suspensions were ultrasonically aerosolized to produce a mist of microdroplets suspended in a gas flow, which were dried in situ by heating (70-600 C). When graphene oxide is the only component in suspension, the products are crumpled graphene nanoparticles similar to those reported recently [5,8]. In the presence of a second component, however, the products are “filled graphene nanosacks” (Fig. 1). At low filler concentrations, the crumpled nanoparticle structure is preserved but the second component is found inside a thin graphene shroud (Fig. 1a). At higher filler concentrations, we still see a graphene shroud (Fig. 2b), but the graphene has fewer creases and the structure resembles a sack with a cluster of filler (Ag nanoparticles) as contents or “cargo”. The filler appears to act as a scaffold that mechanically supports the graphene sack and prevents complete collapse to crumpled graphene. We have also fabricated filled graphene nanosacks using cargos that include hydrophilic, arylsulfonated carbon black nanoparticles (Fig. 1f), fluorescein-sodium dye, and salmon sperm DNA. If the chosen filler has a high atomic number, it can be directly visualized inside the sack by SEM (Fig. 1a, b). Organic or carbon-based fillers are not easily observable, but their presence is reflected in the swollen sack structure (Fig.1f), and can be seen by TEM.

We currently envision a broad set of technological uses for filled graphene nanosacks. Many potential applications derive from the ability of sacks to isolate nanoparticle cargos from biological tissue or the natural environment where particle release is undesirable due to human or ecological toxicity. Inside the sacks, nanoparticle cargos can be isolated from biological target molecules associated with toxicity, while still exhibiting useful photonic, magnetic, or radiological functions. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

Ruoff, R. Nat. Nanotechnol. 3, (2008) 10. Compton, O. C.; Nguyen, S. T. Small 6 (2010) 711. Guo, F.; Kim, F.; Han, T. H.; Shenoy, V. B.; Huang, J.; Hurt, R. H. ACS Nano, 5 (2011) 8019. Guo, P.; Song, H.; Chen, X. J. Mater. Chem. 20, (2010) 4867. Luo, J.; Jang, H. D.; Sun, T.; Xiao, L.; He, Z.; Katsoulidis, A. P.; Kanatzidis, M. G.; Gibson, J. M.; Huang, J. ACS Nano 5 (2011) 8943. Zhou, X.; Wang, F.; Zhu, Y.; Liu, Z. J. Mater. Chem. 21 (2011), 3353. Kim, F.; Luo, J.; Cruz-Silva, R.; Cote, L. J.; Sohn, K.; Huang, J. Adv. Funct. Mater. 20 (2010) 2867. Ma, X.; Zachariah, M. R.; Zangmeister, C. D. Nano Lett. in press, 2012. Leenaerts, O.; Partoens, B.; Peeters, F. M. Phys. Rev. B 79 (2009) 235440.

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Figure 1: Filled graphene nanosacks from drying binary microdroplet suspensions. (a) SEM of Agnanoparticle-filled sacks at low loading (Ag:GO mass ratio 0.06); (b,c,d) SEM/TEMs of silver nanoparticles at higher loading (Ag:GO mass ratio + 2); (e) Time-resolved release of Ag in 5 mM pH 4 acetate buffer from gradual oxidation of encapsulated nano-silver particles, vs. free Ag nanoparticle control to show the inhibiting effect of encapsulation, (f) hydrophilic, aryl-sulfonated carbon black (CB) nanoparticles at high loading (CB:GO ratio 2).

Figure 2: Mechanisms of nanosack formation. (a,b) Molecular dynamics simulations of waterdroplet-actuated scrolling, folding, or collapse for (a) monolayer graphene, which scrolls through a “guide and glide” mechanism; (b) Monolayer GO which closes and collapses by a “cling and drag” mechanism.

Figure 3: Conceptual model for the colloidal selfassembly of filled graphene nanosacks. Microdroplet drying leads to graphene oxide adsorption and scavenging at the receding gaswater interface, while the second component diffuses away from the interface becomes incorporated in the final nanoparticle core. Colloidal segregation is followed by sack closure and collapse by capillary forces. High filler loading acts as a scaffold to prevent complete sack collapse.

Transport phenomena in nanostructured graphene

Antti-Pekka Jauho Center for Nanostructured Graphene (CNG), Department of Micro and Nanotechnology, Technical University of Denmark, Kongens Lyngby, DK 2800 Denmark Antti-Pekka_Jauho@nanotech.dtu.dk

In order to realize many of the promises that graphene may fulfill, the pristine sheet must be modfied so as to display a band gap, at least in certain regions in space. This can be achieved, e.g., by a selective adsorption of adatoms, by cutting the graphene sheet into a nanoribbon, or by applying a transverse electric field to a bilayer graphene. Here we describe yet another route: a regular perforation of the graphene sheet, dubbed as graphene antidot lattice (GAL). Our group developed this idea in 2008 [1], and since then many groups have followed route, either independently, or by using the concepts we introduced. We describe the basic theoretical ideas, review the experimental situation and some aspects of the rapidly growing theoretical literature, and report on our recent simulations of charge and thermal transport in finite GALs [2]. We also address how very large systems of nanostructured graphene may be amenable to simulations using first-principles input [3].

References

105

ABSTRACTS

[1] T. G. Pedersen, C. Flindt, J. Pedersen, N. A. Mortensen, A. P. Jauho, and K. Pedersen, Phys. Rev. Lett. 100, 136804 (2008) [2] T. Gunst, T. Markussen, A. P. Jauho, and M. Brandbyge, Phys. Rev. B 84, 155449 (2011) [3] A. Uppstu, K. Saloriutta, A. Harju, M. Puska, and A. P. Jauho, Phys. Rev. B 85, 041401 (2012) (RC)

Raman spectroscopy of electrochemically doped 1-LG and 2-LG

a,b

Martin Kalbac , Jing Kong , Ladislav Kavan and Mildred S. Dresselhaus

b,c

J. HeyrovskĂ˝ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., DolejĹĄkova 3, CZ-18223 Prague 8, Czech Republic b Department of Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts 02139, USA c Department of Physics, MIT, Cambridge, Massachusetts 02139, USA kalbac@jh-inst.cas.cz

The doping of graphene can be realized chemically, electrochemically or by electrostatic charging. The electrochemical doping can be easily controlled and it allows to reach relatively high doping levels of graphene. The doping of graphene leads to a shift of the Fermi level and therefore it represents a simple way to control graphene electrical and optical properties. These changes can be monitored and studied using Raman spectroscopy. In our study we compared the influence of electrochemical doping on the Raman spectra of one-layer and two-layer graphene. In the case of two layer graphene we prepared isotopically engineered sample where one layer of graphene was formed by 13C isotope while the second layer by 12C isotope. This approach allowed us to monitor charge distribution between the top and bottom layer which is important for prospective application of two layer graphene in electronic devices.

References

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[1] M. Kalbac,H. Farhat, J. Kong, P. Janda, L. Kavan, and M. S. Dresselhaus: Nanoletters, 11(5),1957-1963 (2011). [2] M. Kalbac,A. Reina-Cecco, H. Farhat, J. Kong, L. Kavan, and M. S. Dresselhaus: ACS Nano, 4 (10), 6055-6063 (2010).

Graphene – CdSe/ZnS quantum dots conjugated systems: charge transfer phenomena and their applications

Alexander V. Klekachev1,2, Inge Asselberghs1, Sergey N. Kuznetsov3, Johan Hofkens2, Marleen H. van der Veen1, Afshin Hadipour1, André L. Stesmans2, Marc M. Heyns1,2, Stefan De Gendt1,2 1

imec, Kapeldreef 75, B-3001 Leuven, Belgium Katholieke Universiteit Leuven, Celestijnenlaan 200d, B-3001 Leuven, Belgium 3 Petrozavodsk State University, Lenin av. 33, 185910, Petrozavodsk, Russia 2

alexander.klekachev@imec.be

Graphene possesses unique physical properties, due to its specific energy bands configuration, substantially different from that of materials traditionally employed in solid-state electronics. Among the variety of remarkable properties, high transparency in the visible-light range and low resistivity of graphene sheets are the most attractive ones for optoelectronic applications. Zero-dimensional colloidal semiconductor nanocrystals, known as quantum dots (QDs), attract immense attention in the field of photonics due to their size-dependent tunable optoelectronic properties. Their interaction with conductive surfaces is often reported to provide energy transfer instead of the charge transfer mechanism under presence of optical excitation. In this work, we demonstrate the role of single layer graphene (SLG) as an efficient charge transfer agent when conjugated with CdSe/ZnS core/shell quantum dots. We first demonstrate quenching of QDs photoluminescence (PL) on the graphene surface. Firgure 1a shows single-layer graphene flake exfoliated on a glass substrate followed by dispersion of QDs. Figure 1b reveals PL image of the same area obtained via confocal microscope setup. A PL quenching of ~10-15 is observed in correspondence of the SLG area, when compared to the SLG-free areas covered with QDs. Figure 1c confirms the presence of QDs on graphene area, however, at magnified intensity scale.

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Additionally, we demonstrate an efficient electron injection from graphene into CdSeZn or CdSe/ZnS layered nanocrystalline structures and the operation of the corresponding graphene-QDs light emiting diodes (LED). Typical structure of graphene-QDs LED device is shown in figure 3. A sandwich fabricated on top of thin gold film (anode) consists of hole transport layer PEDOT:PSS, QDs layer and the single graphene layer, acting as cathode. In order to fabricate large-scale devices with active area of 1x1 mm2 we utilize graphene layers synthesized via chemical vapor deposition (CVD) techniques. Graphene films are then transferred to target sandwich structures by traditional PMMA transfer process. Our devices reveal rather low threshold voltage of ~ 4.2 V and electroluminescence (EL) intensities up to ~300 cd/m2. We demonstrate that the latter parameter can be increased dramatically by adjusting the work-function of graphene electrode via molecular doping.

ABSTRACTS

We then characterize back-gated SLG field-effect transistors (FET) electrically during the QD excitation in order to investigate the nature of the interaction between SLG and the QDs. The transfer characteristics Ids vs. Vg of back-gated SLG field-effect transistors (FET) are shown in figure 2. The pristine SLG FET has its neutrality point (VNP) at ~ 0V. The same SLG FET is then sensitized by spin casting the QD solution. The transfer characteristics of the device are re-measured during excitation with laser of appropriate wavelength. A shift of the neutrality voltage VNP from –1.9 V towards more negative voltages is observed (VNP = –3.4 V), indicating that the electron accumulation in SLG is magnified by the interaction with the charge released by the optically excited QDs. The band alignment between SLG and the QDs allows electrons to be transferred by tunneling through the thin ZnS shell (figure 2b). The two conduction states (corresponding to the laser ON/OFF states) can be cycled reproducibly.

References

[1] Klekachev, A.V., et al., Electron accumulation in graphene by interaction with optically excited quantum dots. Physica E-Low-Dimensional Systems & Nanostructures, 2011. 43(5): p. 1046-1049.

Figures

Figure 1: (a) Optical image of a graphene flake exfoliated on a glass cover slip. (b) Photoluminescence image of the same graphene flake after treatment with QDs. (c) Photoluminescence of individual QDs on the graphene in the area, selected by blue rectangle under different intensity scale.

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Figure.2: (a) Transfer characteristics of a SLG FET in pristine conditions, after QD deposition, and during QD excitation by a laser light. The inset shows an optical microscope image of the device (scale bar: 2 Âľm). (b) Energy level diagram at the interface of the graphene-QD system under study

Figure.3: Schematic representation of graphene-QDs light emitting diode.

Graphene: a new platform for capturing and manipulating light at the nanoscale

Frank Koppens , Gerasismos Konstantatos , Michela Badioli , Johann Osmond , Louis 1 1 1 1 1 Gaudreau , Maria Bernechea , Pelayo Garcia de Arquer , Fabio Gatti , Marko Spasenovic , 2 2 2 2 3 Florian Huth , Jianing Chen , Pablo Alonso-GonzĂĄlez , Rainer Hillenbrand , Amaia Zurutuza , 3 3 4 4 Alba Centeno , Amaia Pesquera , Suko Thongrattanasiri and Javier Garcia de Abajo 1

ICFO, The institute of photonic Sciences, Barcelona (Spain) CIC nanoGUNE, San Sebastian CNM-IMB, Barcelona and GREMAN, Tours 4 IQFR-CSIC, Madrid 2 3

The ability to manipulate optical fields and the energy flow of light is central to modern information and communication technologies, as well as quantum information processing schemes. However, as photons do not possess charge, controlling them efficiently by electrical means has so far proved elusive. A promising way to achieve electric control of light could be through plasmon polaritons - coupled excitations of photons and charge carriers â&#x20AC;&#x201C; in graphene. In this two-dimensional sheet of carbon atoms, it is expected that plasmon polaritons and their associated optical fields can be readily tuned electrically by varying the graphene carrier density.

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The second part of the talk is devoted to a novel hybrid graphene-quantum dot photodetector [3] which exhibits a gain mechanism that can generate multiple charge carriers from one incident photon. Strong and tunable light absorption in the quantum-dot layer creates electric charges that are transferred to the graphene, where they recirculate many times due to graphene's high charge mobility and long trappedcharge lifetimes in the quantum-dot layer. We demonstrate a gain of 10^8 electrons per photon and a record-high responsivity of 10^7 A/W. Our devices also benefits from gate-tunable sensitivity and speed, spectral selectivity from the short-wavelength infrared to the visible, and compatibility with current circuit technologies.

ABSTRACTS

In the first part of this talk, I will discuss recent experiments revealing propagating optical plasmons in tapered graphene nanostructures, using near-field scattering microscopy with infrared excitation light [1]. The plasmonic field profiles are visible in real-space images with nanometer resolution. We find that the extracted plasmon wavelength is remarkably short - over 40 times smaller than the wavelength of illumination. We exploit this strong optical field confinement to turn a graphene nanostructure into a tunable resonant plasmonic cavity with extremely small mode volume [2]. The cavity resonance is controlled in-situ by gating the graphene, and in particular, complete switching on and off of the plasmon modes is demonstrated, thus paving the way towards graphene-based optical transistors. This successful alliance between nanoelectronics and nano-optics enables the development of unprecedented active subwavelength-scale optics and a plethora of novel nano-optoelectronic devices and functionalities, such as tunable metamaterials, nanoscale optical processing and strongly enhanced light-matter interactions for quantum devices and (bio)sensing applications.

References

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ABSTRACTS

[1] J. Chen, M. Badioli, P. Alonso-González, S Thongrattanasiri, F Huth, J Osmond, M. Spasenović, A. Centeno, A. Pesquera, P. Godignon, A. Zurutuza, N. Camara, J. Garcia de Abajo, R. Hillenbrand, F. Koppens, “Optical nanoimaging of gate-tuneable graphene plasmons”, arXiv 1202.4996 (2012) [2] F. Koppens, D. Chang, J. García de Abajo, “Graphene Plasmonics: A Platform for Strong Light–Matter Interactions”, Nano Letters 11, 3370–3377 (2011).  [3] G. Konstantatos, M. Badioli, L. Gaudreau, J. Osmond, M. Bernechea, P. Garcia de Arquer, F. Gatti, F. Koppens, “Hybrid graphene-quantum dot phototransistors with ultrahigh gain”, Nature Nanotechnology (in print). See also arXiv 1112.4730 (2011).

Twisting Graphene Nanoribbons into Carbon Nanotubes

1,2

Pekka Koskinen , Oleg O. Kit , Tuomas Tallinen , L. Mahadevan , Jussi Timonen 1 2

NanoScience Center, Department of Physics, University of Jyväskylä, 40014 Jyväskylä, Finland School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138 pekka.koskinen@iki.fi

For the past 20 years carbon nanotubes have been tributed as "rolled up graphene," though no one ever really did the rolling. Here we predict that, indeed, long and narrow graphene ribbons can be rolled into carbon nanotubes by means of twisting.[1] As today carbon nanotubes, along with many other nanomaterials, are made by atom-by-atom growth, the twisted proposal makes up a quite a different nano-fabrication method. The basic idea, however, is simple and easily grasped: just twist the ends of a strap of your backpack and watch the result (see figure). Therefore the mechanism, being classical in origin, is robust and valid in macro-, micro-, and nano-scales. Mechanism also enables experimental control, so it can be used to make carbon nanotubes controllably, to make various kinds of novel carbon nanotubules, to encapsulate molecules inside tubes, or to make tubules from ribbons made of other planar nanomaterials.

References [1] O. O. Kit, T. Tallinen, L. Mahadevan, J. Timonen, and P. Koskinen, Phys. Rev. B (Editor's Suggestion) [in print] (2012)

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Figure 1: Left: Snapshots from quantum simulation of a 24-Å wide zigzag graphene nanoribbon being twisted into a pristine (9,3) carbon nanotube. Right: The concept of tube formation can be illustrated simply by twisting the ends of a strap of a backpack.

Tailoring the properties of graphene, dichalcogenides and other 2D materials through electron irradiation: insight from DFT simulations and TEM experiments 1,2

Arkady V. Krasheninnikov, Hannu-Pekka Komsa, Natalia Berseneva, Simon Kurasch, Jani 1,4 1 3 4 2 Kotakoski, Ossi Lehtinen, Ute Kaiser, Jannik Meyer, Risto Nieminen 1

Department of Physics, University of Helsinki, P.O. Box 43, 00014 Helsinki, Finland Department of Applied Physics, Aalto University, P.O. Box 1100, 00076 Aalto, Finland Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, Ulm University, 89081 Ulm, Germany 4 Department of Physics, University of Vienna, Boltzmanngasse 5, 1090 Wien, Austria 2 3

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ABSTRACTS

akrashen@acclab.helsinki.fi

Recent experiments on electron and ion bombardment of 2D materials demonstrate that irradiation can have beneficial effects on such targets and that electron or ion beams can serve as tools to change the morphology and tailor mechanical, electronic and even magnetic properties of low-dimensional materials. In this presentation, our latest theoretical results on the response of graphene [1-2], h-BN [3] and several dichalcogenides (MoS2, MoSe2, WS2, etc) [4] to irradiation will be presented, combined with the experimental data obtained in collaboration with several groups. Transformation of graphene to an amorphous 2D sheet (Fig. 1) by the beam of energetic electrons will be discussed. It will be shown that bond rotations near vacancy-type defects (Fig.2) induced by energetic electrons are the main mechanism of the transformation. We will further study the stability of graphene ribbons under electron irradiation. It will be shown that the response of the ribbons to irradiation is not determined by the equilibrium energetics as assumed in previous experiments, but by kinetic effects associated with the dynamics of the edge atoms after impacts of energetic electrons, Fig.3. We will demonstrate an unexpectedly high stability of armchair edges, comparable to that of pristine graphene, and show that the electron energy should be below â&#x2C6;ź50 keV to minimize the knock-on damage at the edges. The electronic structure of graphene sheets with defects will be addressed as well, and possible avenues for tailoring the electronic structure of graphene by irradiation-induced defects [5] and impurities will be introduced. We will also discuss how electron irradiation and electron beam-assisted deposition can be used for engineering hybrid BN-C nanosystems by substituting B and N atoms with C atoms, Fig. 4. Using densityfunctional theory static and dynamic calculations, we show that the substitution process is governed not only by the response of such systems to irradiation, but also by the energetics of the atomic configurations, especially when the system is electrically charged. We suggest using spatially localized electron irradiation for making carbon islands and ribbons embedded into BN sheets.We further study the magnetic and electronic properties of such hybrid nanostructures and show that triangular carbon islands embedded into BN sheets possess magnetic moments, which can be switched on and off by electrically charging the structure. Finally, we present the results of firs-principles calculations [4] for displacement thresholds in various dichalcogenides. We will further touch upon the most frequent defect structures which appear in these materials under electron irradiation and compare the calculated defect configurations to those found in the transmission electron microscopy experiments [6]. Similar to h-BN, we explore how electron-beamassisted deposition can be used to change the atomic structure of dichalcogenides and tailor their electronic properties through doping.

References [1] [2] [3] [4] [5] [6]

J. Kotakoski, D. Santos-Cottin, and A. V. Krasheninnikov, ACS Nano 6 (2012) 671. J. Kotakoski, A. V. Krasheninnikov, U. Kaiser, and J.C. Meyer, Phys. Rev. Lett. 106 (2011) 105505. N. Berseneva, A. V. Krasheninnikov, and R.M. Nieminen, Phys. Rev. Lett. 107 (2011) 035501. H.-P. Komsa, J. Kotakoski, A. V. Krasheninnikov, to be published. F. Banhart, J. Kotakoski and A. V. Krasheninnikov, ACS Nano 5 (2011) 26. S. Kurasch, H.-P. Komsa, O. Lehtinen, A. V. Krasheninnikov, and U. Kaiser, to be published.

Figures

Figure 1: (a) Amorphous two-dimensional sp -bonded carbon membrane created by a high-dose exposure of graphene to 100 keV electron irradiation in an HRTEM. Scale bar is 1 nm. (b) Fourier transforms from HRTEM images of the initial graphene configuration and of the amorphous 2D carbon (c). Courtesy of J.C. Meyer and U. Kaiser.

Figure 2: Elementary defects and frequently observed defect transformations under irradiation. Atomic bonds are superimposed on the defected areas in the bottom row. Creation of the defects can be explained by atom ejection and reorganization of bonds via bond rotation. (a) Stone-Wales defect, (b) defect-free graphene, (c) single vacancy, (d) Divacancy, (e) 555-777 divacancy, (f) 5555-6-7777 divacancy. Scale bar 1 nm. Courtesy of J.C. Meyer and U. Kaiser.

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Figure 4: Schematic representation of the electron-beam-mediated substitutional doping of boron nitride monolayer. Hydrocarbon molecules decomposed by the beam provide carbon atoms which preferentially take place of boron atoms displaced by the beam or due to beam-induced substitution reaction. (a) Irradiation of the whole sample as done experimentally [X. Wei et al., ACS Nano 5, 29162922 (2011).] (b) Possible engineering of carbon island in BN matrix due to focused electron beam. (c) Experimental TEM image of a triangular hole formed in single BN sheet due to the electron beam [J. C. Meyer et al., Nano Lett. 9, 2683 (2009)].

ABSTRACTS

Figure 3: Different edge reconstructions as optimized with DFT (a) and their formation energies Ef and displacement thresholds Td (b). Displacement thresholds as calculated with both DFT and DFTB methods are presented.

Electronic properties of nitrogen doped graphene measured at the atomic scale

Jérôme Lagoute , Frédéric Joucken , Yann Tison , Jacques Dumont , Damien Cabosart , Bing 3 1 1 1 1 Zheng , Vincent Repain , Cyril Chacon , Yann Girard , Sylvie Rousset , Andrés Rafael Botello3 2 3 2 Méndez , Robert Sporken , Jean-Christophe Charlier and Luc Henrard 1

Laboratoire Matériaux et Phénomènes Quantiques, UMR7162, Université Paris Diderot Paris 7, Sorbonne Paris Cité, CNRS, UMR 7162 case courrier 7021, 75205 Paris 13, France 2 Research Center in Physics of Matter and Radiation (PMR), University of Namur (FUNDP), 61 Rue de Bruxelles, 5000 Namur, Belgium 3 Université Catholique de Louvain (UCL), Institute of Condensed Matter and Nanosciences (IMCN), 1/6 Place L. Pasteur, 1348 Louvain-la-Neuve, Belgium jerome.lagoute@univ-paris-diderot.fr

Chemical doping is a promising strategy for tailoring the electronic properties of graphene. The incorporation of nitrogen in the carbon lattice is a natural choice because of its suitable atomic radius and additional electron. The substitution of some carbon atoms by nitrogen is expected to give rise to a shift of the Dirac energy and an additional donor states. The local environment of the doping sites can also lead to various effects in the graphene electronic structure [1]. Experimentally, the link between the local atomic structure and electronic properties can be achieved using scanning tunneling microscopy (STM) and spectroscopy (STS) by combining atomic scale imaging with local spectroscopy. Using STM/STS operating in ultra high vacuum and at low temperature, we have investigated nitrogen doped graphene grown on SiC(000-1). Substitutional nitrogen has been found to be the most common configuration observed characterized by a specific triangular pattern similarly to the recently reported STM/STS study of N doped graphene prepared by chemical vapor deposition on a copper substrate [2]. The spatial distribution of the local density of states in high resolution images indicates a charge transfer between the nitrogen atom and its neighboring carbon atoms. Local spectroscopy reveals that doping induces a shift of the Dirac energy as expected for n-doping together with the formation of an additional localized state in the valence band. This finding is in agreement with Density Functional Theory (DFT) calculations. Beside the observation of single substitutional nitrogen atoms, various other atomic configurations have been observed revealing different electronic properties.

References

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[1] B. Zheng, P. Hermet, L Henrard, ACS Nano, 7 (2010) 4165 [2] L. Zhao et al., Science, 333 (2011) 999

Disordered Fermi Liquid in Epitaxial Graphene from Quantum Transport Measurements

Samuel Lara-Avila, Alexander Tzalenchuk, Sergey Kubatkin, Rositza Yakimova, T. J. B. M. Janssen, Karin Cedergren, Tobias Bergsten, and Vladimir Fal’ko Chalmers University of Technology, Kemivagen 9, Goteborg, Sweden samuel.lara@chalmers.se

Epitaxial graphene synthesized on the Si-terminated face of silicon carbide (SiC/G) has demonstrated the ability to supersede conventional semiconductors as the system of choice for fast analogue transistors, quantum metrology, and is also emerging as a suitable platform for such disruptive technologies as spintronics. In SiC/G, the two dimensional system is formed by a conducting graphene layer situated on top of a nonconducting buffer carbon layer, covalently bonded to SiC. The interplay between these two layers, unavailable in graphene flakes, graphene on the C face of SiC or conventional semiconductor-based 2D gases, makes SiC/G a system full of rich new physics. A detailed understanding of electron scattering and localization in this material is therefore important. We quantify the charge scattering in SiC/G by analyzing quantum corrections to conductivity from magnetotransport measurements at low temperatures and decoupling the two quantum transport phenomena contributing to effect: the Aronov-Altshuler electron-electron interaction (AA) and weaklocalization (WL). The analysis of the AA correction has confirmed that electrons in SiC/G display all the attributes of a disordered Fermi liquid and that the electron-electron interaction is responsible for dephasing in this system; from the analysis of WL has extract the characteristic times of symmetrybreaking disorder and intervalley scattering, finding a characteristic phase relaxation time of electrons of about 50 ps, which we attribute to the presence of local magnetic moments of defects in or under graphene. Based on this, we conclude that spin memory of electrons in a field effect transistor based on epitaxial graphene with n~1011 cm2 can exceed a micrometer scale, which proves the suitability of this system for applications in spintronics

References

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ABSTRACTS

[1] S. Lara-Avila, A. Tzalenchuk, S. Kubatkin, R. Yakimova, T. J. B. M. Janssen, K. Cedergren, T. Bergsten, and V. Fal’ko, Phys. Rev. Lett. 107, (2011), 166602.

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Figure 1: Magnetotransport measurements in monolayer SiC/G. (a) Temperature dependence of the characteristic scattering lengths and (b) decoherence rate for samples S1 (open markers) and S2 (solid markers). (c) Half-integer QHE proving the monolayer nature of SiC/G. Inset: Micrograph of one of the devices. (d) Weak localization peak at different temperatures.

Tailoring the atomic structure and electronic properties of graphene/metal interfaces by intercalation

Philipp Leicht , Konstantin Krausert , Lukas Zielke , Muriel Sicot , Florian Mittendorfer , 2 2 3 3 Andreas Garhofer , Josef Redinger , Daniela Pacilé , Marco Papagno , Polina Makarovna 3 3 3 4 1 Sheverdyaeva , Paolo Moras , Carlo Carbone , Yuriy S. Dedkov and Mikhail Fonin 1

Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany Institute of Applied Physics, TU Vienna, and Center for Computational Materials Science, Gusshausstrasse 25/134, A-1040 Wien, Austria 3 Instituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste, Italy 4 SPECS Surface Nano Analysis GmbH, 13355 Berlin, Germany 2

philipp.leicht@uni-konstanz.de

The interface between graphene and the substrate plays a vital role for graphene based applications. It influences the electronic properties concerning the position and form of the Dirac cone, furthermore spinfiltering capabilities are predicted for magnetic substrates [1]. Apart from direct growth of graphene on a small number of substrates, a variety of metals can be intercalated between graphene and the substrate interface [2,3] and allow for the production of graphene on a large number of materials. In this work, we present the investigation of Ni intercalation underneath graphene on Ir(111) and Rh(111). The atomic structure and electronic properties were investigated for samples with intercalated Ni ranging from a submonolayer to few monolayers. For Ni intercalation underneath graphene/Ir(111), scanning tunneling microscopy shows large monolayer thick areas of intercalated material accumulated at step edges. These areas show a strongly increased moiré corrugation as well as a decreased average distance of graphene from Ni/Ir(111) compared to Ir(111). The stronger corrugation in conjunction with considerable changes in the electronic structure measured by the photoemission spectroscopy suggests an increased bonding between graphene and Ni. The details of the atomic structure and electronic properties are discussed in the frame of recent DFT calculations of graphene/Ni/Ir(111).

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In both systems, we identify the intercalation paths to be via diffusion through either pre-existing defects in graphene, or metal-generated defects followed by the defect healing of the graphene lattice. For intercalation of Ni underneath graphene/Ir(111) large patches of material, often in the vicinity of step edges, are found and suggest long diffusion lengths of material at the interface of graphene and Ir(111) This is not the case for graphene/Ni/Rh(111), where the strongly bound bridge sites act as diffusion barriers. Similar diffusion barriers can be achieved after intercalation of more than one monolayer of Ni.

ABSTRACTS

For Ni intercalation underneath graphene/Rh(111) [2], we observe the formation of epitaxial nanoislands underneath graphene, which are scattered across the substrate terraces. The size and shape of nanoislands is strongly influenced by the local spatial variation of the graphene-Rh bonding strength involving size selection according to the moiré periodicity. Here, no considerable changes in bonding strength are observed as compared to graphene/Ni/Ir(111).

References [1] Karpan, V.; Giovannetti, G.; Khomyakov, P.; Talanana, M.; Starikov, A.; Zwierzycki, M.; van den Brink, J.; Brocks, G.; Kelly, P.; Phys. Rev. Lett. 99 (2007) 176602 [2] Sicot, M.; Leicht, P.; Zusan, A.; Bouvron, S.; Zander, O.; Weser, M.; Dedkov, Y. S.; Horn, K.; Fonin, M.; ACS Nano 6 (2012) 151 [3] Huang, L.; Pan, Y.; Pan, L.; Gao, M.; Xu, W.; Que, Y.; Zhou, H.; Wang, Y.; Du, S.; Gao, H.-J.; Appl. Phys. Lett. 99 (2011) 163107

Figures

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Figure 1: (a) STM topograph of intercalated Ni underneath graphene/Ir(111). Intercalated material shows increased moirĂŠ corrugation and accumulates at step edges. (b) STM topograph of intercalated Ni underneath graphene/Rh(111). Strongly bound areas of the graphene/Rh(111) moirĂŠ cell act as diffusion barriers for material, eventually forming intercalated islands with size-selection.

Simulation of electronic transport in defective graphene. From point defects to amorphous structures

1,2

3,4

1,5

1,2

Aurelien Lherbier , Stephan Roche , Simon M.-M. Dubois , Xavier Declerck , Oscar. A. 6 6 7 1,2 Restrepo , Arnaud Delcorte , Yann-Michel Niquet , and Jean-Christophe Charlier 1

Universite catholique de Louvain (UCL), Institute of Condensed Matter and Nanoscience (IMCN), NAPS, Chemin des etoiles 8, 1348 Louvain-la-Neuve, Belgium 2 European Theoretical Spectroscopy Facility (ETSF) 3 CIN2 (ICN-CSIC) and Universitat Autonoma de Barcelona (UAB), Catalan Institute of Nanotechnology, Campus UAB, 08193 Bellatera (Barcelona), Spain 4 Institucio Catalana de Recerca i Estudis Avancats (ICREA), 08070 Barcelona, Spain 5 University of Cambridge, Cavendish Laboratory, Theory of Condensed Matter group, JJ Thomson Avenue, Cambridge CB3 0HE, United-Kingdom 6 Universite catholique de Louvain (UCL), Institute of Condensed Matter and Nanoscience (IMCN), BSMA, Place Croix du Sud 1, 1348 Louvain-la-Neuve, Belgium 7 CEA-UJF, INAC, SP2M/L_Sim, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France aurelien.lherbier@uclouvain.be

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In this presentation, simulations of electronic transport in defective graphene membranes are exposed. Employing tight-binding models validated by ab initio calculations, and using a real-space order-N KuboGreenwood transport method [1-2], the effect of structural defects disrupting the ideal honeycomb lattice is theoretically investigated. The case of various concentrations of â&#x20AC;&#x153;point defectsâ&#x20AC;? or single structural defects such as vacancies and Stone-Wales defects is first studied (Fig.1). Then, electronic and transport properties in the presence of a mixture of different structural defects is examined. Finally, using molecular dynamics simulations, highly defective graphene membranes presenting domains of amorphous graphene structure [3-5] are created (Fig.2), and their transport properties are carefully inspected. Structural defects are found to induce strong resonant scattering states at different energies depending on the nature and the concentration of defects [6-8]. These induced resonant scattering states can yield to extremely short mean free paths and low mobilities. At low temperatures, they also lead to an enhanced contribution of quantum interferences driving to localization phenomena in the quantum transport regime. In case of highly defective graphene membrane, the amorphization of the structure changes the system into a strong two-dimensional Anderson insulator material [9], which could be experimentally confirmed by the observation of a variable range hopping transport behavior at low temperatures.

ABSTRACTS

Graphene, a one atom-thick membrane, has sparked out intense research activities from both experimental and theoretical sides since almost a decade now. The striking properties of graphene in various fields, such as mechanical, thermal, or electronic transport properties, are intrinsically related to its two-dimensional aspect and to its honeycomb lattice structure yielding both to the peculiar electronics of Dirac Fermions. From the electronic transport point of view, clean graphene samples exhibit particularly long coherence length and high electronic mobility both interesting for devices applications in nanoelecronics. Graphene provide simultaneously is genuine playground for fundamental researches such as exploration of Anderson (anti-)localization phenomena in real two-dimensional systems.

References [1] [2] [3] [4] [5] [6] [7] [8] [9]

S. Roche, D. Mayou, Phys. Rev. Lett. 79 (1997) 2518 A. Lherbier, X. Blase, Y.M. Niquet, F. Triozon, S. Roche, Phys. Rev. Lett 101 (2008) 036808 J. Kotakoski, A.V. Krasheninnikov, U. Kaiser, J.C. Meyer, Phys. Rev. Lett 106 (2011) 105505 V. Kapko, D.A. Drabold, M.F. Thorpe, Phys. Status Solidi B 247 (2010) 1197 E. Holmstrรถm, J. Fransson, O. Eriksson, R. Lizรกrraga, B. Sanyal, S. Bhandary, M.I. Katsnelson, Phys. Rev. B 84 (2011) 205414 T.O. Wehling, S. Yuan, A.I. Lichtenstein, A.K. Geim, M.I. Katsnelson, Phys. Rev. Lett. 105 (2010) 056802 Y.V. Skrypnyk, V.M. Loktev, Phys. Rev. B 82 (2010) 085436 A. Lherbier, S.M.-M. Dubois, X. Declerck, S. Roche, Y.M. Niquet, J.-C. Charlier, Phys. Rev. Lett. 106 (2011) 046803 A. Lherbier, S. Roche, O.A. Restrepo, Y.M. Niquet, A. Delcorte, J.-C. Charlier, submitted for publication (2012).

Figures

Figure 1: Three structural defects in graphene: (a) Stone-Wales, (b) Divacancy 585, and (c) Divacancy 555-777

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ABSTRACTS

Figure 2: Highly defective graphene (HDG) membrane: (a) Randomized graphene sample, (b) Structurally optimized model of HDG, (c) short list of frequently observed structural defects.

Cheap competitors of graphene -the actual use of carbon black and carbon fibres in the automotive and consumer industry

Renato Liardo Volvo Group Trucks Technology â&#x20AC;&#x201C; Advanced Technology & Research; Materials Technology 402 Av Charles de Gaulle, API: VNX AB1 1 02 - Gare 28, 69635, VĂŠnissieux - France renato.liardo@volvo.com www.volvogroup.com

Carbon black is one of the oldest products known. Its manufacturing process has seen improvements over the centuries. For which applications is carbon black used? The main characteristics that CB can provide are: colour, gloss, UV protection, fade resistance, heat protection, reinforcement, rheology control, electrical conductivity, thermal conductivity, reducing agent. Markets for the carbon black are mainly: rubbers, plastics, coatings, adhesives and sealants, printing inks, toners in industries as automotive, aerospace, marine, construction, packaging, electronics, cables for power transport and telecommunication, pipes for transport of water or gas, fibres for clothing and carpets. Carbon fibres were developed at the end of the 1950â&#x20AC;&#x2122;s, and today are very popular. Their atomic structure is similar to that of graphite. Why do we add carbon fibres to an application? To provide lightweight, high stiffness, high tensile strength, high fatigue resistance, high temperature resistance, low thermal expansion, high chemical inertness, low abrasion, good vibration damping, electrical conductivity, biological inertness, x-ray permeability, self-lubrication. Markets for the carbon fibres are mainly: aerospace, road and marine transports, sporting goods, missiles, aircraft brakes, loudspeakers for Hi-fi, medical prostheses, surgery and x-ray equipment, implants, tendon/ligament repair, textile machinery, chemical industry, nuclear field.

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This talk will give a "broad view" on the actual uses and issues on what can be considered as ready commercial alternative materials to graphene: carbon black and carbon fibres.

In Situ Real-Time Monitoring of interfacial Chemical-Electrical-Optical Phenomena in CVD-Graphene/Metal Hybrids 1

Maria Losurdo , Maria M. Giangregorio , Wenyuan Jiao , Evonne Yi , Tong-Ho Kim , 3 2 1 Iris Bergmair , April Brown and Giovanni Bruno 1

Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4, 70126 Bari, Italy Electrical Computer Engineering Department, Duke University, 27708 Durham, North Carolina, US 3 Instituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste, Italy 4 Profactor GmbH, Im Stadtgut A2 | 4407 Steyr-Gleink | Austria maria.losurdo@ba.imip.cnr.it

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As engineering applications of graphene attract increasing interest, we need in situ methods enabling realtime control of graphene growth in order to control its thickness and to tailor properties, as well as enhancing understanding interfacial phenomena involving graphene interactions with metals in hybrid devices. Among various synthesis approaches, chemical vapor deposition (CVD) has emerged as a reliable technological process for fabricating large area graphene. The scope of this contribution is to highlight experimental achievements obtained using real-time optical metrology with spectroscopic ellipsometry on the CVD growth of graphene, and its interactions with metals. Specifically, we show â&#x20AC;˘ Improvements in the properties of graphene achieved by optimizing CVD growth and establishing correlations between process kinetics and thickness. We have (i) demonstrated a real-time optical probing method to monitor and relate all steps involved in graphene growth by CVD (using CH4-H2) with its final thickness and quality; (ii) demonstrated a novel improved low-temperature H2 plasma process for the cleaning and crystallization of the metal catalysts Ni and Cu, to improve substrate quality and reduce the impact of grain boundaries effects on graphene properties; (iii) characterized carbon diffusion kinetics when CH4 in injected into the CVD system and demonstrated control of graphene thickness [Figure 1]; (iv) measured and articulated the impact of the H2/CH4 ratio on CVD growth kinetics, graphene thickness and structural and optical properties [Figure 2]. The quality of the synthesized graphene is revealed by the perfect Lorentzian fit of the 2D peak at 2702 cm-1 with FWHM of approximately 33 cm-1. The absence of the Raman D peak at 1350 cm-1 indicates the absence of defects. Furthermore, microscopy indicates a good uniform thickness coverage, which from the I2D/IG Raman ratio, can be estimated to be from a monolayer to a 3-layers depending on growth conditions. â&#x20AC;˘ New opportunities for the facile design of plasmonic graphene/metal systems based on charge transfer. Charge transfer is crucial for characterizing metal/graphene interfaces and understanding a wide range of light-matter interactions and devices, such as plasmon-coupling across the materials components and plasmon-electron coupling in plasmaron-based devices. In addition, metals on graphene allow the controlled modification of the Fermi energy across the system, enabling effective graphene doping. Here, we provide for the first time the direct evidence of the tunability of the plasmon resonance of graphene coupled to plasmonic metal nanoparticles (NPs) [Figure 3]. The novel Ga NP/graphene system is an excellent model of a weakly-bound metal-graphene interface thus preserving graphene electronic structure. Unlike transition metals, Ga (gallium) is a sp metal yielding a predominantly ionic interaction with graphene, i.e. without strong hybridization between the pz orbitals of graphene and the valence electrons of Ga, and with a weak bonding charge yielding minimal distortion of the graphene lattice. Furthermore, graphene/Ga NPs offer a plasmonic system with broad surface resonance tunability, from the UV to the near-IR range, enabling coupling of the plasmon resonance with graphene UV absorption at 4.6 eV and its intrinsic Ď&#x20AC; plasmon. The role of graphene in the charge transfer, between the metal NPs and the substrate, on the plasmon resonance

energy and amplitude is discussed also in comparison with other metals such as silver (Ag) that interacts electronically much more strongly with graphene • Improvements in graphene/Ag system stability. The interface chemistry and electronic phenomena underpinning the coupling of graphene with silver gratings and fishnet structures enable novel realizations of hybrid functional materials, which are oxidation resistant and possess stable plasmon resonances in the visible range. A chemical model based on the electron transfer from graphene to silver is articulated to rationalize the oxidation resistance behavior of silver/graphene structures and the new chemical/optical properties of the hybrid [Figure 4]. These results on graphene/metals have significant impact on a variety of fields, including optical metrology, SERS-based sensors, renewable energy, plasmonics, metamaterials, specifically through the development of novel graphene/silver composites. We acknowledge funding of the FP7 European project NIM-NIL (GA 228637) www.nimnil.org References [1] M. Losurdo et al. Phys. Chem. Chem. Phys., 13 (2011) 20836. [2] M. Losurdo et al. J. Phys. Chem. C. 115 (2011) 21804. [3] M. Losurdo et al. Small (2012).

Figures Figure 1: Correlation between real time monitoring of graphene CVD growth and final graphene quality. (a) Realtime evolution of extinction coefficient, <k>, monitored during annealing of the 300 nm Ni/300 nm SiO2/Si substrate in H2. (b) Corresponding AFM images recorded for the three Ni substrates annealed at different temperature. (c) Realtime <k> evolution during graphene growth on the three characteristics Ni substrates. (d) Raman 100 μmx100 μm maps of the I2D/IG intensity ratio for FLG samples corresponding to the various kinetics and (e) Raman spectra acquired in characteristic points indicated by the yellow dot. Blue region corresponds to monolayer-graphene; green region to 2-3 layers graphene and light green to >3 layers graphene [1].

Figure 4: Graphene-Silver Metamaterials. AFM and SEM views of a graphene-silver metamaterials in the visible. XPS shows that advantage of graphene is preserving the metal Ag structure after 1 month of air exposure.

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Figure 3: Plasmon Resonance for Ga NPs/graphene plasmonic hybrids. Real-time evolution of the extinction coefficient spectra of the plasmon resonance for plasmonic Ga nanoparticles/graphene [3].

ABSTRACTS

Figure 2: Impact of CH4-H2 ratio on graphene growth on Ni and Cu. (a) Real-time evolution of <ε1> monitored during graphene growth on Cu at various CH4/H2 ratios. The Raman spectra for 2 samples are also shown with explicit I2D/IG ratio, indicative of the graphene thickness, and IG/ID ratio, indicative of defects. (b) Typical Raman spectrum for graphene grown on Ni at CH4:H2=100:10; no D-peak is observed; the dependence of the 2D peak intensity and FWHM, as a function of increasing H2 for graphene on Ni is also shown [2].

Collective properties of Dirac electrons in graphene 1,2

Yu. E. Lozovik 1 2

Institute of Spectroscopy, 142190 Troitsk, Moscow region, Russia Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Moscow region,Russia

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lozovik@isan.troitsk.ru

Graphene, a two-dimensional form of carbon with honeycomb lattice, has attracted a lot of attention of condensed-matter community due to its unique properties [1-3]. In the present talk we consider new phases and collective properties of graphene structures. We discuss also various applications of graphene as a constituents for for the elements of plasmonics, nanophotonics and photonic crystals. Electron-hole pairing caused by Coulomb interaction in the system of independently gated graphene layers separated by dielectric barrier is discussed. The theory of Cooper pairing of massless spatially separated Dirac electrons and holes at strong coupling in graphene bilayer is presented. Similarity and distinction from phenomena in semiconductor coupled quantum wells (see [4] and cit.lit.) will be discussed. The essential distinctions are due to Berry phase of electronic wave functions and different screening properties. Localized electron-hole pairs (at zero magnetic fields) are absent in graphene, thus the behavior of the system versus coupling strength is cardinally different from usual BCS-BEC crossover. Various factors, leading to enlargement of the critical temperature at strong coupling beyond Bardeen-Cooper-Schrieffer model predictions, are considered. These important factors are multi-band character of the pairing, dynamical and correlation effects [5-8]. The collective properties of different types of quasiparticles in graphene is considered - 2D spatially indirect magnetoexcitons in two-layer graphene, magnetoexcitonic polaritons (magnetopolaritons) in a graphene layer embedded in an optical microcavity in a strong magnetic field (see also [4, 9-13] and cit.lit.). We predict Bose-Einstein condensation (BEC), Kosterlitz-Thouless transition and superfluidity of indirect magnetoexcitons and magnetoexcitonic polaritons in a strong magnetic field. Strongly correlated phases of of magnetoexcitons in bilayer graphene is predicted. The e-h condensation in coupled graphene sheets can be observed through essential rise of e-h drag, Josephson-like phenomena etc. The quasi-equilibrium system of magnetoexciton polaritons, quantum superposition of optical microcavity photons and magnetoexcitons in embedded graphene is considered. Fixation of relative phase of two order parameters corresponding to exciton and cavity photons is analyzed. The transition temperature to superfluid state of cavity magnetopolaritons was found as the function of exciton-photon detuning and Rabi splitting. Excitations in the system are discussed. Magnetopolaritons, quantum superposition of optical microcavity photons and magnetoexcitons in graphene (embedded in optical microcavity) are studied. Coherent state of magnetopolariton system is considered . Different 2D traps for cavity polaritons are analyzed(see also [4] and cit.lit.). The systems considered give the possibility to create nondissipative nanoelements for information transfer operating even at room temperatures. We consider disorder effect on electron–hole pairing in the system. The influence of charged impurities on temperature of phase transition is studied. The quantum hydrodynamics of the system is considered and phase stiffness of electron–hole condensate and temperature of Berezinskii–Kosterlitz–Thouless transition to the superfluid state are calculated. Dependence of critical temperate on mismatch of Fermi lines of e and h and value of triagonal warping of their spectrum is obtained. We predict appearance of the ground state with finite value of Cooper pair momentum at mismatch of the Fermi lines above the critical value. We show that spatial structure of the order parameter in this state can be reconstructed from the dependence of tunnel current between the layers on value and direction of parallel magnetic field. Collective properties and coherent phases of graphene structures in high magnetic fields are discussed. Instabilities in the system, particularly, coherent state formation originated from composite fermions pairing

are analyzed. Drag effects in graphene structures are considered. The similarity and dissimilarity in properties of Dirac electron system, particularly their collective properties in graphene vs. 3D topological insulators are discussed. The method of calculations of nanoelements based on graphene by generalized density functional approach for system with “ultrarelativistic” electronic spectra are developed. The electromagnetic response of a composite medium consisting of monolayer graphene particularly graphene based photonic crystals are discussed (see also [14]). The advantages of the graphene-based photonic crystal are discussed. Plasma oscillations, plasmon polaritons and instabilities in graphene , graphene array and in surface of 3D topological insulator are discussed. Phonons and possible superconductivity in strongly doped graphene are analyzed. Possible NEMS based on graphene are analyzed (see also [15-18]). Plasmon polaritons in a monolayer and bilayer doped graphene embedded in optical microcavity are discussed. The dispersion law for lower and upper cavity plasmon polaritons was obtained. Peculiarities of Rabi splitting for the system are analyzed; particularly, role of Dirac-like spinor (envelope) wave functions in graphene and corresponding angle factors were considered. Typical Rabi frequencies and frequencies of polaritons near polariton gap were estimated. The condition of existence of the lower pair of polaritons in the bilayer graphene system (corresponding to the antiphase plasmon mode) was obtained. The collective excitations in a helical electron liquid on a surface of three-dimensional topological insulator were studied. Analogies with Dirac electron gas in graphene are discussed. The plasmon polaritons in the system can be used for high-speed information transfer in the THz region. The influence of the optical contrast between the two media, located on opposite sides of graphene on the behavior of electromagnetic waves with TE and TM polarization is studied. It occurs that TE-polarized waves becomes leaky due to the increase of the optical contrast. In the case under consideration TE-mode frequency lies only in the window determined by the contrast. Analytical expressions describing the frequency range and extent of leakage depending on the contrast are obtained. The different characteristics of leaky modes - the wave vector, phase and group velocities, the characteristic length of leakage - are studied in detail. The sensitivity of TE-modes to changes in contrast is estimated. Near the frequency where the imaginary part of the conductivity of graphene vanishes, the very high sensitivity and very low detection limit are found. The effect considered can be used for design of highly sensitive optical sensors based on graphene. It is expected that they can essentially outperform modern plasmon resonance sensors. The influence of metamaterial substrate on the TE-polarized electromagnetic waves in graphene is studied.

[6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

K. Geim, K. S. Novoselov, Nature Materials 6, 183 (2007). M.Katsnelson , Materials Today 10, 20 (2007). Castro Neto AH, Guinea F, Peres NMR, Novoselov KS, Geim AK,Rev. Mod. Phys. 81 109 (2009) Yu.E.Lozovik, Physics-Uspekhi, 52, 286 (2009). Yu.E. Lozovik, A.A. Sokolik, JETP Lett., 87, 55(2008); Physics-Uspekhi, 51, No.7, pp. 727-748 (2008). Phys. Lett. A 374, 326(2009). Eur. Phys. J. B 73, 195 (2010); Phys. Lett. A 374, 2785 (2010). Yu.E. Lozovik, S.Ogarkov, A.A.Sokolik, Philosophical Transactions of the Royal Society A, Special Issue on “Graphene” 368, 5417-5429 (2010). Efimkin D. K, Lozovik Yu. E., J. Exp.Theor.Phys.113, 880 (2011). Efimkin D. K., Kulbachinskii V. A., Lozovik Yu. E.,JETP Lett., 93, 219 (2011). O. L. Berman, Yu. E. Lozovik, G. Gumbs, Phys. Rev. B 77, 155433 (2008); Phys.Rev.,B 78, 085401(2008). O. L. Berman, R. Ya. Kezerashvili, and Yu. E. Lozovik, Phys. Rev. B 78, 035135 (2008); Phys. Rev. B 80, 115302 (2009); Nanotechnology 21, 134019 (2010). Yu.E. Lozovik, A.A. Sokolik, M. Willander, Physica Status Solidi A 206, 927-930 (2009). O. L. Berman, R.Ya. Kezerashvili, Yu.E. Lozovik, and D.W. Snoke, Philosophical Transactions of the Royal Society A, Special Issue on “Graphene” 368, 5459–5482 (2010). O.L. Berman, R.Ya. Kezerashvili, Yu.E. Lozovik , D.W. Snoke, R. Balili , B. Nelsen, L. Pfeiffer, K. West, Superlattices and Microstructures 49 , No.3, 331–336 (2011). O.L. Berman, V.S. Boyko, R.Ya. Kezerashvili, A.A.Kolesnikov, Yu.E.Lozovik, Phys. Lett. A374, 3681-3684(2010). I.V. Lebedeva, A.A. Knizhnik, A.M. Popov, O.V. Ershova, Yu.E. Lozovik, B.V. Potapkin, Phys. Rev. B 82(15) 155460 (2010). I.V. Lebedeva, A.A. Knizhnik, A.M. Popov, Yu.E. Lozovik, B.V.Potapkin, Phys. Chem. Chem. Phys 13, 5687-5695 (2011). A.M. Popov, I. V. Lebedeva, A.A. Knizhnik, Yu.E. Lozovik, B.V. Potapkin, Phys.Rev.B 84, 045404 (2011). A.M. Popov, I.V. Lebedeva, A.A. Knizhnik, Yu.E. Lozovik, B.V. Potapkin, Phys.Rev.,B 84, 245437 (2011).

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[1] [2] [3] [4] [5]

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References

Near term commercial opportunities and applications of graphene

Christy Martin Vorbeck Materials Corp, 8306 Patuxent Range Rd, Unit 105, Jessup, MD 20794, USA christy.martin@vorbeck.com

Vorbeck Materials Corp. is a technology company established in 2006 to manufacture and develop applications using Vor-x™, Vorbeck's patented graphene material developed at Princeton University. Vorbeck launched the world’s first commercial graphene product in 2009 with the introduction of Vorink™, a graphene-based conductive ink. Vor-ink™ formulations harness the exceptional conductivity of graphene into ultra-flexible and robust inks and coatings for the printed electronics market. Designed for operation on standard graphic printing presses without the need for specialized equipment, Vor-ink™ has successfully run on commercial presses at speeds up to 150 m/min. Vor-ink™ is currently being used in a range of consumer applications from printed circuits to sensors and goods using Vor-ink™ circuits are on the shelves in major retailers today. In conjunction with the Pacific Northwest National Labs (PNNL) and Princeton University, Vorbeck has also developed Vor-charge™, a fully formulated anode composite next-generation battery electrode material, which entered beta testing with commercial partners in 2010. The team is also developing next generation lithium batteries, including lithium-sulfur and lithium-air systems and is working to rapidly bring this new technology to market. Vorbeck is partnering with Hardwire LLC to integrate the new batteries into hybrid military vehicles and is collaborating with companies to incorporate the new technology in toys, tools, and commercial vehicles.

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We will discuss the latest technical advancements in our Vor-ink™ materials and their role in enabling (through improved performance, reduced cost, and simplified processing) item-level applications to highvolume consumer goods. Updates on energy storage products and composite materials will also be discussed.

Graphene Electrodes For Nano-LEDs

Javier Martinez, A. Bosca, A. Bengoenchea-Encabo, S. Albert, M. A. Sanchez-Garcia, E. Calleja, F. Calle ISOM Instituto de Sistemas Optoelectrónicos y Microtecnología, E.T.S.I.Telecomunicación, Universidad Politécnica de Madrid, 28040 Madrid, Spain javier.martinez@isom.upm.es

III- Nitride nanocolumns (III-N NCs) are the subject of intense research since the past decade because of their unique properties and potential electronic and optoelectronic applications. NCs are usually grown on Si(111), Si (100), SiC, and sapphire substrates by a self-assembly process using plasma-assisted molecular beam epitaxy [1-3]. Unlike continuous layers, NCs accommodate the lattice-mismatch with the substrate through a network of misfit dislocations localized at the hetero-interface. Therefore, they grow fully relaxed and free of extended defects such as basal plane stacking faults or threading dislocations. This fact makes III-N NCs excellent candidates to develop arrays of highly efficient nanolight-emitters in the infrared-visible-ultraviolet range. Finally, the efficiency of a nanolight emitter will be increased if the NCs are aligned in a periodic pattern. Normally the transparent conducting electrode used for the light emitting diodes (LEDs) is the indium tin oxide (ITO), but this material has a high cost and is instable in the presence of acids or bases and has poor transparency in the blue and near-infrared light ranges [4]. Furthermore the need for a substitute for ITO is ever increasing due to the limited availability of indium on earth [5]. Graphene is the ideal candidate in order to replace the ITO due to its excellent electrical, optical and mechanical properties. So in this work we used graphene as a transparent electrode to fabricate the nanoLEDs.

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In conclusion, we propose the use of a graphene layer as a transparent electrode for GaN nanoLEDs. The electrical conductivity is higher than with ITO and its flexibility makes it the best material for contacting all the nanocolumns.

ABSTRACTS

In our approach, we decided to use a focus ion beam system (ionLine from Raith, Germany) in order to create the nanostructures (see Fig. 1). This technique will pattern our substrate in only one step and with high precision in the periodicity due to the laser interferometric stage. The sample used was a 2 inch wafer of GaN over a sapphire substrate (Lumilog, France). A thin layer of 7 nm of Ti was deposit on top. The metal layer was patterning by the ionLine with holes of 100 nm and a pitch of 250 nm in writing fields of 50 μm. A matrix of 64 elements was fabricated covering an area of 400 μm2. After this one step process, the sample was inserted inside a plasma assisted MBE in order to grow the NCs. With different conditions one can create NCs with diverse doping (n or p) creating nanoLEDs. These devices are coated with a layer of SiO2 as isolator. Finally, on top we deposit a layer of graphene as transparent electrode. The electrical characterization of the devices was made with AFM and with a probe station with a semiconductor analyzer. In figure 2, one can observe different steps in the fabrication of the nanoLED: AFM image of the nanoholes created by the ion beam system, SEM image of the nanoLEDs grow in the MBE system and I/V curve obtained in this device.

References

[1] M. Yoshizawa, A. Kikuchi, M. Mori, N. Fujita, K. Kishino, Jpn. J. Appl. Phys. 36 (1997) L459. [2] M. A. Sanchez-Garcia, E. Calleja, E. Monroy, F. J. Sanchez, F. Calle, E. Mu単oz , R. Beresford, J. Cryst. Growth 183 (1998) 23. [3] L. Cerrutti, J. Ristic, S. Fernandez-Garrido, E. Calleja, A. Trampert, K. H. Ploog, S. Lazic, J. M. Calleja, Appl. Phys. Lett. 88 (2006) 213114. [4] G. Jo, M. Choe, C. Y. Cho, J. H. Kim, W. Park, S. Lee, W. K. Hong, T. W. Kim, S. J. Park, B. H. Hong, Y. H. Kahng, T. Lee, Nanotechnology 21 (2010) 175201. [5] H. Park, J. A. Rowehl, K. K. Kim, V. Bulovic, J. Kong, Nanotechnology 21 (2010) 505204.

Figures

Figure 1: Fabrication scheme of the GaN nanoLEDs. A Titanium thin metal layer is deposited along the wafer with an ebeam evaporator. In a second step, a metal layer is patterned with an ion beam equipment in order to create nano-holes arrays. In a third step, the sample in inserted in a MBE system and the nanoleds grow inside the patterned areas. Finally, is deposit a layer of SiO2 and on top a graphene layer as electrode.

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Figure.2: AFM image of the nano-patterned holes on the Ti metal layer.SEM image of the selective area growth of GaN NCs by PA-MBE. Electrical characterization of the nanoLEDs.

Large crystalline graphene oxide sheets from helical ribbon carbon nanofibres

C. Merino , P. Merino , H. Varela-Rizo , I. Rodriguez-Pastor , I. Martﾃｭn-Gullﾃｳn GRAnPH Nanotech 1 Grupo Antolin Ingenieria, SA. Ctra. Madrid 窶的rﾃｺn, km. 244.8, E09007 Burgos, Spain 2 Chemical Engineering Department, University of Alicante, 03080 Alicante, Spain

cesar.merino@granphnanotech.com

Among the different methods that are currently known to obtain graphene, the chemical methods through the intercalation compounds of acids or/and oxysalts yielding graphite oxide, seems to be, at the moment, the most promising technique to produce large quantities and thus supply the increasing demand on graphene products. Commonly, natural graphite is used as a raw material[1], The subsequent exfoliation of the intermediate graphite oxide produces, more precisely, graphene oxide, by definition single layer or up 10 stacking layers. As graphite is composed by hundreds or thousands of graphene layers, complete separation of all the layers is difficult and therefore the yield in graphene oxide sheets becomes low. Other approaches have been use carbon nanotubes (CNT), which are also a graphitic material, with less number of graphene layers [2]. Considering these examples, we use helical ribbon carbon nanofibers (HR-CNF) to produce graphene oxide sheets. The HR-CNFs are CVD-produced by Grupo Antolin (Burgos, Spain) by the floating catalyst method at industrial scale, in a continuous process. Structurally, these filaments have a wide hollow core and a highly graphitic structure, which is formed by a ribbon rolled along the fiber axis developing a continuous spiral. This ribbon is composed of around 5 stacked graphene layers and this is the key point of our production method, the structure of the CNFs is rolled graphene that has to be unzipped. The production method consist of two steps, in the first step, the CNFs are unzipped by chemical oxidation with a modified Hummers reaction [3, 4], in the second step the layers of the obtained graphene oxide are even more separated and exfoliated by ultrasonication.

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This graphene oxide was introduced in an epoxy matrix [5]. The combination of O and N present groups in the structure of the graphene oxide resulted in impressive improvements in the fracture toughness and the fatigue life of the G-O/epoxy nanocomposites.

ABSTRACTS

Characterization of this material seems to disagree when analyzing the bulk and just one graphene oxide layer. X Ray Photoelectron Spectroscopy (XPS) shows a high content of oxygen, while electron energy loss spectroscopy (EELS) analysis performed in one layer shows a much less oxidized material. Interestingly, both analysis detect N in the structure, thus the graphene oxide sheets are presumably N-doped. The single layer of graphene oxide was also analyzed by Raman spectroscopy, so the contributions of the sp2 and sp3 C domains are certainly these corresponding to just one layer.

References [1] Stankovich S, Dikin DA, Piner RD, Kohlhaas KA, Kleinhammes A, Jia Y, Wu Y, Nguyen ST, Ruoff RS, Carbon, 7 (2007) 1558-65. [2] Kosynkin DV, Higginbotham AL, Sinitskii A, Lomeda JR, Dimiev A, Price BK, Tour JM, Nature, 7240 (2009) 872-76. [3] Hummers W, Offeman R, J Am Chem Soc,(1958) 1339. [4] Varela-rizo H, Rodriguez-pastor I, Merino C, Terrones M, Martin-gullon I, J Mater Res, 20 (2011) 2632-41 [5] Bortz DR, Heras EG, Martin-Gullon I, Macromolecules,(2011).

Figures

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Figure 1: TEM images of: A) HR-CNF; B) evidence of the spiral structure of the HR-CNFs with a scheme of the structure; C) single layer graphene oxide obtained from the HR-CNFs

Europium on graphene: phase coexistence of clusters and islands

2,3

Thomas Michely , Daniel F. Förster , Tim O. Wehling , Stefan Schumacher , Achim Rosch 1

II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany Institut für Theoretische Physik, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany Bremen Center for Computational Materials Science, Am Fallturm 1a, 28359 Bremen, Germany 4 Institut für Theoretische Physik, Universität zu Köln, Zülpicher Straße 77, 50937Köln, Germany 2 3

michely@ph2.uni-koeln.de

In recent years, it has become apparent that the properties of graphene, even if present in high structural quality, depend critically on its environment, e.g. on the type and distribution of chemical species adsorbed to graphene. This critical dependence of the graphene properties on the environment may also be turned into an advantage if new compound materials are constructed that bestow graphene with novel properties while keeping the desirable features of its electronic structure intact (e.g. its conical bands and the Dirac cone). As an example, it was proposed to bring the ferromagnetic insulator EuO into contact with graphene in order to induce a spin split Dirac cone with the resulting option for spin filtering in graphene [1]. Due to the large magnetic moment of 7μB of the Eu 4f-shell, also metallic Eu is a material with the potential to bestow graphene with magnetic properties. As a prerequisite for future work in this direction, it is necessary to understand in detail the adsorption and growth of Eu on graphene. Moreover, we believe that a systematic study of Eu adsorption and growth as a function of coverage and temperature under controlled ultra high vacuum conditions offers insight into fundamental aspects of the interaction of graphene with an entire class of materials.

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Most remarkably, at 300K in an intermediate coverage range a phase of uniformly distributed Eu clusters (size 10–20 atoms) coexists in two-dimensional equilibrium with large Eu-islands in a ( 3 x 3)R30° structure. We argue that the formation of the cluster phase is driven by the interplay of three effects: Firstly, the metallic Eu–Eu binding leads to the local stability of ( 3 x 3)R30° structures. Secondly, electrons lower their kinetic energy by leaving the Eu clusters, thereby doping graphene. Thirdly, the Coulomb energy penalty associated with the charge transfer from Eu to graphene is strongly reduced for smaller clusters.

ABSTRACTS

In this work [2], we investigate the adsorption and equilibrium surface phases of Eu on graphene on Ir(111) in the temperature range from 35 to 400K and for coverages ranging from a small fraction of a saturated monolayer to the second layer. We combine temperature-dependent Eu growth and annealing experiments, scanning tunnelling microscopy, work function measurements by I(z) scanning tunneling spectroscopy, low-energy electron diffraction, density functional theory calculations including 4f-shell Coulomb interactions and qualitative modelling of electronic interactions in order to gain an understanding of the Eu/graphene adsorbate system.

References [1] H. Haugen, D. Huertas-Hernando and A. Brataas, Phys. Rev. B 77 (2008) 115406. [2] D.F. Fรถrster, T.O. Wehling, S. Schumacher, A. Rosch and T. Michely, New J. Phys., in print (2012).

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Figure 1: Scanning tunneling microscopy topographs taken at 35 K after Eu deposition at 300K on a perfect graphene layer on Ir(111). Left: 3.3% ML Eu coverage. Right: 12% ML Eu coverage. 100% ML corresponds to one adsorbed atom per graphene unit cell. Image size 320 nm x 320 nm. Inset size 40 nm x 40 nm.

Graphene Based Terahertz Emitter

Sergey Mikhailov Institute of Physics, University of Augsburg, UniversitĂ¤tsstr. 1, D-86135, Augsburg, Germany sergey.mikhailov@physik.uni-augsburg.de

A specific design of a voltage tunable graphene based emitter and amplifier of electromagnetic radiation is developed [1]. The proposed device consists of a few layers of graphene and hexagonal boron nitride (BN) and is specifically structured in order to fulfill the threshold conditions for radiation and to optimize the efficiency of radiation. A detailed theory of the device is developed. The influence of different physical parameters (geometrical dimensions of the structure, electron/hole density, temperature, mean free path, voltage biases) on the device operation is analyzed and the optimal and realistic conditions of the device operation are found. It is shown that the proposed device is able to emit radiation in several frequency bands from ~0.1 up to ~30 THz. The estimated emitted power is of order of 0.5 W/cm2 and the estimated efficiency (the ratio of the emitted power to the heating power) is about 1%. The operating temperature of the emitter can be close to room temperature, the heating of the device does not exceed several Kelvin under realistic experimental conditions due to the very large surface-to-volume ratio in two-dimensional graphene and to the high thermal conductivity of the BN or silicon substrate which can be used. A slightly modified version of the basic structure can serve as an amplifier of a low frequency signal or as a terahertz transistor combined with a distributed plane antenna. Other opportunities of using graphene for terahertz science and technology will also be discussed. The theoretically predicted [2,3] and later experimentally observed [4,5] nonlinear phenomena in graphene, such as the frequency multiplication and mixing, will be overviewed. A new predicted effect of a giant enhancement of higher harmonics due to plasma resonances will be presented [6].

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[1] S.A.Mikhailov, European patent application â&#x20AC;&#x153;Graphene-based nanodevices for terahertz electronicsâ&#x20AC;? filed in December 2011. [2] S.A.Mikhailov, Europhys. Lett. 79, 27002 (2007). [3] S.A.Mikhailov and K.Ziegler, J. Phys. Condens. Matter 20, 384204 (2008). [4] E.Hendry, P.J.Hale, J.Moger, A.K.Savchenko and S.A.Mikhailov, Phys. Rev. Lett. 105, 097401 (2010). [5] M.Dragoman, D.Neculoiu, G.Deligeorgis, G.Konstantinidis, D.Dragoman, A.Cismaru, A.A.Muller and R.Plana, Appl. Phys. Lett. 97, 093101 (2010). [6] S.A.Mikhailov, Phys. Rev. B 84, 045432 (2011).

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References

Optical Excitations and Nanoplasmonics in Graphene Flakes and Ribbons

1,2

Elisa Molinari , Caterina Cocchi , Deborah Prezzi , Alice Ruini , Marilia J. Caldas and 2 Stefano Corni 1 2 3

Physics Dept., University of Modena and Reggio Emilia, Modena, Italy S3 Center - CNR Nanoscience Institute, Modena, Italy Instituto de Fisica, Universidade de São Paulo, SP, Brazil elisa.molinari@unimore.it

The fabrication of nanoscale graphene ribbons of finite length is now reaching atomic scale accuracy and extreme edge control [1], and further geometries [2] and substrates are being explored experimentally. Here we present a theoretical investigation of the optical excitations of elongated nanoflakes and ribbons. We focus both on intrinsic field enhancement effects and on the modification of the optical properties by means of edge modulation, functionalization and distortions. We employ either quantum chemistry semiempirical approaches [3-4] or ab-initio techniques [5], depending on the system type. We find that the optical spectra of elongated graphene flakes are dominated at low energy by excitations with strong intensity, comprised of characteristic coherent combinations of a few single-particle transitions with comparable weight. They give rise to stationary collective oscillations of the photoexcited carrier density extending throughout the flake, and to a strong dipole and field enhancement. This behavior is robust with respect to width and length variations, thus ensuring tunability in a large frequency range. The implications for nanoantenna and other nanoplasmonic applications are discussed for realistic geometries down to the nm and sub-nm, where atomistic and quantum mechanical effects are found to play a key role. Our work shows that width modulation and edge functionalization [3-4] can be exploited to design both type-I (straddling) and type-II (staggered) all-graphene nano-junctions. In the first case, we find that minimal width-modulations are sufficient to obtain confinement of both electrons and holes, thus forming optically active quantum dots with unique properties [5]. In the second case, we demonstrate that electron affinities and ionization potentials of GNFs can be tuned to form both types of nanojunction [3]. At variance to type-I, type-II GNJs can display indirect excitations with electron and hole densities localized on opposite sides [4]. The effect of functionalization-induced distortions is also discussed.

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References [1] [2] [3] [4] [5]

J. Cai et al,. Nature 466, 470–473 (2010) S. Blankenburg et al., ACS Nano asap article, DOI: 10.1021/nn203129a. C. Cocchi et al,. J. Phys. Chem. C 115, 2969-2973 (2011). C. Cocchi et al. J. Phys. Chem. Lett. 2, 1315–1319 (2011). D. Prezzi et al,. Phys. Rev. B 84, 041401 (2011).

Folds and buckles at the nanoscale: experimental and theoretical investigation of the bending properties of graphene membranes

Vittorio Morandi , Luca Ortolani , Emiliano Cadelano , Giulio Paolo Veronese , Cristian Degli 1 4 2,3 Esposti Boschi , Etienne Snoeck and Luciano Colombo 1

CNR IMM-Bologna, Via Gobetti, 101, 40129 Bologna, Italy CNR IOM-Cagliari, Cittadella Universitaria, 09042 Monserrato, Italy University of Cagliari, Physics Department, Cittadella Universitaria, 09042 Monserrato, Italy 4 CEMES-CNRS, 29 rue Jeanne Marvig, 31055 Toulouse, France. 2 3

morandi@bo.imm.cnr.it

While the unique elastic properties of monolayer graphene (under either stretching or bending loading conditions, as well as both in the linear and nonlinear regimes) have been extensively investigated [1-4], comparatively less knowledge has been developed so far on folded graphene ribbons. Nevertheless, it has been recently suggested that fold-induced curvature (occurring without in-plane strain) could possibly affect the local chemical reactivity [5], the mechanical properties [6] and the electron transport of graphene membranes [7]. This is indeed an intriguing perspective, since a proper engineering of the folding and/or bending could enable a materials-by-design approach where tailored ribbons are used as enhanced nano-resonators or nano-electro-mechanical devices. In this work we will review an ongoing effort to understand the combined folding and bending properties of graphene, where high-resolution transmission electron microscopy (HREM), continuum elasticity theory, and tight-binding atomistic simulations are concurrently combined to provide a complete nanoscale geometrical and physical picture. In particular, we will focus on the edge curvature and topography of folded graphene membranes, with different crystalline orientations. Figure 1 shows the equilibrium shape for a closed bi-layered edges graphene nanoribbon predicted by atomistic simulations. Theoretical predictions were validated by applying a novel experimental methodology for the transmission electron microscope, capable of recovering the 3D topography of the folded membrane. Figure 2-a shows the experimental HREM image of a folded monolayer. Apparent strains in the graphene lattice (Fig. 2-b) can be used to recover the 3D shape of the folded edge (Fig. 3-d), with sub-nanometre lateral resolution and height precision.

V. Pereira and A. Castro Neto. Phys. Rev. Lett. 103, 046801 (2009). E. Cadelano et al. Phys. Rev. Lett. 102, 235502 (2009). E. Cadelano et al. Phys. Rev. B 81, 144105 (2010). Kim et al. Phys. Rev. B 83, 245433 (2011). V. Tozzini and V. Pellegrini. C 115, 25523 (2011). Y. Zheng et al. Nanotechnology 22, 405701 (2011). E. Prada et al. Phys. Rev. Lett. 105, 106802 (2010).

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[1] [2] [3] [4] [5] [6] [7]

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References

Figures

Figure 1: Modeled closed bi-layer edge graphene nanoribbon, with the folded border parallel to the armchair direction.

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Figure 2: a) HREM image of a folded graphene membrane. b) Strain component along the direction perpendicular to the border, as reconstructed from a. c) Strain profile over region 1 in b. The compression of 4% close to the edge corresponds to a slope of 16% over a region of 3nm. d) 3D structure of the folded edge reconstructed from the strain profile.

Scanning Probe Microscopy on Graphene Quantum Dots

M. Morgenstern , D. Subramaniam , F. Libisch , Y. Li , C. Pauly , V. Geringer , R. Reiter , 1 1 2 4 4 3 1 T. Mashoff , M. Liebmann , J. Burgdörfer , C. Busse , T. Michely , R. Mazzarello , M. Pratzer 1

II. Institute of Physics and JARA-FIT, RWTH Aachen, D-52075 Aachen, Germany Institute for Theoretical Physics, Vienna University of Technology, A-1040 Vienna, Austria Institute for Theoretical Solid State Physics and JARA-FIT, RWTH Aachen University, D-52074 Aachen, Germany 4 II. Physikalisches Institut, Universität zu Köln, Zülpicherstrasse 77, D-50937 Köln, Germany 2 3

mmorgens@physik.rwth-aachen.de

I will present data of wave function mapping in graphene quantum dots deposited on an Ir(111) surface [1]. These quantum dots are confined exclusively by zig-zag edges. However, edge states are absent due to an exchange interaction of the π-bands of graphene with the dz2 surface states of the Ir(111) as evidenced by a combination of density functional theory calculations and scanning tunneling spectroscopy data. The same exchange interaction, which gets continuously smaller away from the edges, leads to a weak confinement of the quantum dot states. It turns out that this weak confinement is decisive to achieve rather regular wave functions within the quantum dots as observed experimentally (Fig. 1). Good agreement for the wave function energies is achieved by a simple analytic model, but careful analysis of the probed wave function patterns reveals that their appearance is additionally influenced by the penetration of an sp-like surface state of Ir(111) into graphene. In addition, I will show how graphene quantum dots can be produced on graphene flakes by local anodic oxidation using an atomic force microscope. References [1] D. Subramaniam et al., Phys. Rev. Lett. 108 (2012) 046801.

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Figure 1: Scanning tunneling spectroscopy images (upper line) of a graphene quantum dot deposited on Ir(111) in comparison with the local density of states calculated by a tight binding model (lower line). Measurement voltages and energies are indicated [1].

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“Is the Future Black? The Chemist’s Search for Graphene and Carbon Materials”

Klaus Müllen Max-Planck-Institute for Polymer Research, Mainz, 55128, Germany muellen@mpip-mainz.mpg.de

Research into energy technologies and electronic devices is strongly governed by the available materials. More recently, carbon allotropes and carbon-rich molecules play an increasingly important role as electronic conductors, semiconductors and catalysts and are attractive alternatives to established organic and inorganic materials. The unique physical and chemical properties of the two-dimensional (2D) πelectron system graphene ask for its chemical synthesis. We introduce a synthetic route to graphenes which is based upon the cyclodehydrogenation (“graphitization”) of well-defined dendritic (3D) polyphenylene precursors. This approach is superior to physical methods of graphene formation such as chemical vapour deposition or exfoliation in terms of its (i) size and shape control, (ii) structural perfection, and (iii) processability (solution, melt, and even gas phase). Columnar superstructures assembled from these nanographene discs serve as charge transport channels in electronic devices. Field-effect transistors (FETs), solar cells, and sensors are described as examples and their exemplary performance is discussed in terms of supramolecular order and interfacing. Upon pyrolysis in confining geometries or “carbomesophases”, the above carbon-rich 2D- and 3Dmacromolecules transform into unprecedented carbon materials and their carbon-metal nanocomposites. Exciting applications are shown for battery cells and fuel cells. In the latter case, nitrogen-containing graphenes serve as catalysts for oxygen reduction whose efficiency is superior to that of platinum. Further, transparent and conducting window-electrodes are fabricated which can replace ITO.

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References Feng, X., Marcon, V., Pisula, W., Hansen, M. R., Kirkpatrick, J., Andrienko, D., Kremer, K., Müllen, K., Nature Mater. 2009, 8, 421; Pang, S., Tsao, H. N., Feng, X., Müllen, K., Adv. Mater. 2009, 21, 3488; Yang, S., Feng, X., Zhi, L., Cao, Q., Maier, J., Müllen, K., Adv. Mater. 2010, 22, 838; Liu, R., Wu, D., Feng, X., Müllen, K., Angew. Chem. Int. Ed. 2010, 49, 2565; Käfer, D., Bashir, A., Dou, X., Witte, G., Müllen, K., Wöll, C., Adv. Mater. 2010, 22, 384; S. Blankenburg, M. Bieri, R. Fasel, K. Müllen, C.A. Pignedoli, D. Passerone, Small 2010, 6, 2266; Diez-Perez, I., Li, Z., Hihath, J., Li, J., Zhang, C., Zang, X., Zang, L., Dai, Y., Heng, X., Müllen, K., Tao, N., Nature Commun. 2010, 1, 31, DOI: 10.1038/1029; Liang, Y.; Schwab, M. G.; Zhi, L. J.; Mugnaioli, E.; Kolb, U.; Feng, X.L.; Müllen, K., J. Am. Chem. Soc. 2010, 132, 15030; Yang, S.; Feng, X.; Ivanovic, S.; Müllen, K., Angew. Chem. Int. Ed. 2010, 49, 8408; Yang, S., Feng, X., Wang, L., Tang, K., Maier, J., Müllen, K., Angew. Chem. Int. Ed. 2010, 49, 4795; Cai, J., Ruffieux, P., Jaafar, R., Bieri, M., Braun, T., Blankenburg, S., Muoth, M., Seitsonen, A. P., Saleh, M., Feng, X., Müllen, K., Fasel, R., Nature 2010, 466, 470; Treier, M., Pignedoli, C. A., Laino, T., Rieger, R., Müllen, K., Passerone, D., Fasel, R., Nature Chem. 2011, 3, 61; Liu, R., von Malotki, C., Arnold, L., Koshino, N., Higashimura, H., Müllen, K., J. Am. Chem. Soc. 2011, 133, 10372; Jimenez-Garcia L., Kaltbeitzel A., Enkelmann V., Gutmann J. S., Klapper M., Müllen K., Adv. Funct. Mater. 2011, 21 (12), 2216; Bieri M., Blankenburg S., Kivala M., Pignedoli C. A., Ruffieux P., Müllen K., Fasel R., Chem. Commun. 2011, 47, 10239; Li, H. L., Pang S. P., Wu S., Feng X. L., Müllen K., Bubeck C., J. Am. Chem. Soc. 2011, 133, 9423.

Graphene on the reconstructed Pt(100) surface and its interaction with atomic hydrogen

L. Nilsson, M. Andersen, R. Balog, J. Bjerre, E. Lægsgaard, B. Hammer, F. Besenbacher, I. Stensgaard and L. Hornekær Interdisciplinary Nanoscience Center and Department of Physics and Astronomy, University of Aarhus, Denmark Louis@inano.au.dk

Introduction Despite an enormous development for graphene fabrication within the last eight years, the production of high quality, large scale graphene by cost efficient routes needs further improvements to meet industry standards [1]. A fundamental understanding of the growth of graphene is therefore of utmost importance. Here, we demonstrate, from an interplay between STM and DFT calculations, that a graphene sheet can be grown continuously on the hex-reconstructed Pt(100) surface even across step edges and domain boundaries in the platinum substrate [2]. To address the challenge of opening a band gap in graphene, we have recently presented results demonstrating a band gap opening in graphene on Ir(111) by patterned hydrogen adsorption [3]. The resulting patterned adsorption structure was facilitated by the interaction between the iridium substrate and the graphene sheet. To obtain a better understanding of the role of the substrate, we investigate the interaction between hydrogen atoms and graphene grown on the reconstructed Pt(100) surface by STM and temperature programmed desorption (TPD) experiments combined with DFT calculations. Techniques STM measurements were performed using the so-called Aarhus STM. The Pt (100) surface was cleaned by numerous cycles of 2 keV Ne sputtering and annealing up to 1000°C, combined with annealing in O2 at 700°C, followed by flashes to 900°C. The cleanliness of the surface was checked with STM. Synthesis of graphene was typically carried out by exposing the Pt surface to 100-200 L of either ethylene or propylene (C3H6) at pressures in the low 10-7 torr range and a sample temperature of 700°C, with periodic flashes to 900°C. A commercial “Hydrogen Atomic Beam Source, HABS-40” was used to expose the surface to thermally cracked atomic hydrogen atoms.

Results and Discussion A continuous graphene sheet has been grown on the well-known Pt(100)-hex-R0.7 reconstruction[4]. Interestingly, the reconstruction of the platinum substrate is still present after the growth of graphene (figure 1). The graphene is found to grow across step edges and domain boundaries (figure 1) and thereby

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The calculations regarding edge dislocation lines in graphene involved supercells with hundreds of atoms and were therefore (for reasons of computational efficiency) performed with the Siesta code. Exchange and correlation effects were described using the GGA functional of Perdew, Burke and Ernzerhof (PBE).

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The DFT calculations regarding rotated sheets of graphene on a Pt(111) surface were performed with the semi-local meta-GGA density functional M06-L implemented in the real-space projector augmented wave GPAW code.

forming a continuous sheet. For domain boundaries of 7 degrees, the graphene is observed to rotate by incorporating defects similar to the Stone-Wales defects [5]. From STM it is revealed that the graphene sheet tends to have either an armchair or a zigzag direction aligned with the direction of the reconstruction of the platinum surface, however, other angles are also observed. The observed energy difference between different orientations of the graphene on the substrate is accordingly found to be small from DFT calculations. We also present a combined STM and TPD investigation of the interaction of the graphene with atomic hydrogen. At low coverage, the hydrogen atoms are observed from STM to form dimer structures similar to those observed previously on HOPG, and the desorption energy found from TPD is also similar to that found for HOPG [6]. At higher coverage the reconstruction of the platinum substrate is lifted and extended structures are depicted by STM. From TPD a distinct shift in desorption energies is observed. The experimental data indicate that the platinum substrate plays an active role in stabilizing these adsorbate structures on graphene. The experimental findings are supported by DFT calculations. References [1] Bae S, Kim H, Lee Y, Xu XF, Park JS, Zheng Y, et al. Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nature Nanotechnology. 2010;5(8):574-8. [2] Nilsson L, Andersen M, Bjerre J, Balog R, Hammer B, HornekĂŚr L, et al. Preservation of the Pt(100) surface reconstruction after growth of a continuous layer of graphene. Surface Science. 2012;606(3-4):464-9. [3] Balog R, Jorgensen B, Nilsson L, Andersen M, Rienks E, Bianchi M, et al. Bandgap opening in graphene induced by patterned hydrogen adsorption. Nature Materials. 2010;9(4):315-9. [4] Borg A, Hilmen AM, Bergene E. STM studies of clean, CO-exposed and O2-exposed Pt(100)-hex-R0.7-degrees. Surface Science. 1994;306(1-2):10-20. [5] Duplock EJ, Scheffler M, Lindan PJD. Hallmark of perfect graphene. Physical Review Letters. 2004;92(22):225502. [6] Hornekaer L, Sljivancanin Z, Xu W, Otero R, Rauls E, Stensgaard I, et al. Metastable structures and recombination pathways for atomic hydrogen on the graphite (0001) surface. Physical Review Letters. 2006;96(15):156104.

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Figure 1: STM image of a graphene area with a domain boundary between two perpendicular domains of the underlying hex-reconstructed Pt(100) surface. The white lines indicate zigzag directions in the graphene.

Graphene-based nanomaterials for field emission applications

Alexander N. Obraztsov, Victor V. Kleshch, Petr V. Shvets, Alexander P. Volkov Department of Physics, M.V. Lomonosov Moscow State University, Moscow 119991, Russia obraz@polly.phys.msu.ru

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We report here our recent results on investigation of field electron emission from graphene-based nanocarbon film materials. The films were obtained using chemical vapor deposition (CVD) from methane\hydrogen gas mixture activated by a direct current discharge. Si wafers, Ni or other metal sheets with dimensions up to 50 mm in diameter were used as the substrates. The field emission cathodes were made from the CVD films consisting of tiny graphite flakes with few graphene layers (of 2 to 50) oriented perpendicularly to substrate surface (see Fig. 1). Composition, structure and surface morphology of the nano-graphite films were analyzed with Raman, SEM and HR TEM (see, e.g. [1]). Our investigations of the field emission characteristics of the CVD films shown that this material combine advantages of CNT species (high aspect ratio, chemical inertness etc.) with other characteristics required for practical applications in vacuum electronic devices [2]. To demonstrate abilities of the nano-graphite cold cathodes we have developed device prototypes of the cathodoluminescent light sources (see, e.g. [2, 3] and Fig. 2). The record characteristics were demonstrated for these light sources including power efficiency (more than 10% for green light) and life time (exciding 10000 hours). Other developed device prototypes created with use of the nano-graphite cold cathodes include X-ray source, electro-mechanical oscillators [4], electron guns for particle accelerators and for application in an electric solar wind sail which is a space propulsion concept that uses the natural solar wind dynamic pressure for production spacecraft thrust [5].

ABSTRACTS

Field electron emission (FE) phenomenon has been a matter of considerable interest for purely academic and applied science since it was discovered in 1897. In contrast to other electron emission mechanisms (thermionic or photo emission) the field emission doesn’t need any power supply. Owing to this reason the field emission is frequently referred to as “cold” and corresponding electron emitters as “cold cathodes.” The FE is registered only at large electric field strength requiring an extremely high voltage to be applied between the flat cathode and anode. To reduce the voltage down to the values, which are practically suitable for vacuum electronic devices and for research purposes, the creation of emitters in form of needles with high aspect ratio is required. One of the most attractive features of the FE is its potential ability to provide the electron emission with very high current density. However, emitting surface area of a single emitter with high aspect ratio is usually quite small. Thus, to obtain electron beams with reasonable value of total current, the FE cathodes must contain arrays of numerous emitters. The abilities to produce such kind of micron-sized FE cathodes were demonstrated previously using Si and some other semiconductors and hard metals. However conventional lithographic technique of fabrication of such FE cathodes is complicated and expensive hampering wide application of the cold cathodes made of these materials. Since 1990s the interest to the FE has been triggered by the discovery of carbon nanotubes (CNT) and other types of nanocarbons. Having graphitic type atomic structure these nanostructured materials possess advantageous properties for efficient field emission: strong interatomic bonds and corresponding chemical inertness and robustness to ion bombardment; high conductivity and electron mobility, providing low resistive heating and voltage drop across emitter body; and high aspect ratios of the individual nanostructures, allowing usage of moderate voltages.

References [1] [2] [3] [4] [5]

A.N. Obraztsov et al., Carbon 46 (2008) 963. A.N. Obraztsov, V.I. Kleshch, J. Nanoelectronics and Optoelectronics 4 (2009) 207. A.N. Obraztsov, Cathodoluminescent light source (2002), Patent RU 2274924, EP1498931, US7683530. V.I. Kleshch, et al., ETP Letters 90 (2009) 464 P. Janhunen, et al., Rev. Sci. Instr. 81 (2010) 111301.

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Figure 1: SEM image of the nano-graphite CVD film morphology (a) and HR TEM image of the top end of a graphite flake composing the film.

Figure 2: The photographs of the cathodoluminescent lamps with the nano-graphite cold cathodes accordingly to [3].

Graphene for laser applications

E.D. Obraztsova , M.G. Rybin , A.V. Tausenev , V.A. Shotniev , V.R. Sorochenko , 1 1 P.S. Rusakov , I.I. Kondrashov 1 2

A.M. Prokhorov General Physics Institute, RAS, 38 Vavilov street, 119991, Moscow, Russia Avesta-Project Limited Liability Company, Troitsk, Moscow Region, Russia elobr@mail.ru

Since 2009 graphene is becoming more and more popular as a material for the ultrafast nonlinear optical modulators, working in a wide spectral range– so called “saturable absorbers” [1,2]. These elements introduced into the laser cavity allow transformation of a continuous wave (cw) output laser radiation into a train of sub-picosecond pulses. An important advantage of graphene is a possibility to realize a modelocking regime in a much wider spectral range (at least from 1um to 12 um), than the range covered by single-wall carbon nanotubes [3-6]. In this work we review our new data on synthesis [7,8], characterization [9] and application of graphene sheets for realization of the mode-locking regime with an output pulse duration of 200 fs in Er fiber laser (with a working wavelength of 1.55 um). The average output power was about 2.3 MW. The repetition rate was 34.2 MHz. A unique potential of graphene for formation of the saturable absorbers for a mid-IR range (~5-6 um (CO laser) and ~ 10 um (CO2 laser)) is also discussed. The work was supported by RAS research programs and RFBR projects-10-02-00792 and 11-02-92121.

References

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Bao L.J., Zhang H., Wang Yu et al., Adv. Func. Materials 2009, 19, 3077. Sun Z., Hasan T., Torrisi F., Popa D. et al., ACS Nano 2010,4,803. Il’ichev N.N., Obraztsova E.D., Garnov S.V. et al., Quantum Electronics 2004, 34, 572 [Garnov S.V., S.A. Solokhin, E.D. Obraztsova et al., Las. Phys. Lett. 2007, 4, 648. Solodyankin M.A., Obraztsova E.D., Lobach A.S. et al., Opt. Lett. 2008, 33,1336. A.V. Tausenev, E.D. Obraztsova, A.S. Lobach et al., Appl. Phys. Lett. 2008, 92, 171113 . Rybin M.G., Pozharov A.S. and Obraztsova E.D., Phys.Stat. Solidi C, 2010, 7, 2785. M. G. Rybin, P. K. Kolmychek, E. D. Obraztsova et al., J. Nanoelectron. Optoelectron. 4(2) (2009) 239. Obraztsov P.A., Rybin M.G., Turnina A.V. et al. , NanoLetters, 2011,11,1540.

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[1] [2] [3] [4] [5] [6] [7] [8] [9]

Introduction

Vincenzo Palermo CNR Bologna, Italy www.isof.cnr.it/nanochemistry/

A main advantage of graphene technology is that, being based on carbon, it takes advantage of the huge power and versatility of carbon-based organic chemistry, which allows a fantastic diversification of properties and functionalities at the nanoscale. Graphene can be chemically functionalized exactly like organic molecules; on the other hand, Graphene stands as a very suitable electronic platform material giving its close chemical affinity with organic molecules, from π-conjugated materials, to fullerene, carbon nanotubes or DNA. Graphene properties can therefore be widely enriched and diversified by using organic chemistry, through chemical doping, and molecular or atomic functionalization of its surface. Controlled chemistry of graphene and production of hybrid materials could thus overcome current technological locks, paving the way to considerable improvements of graphene-based devices performances and enlargement of the spectrum of applications, from high frequency devices, to switches and chemical sensors. The “GRAPHENE CHEMISTRY & MATERIALS” workshop aims at validating the roadmap developed within the GRAPHENE FLAGSHIP Pilot initiative, in particular in the fields of graphene chemical functionalization for electronics and composites applications, by an open consultation with leading experts in the field.

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Quantum Hall measurements on epitaxial graphene with oxygen adsorption

E. Pallecchi , M. Ridene , D. Kazazis , C. Mathieu , F. Schopfer , W. Poirier , D. Mailly , and A. 1 Ouerghi 1 2

CNRS - Laboratoire de Photonique et de Nanostructures, Route de Nozay, 91460 Marcoussis Laboratoire National de Metrologie et d'Essais, 29 Avenue Roger Hennequin, 78197 Trappes, France

emiliano.pallecchi@lpn.cnrs.fr

Graphene’s unique electronic properties make it an ideal play ground for mesoscopic physics and a promising candidate for novel electronics devices. The development of techniques capable of producing large area high quality graphene has further increased the interest for such a material. In epitaxial graphene (EG) grown on SiC the first carbon layer, also called the buffer layer, does not show graphitic signature and is responsible for large electron doping of graphene, typically on the order of 1013cm-2. Therefore, several techniques such as molecular doping, photochemical gating, and hydrogenation have been used to decreases the carrier concentrations. We report on low temperature transport measurement on oxygen-adsorped epitaxial graphene grown on SiC. From the low field Hall resistivity we extract a carrier concentration on the order of 8 x 1011 cm-2 which is more than one order of magnitude smaller than typical values of intrinsic epitaxial graphene. The reduction of electron doping is consistent with estimates from ARPES measurements performed prior to and after oxygen exposure. We find a fully developed quantum Hall effect over large distances of 50 µm, with a plateau at ν=2 and a vanishing longitudinal resistance. Such a plateau is the hallmark of single layer graphene and suggests that the buffer layer is not fully decoupled from the silicon carbide substrate. Finally, we show that annealing in vacuum of the sample results in an increase of the carrier concentration, up to values typical of intrinsic graphene on the order of 1013 cm-2.

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These observations are relevant for understanding oxygen adsorption on epitaxial graphene and for applications to fields such as metrology and quantum devices.

Characterization and manipulation of graphene using AFM

Bae Ho Park Konkuk University, Korea baehpark@konkuk.ac.kr

Monolayer graphene is one of the most interesting materials applicable to next-generation electronic devices due to its transport properties. However, realization of graphene devices requires suitable nanoscale lithography as well as a method to open a band gap in monolayer graphene. Nanoscale hydrogenation and oxidation are promising methods to open an energy band gap by modification of surface structures and to fabricate nanostructures such as graphene nanoribbons (GNRs). Until now it has been difficult to fabricate nanoscale devices consisting of both hydrogenated and oxidized graphene because the hydrogenation of graphene requires a complicated process composed of large-scale chemical modification, nanoscale patterning, and etching. I will report on nanoscale hydrogenation and oxidation of graphene under normal atmospheric conditions and at room temperature without etching, wet process, or even any gas treatment by controlling just an external bias through atomic force microscope lithography.[1] On the other hand, graphene produced by mechanical exfoliation has not been able to provide and ideal graphene with performance comparable to that predicted by theory, and structural and/or electronic defects have been proposed as one cause of reduced performance. I will report the observation of domains on exfoliated monolayer graphene that differ by their friction characteristics, as measured by friction force microscopy.[2] Angle-dependent scanning reveals friction anisotropy with a periodicity of 180â ° on each friction domain, as shown in Fig. 1. The frictioni anisotropy decreases as the applied load increases. It is proposed that the domains arise from ripple distortions that give rise to anisotropic friction in each domain as a result of the anisotropic puckering of the graphene.

References

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[1] Ik-Su Byun, Duhee Yoon, Jin Sik Choi, Inrok Hwang, Duk Hyun Lee, Mi Jung Lee, Tomoji Kawai, Young-Woo Son, Quanxi Jia, Hyeonsik Cheong, and Bae Ho Park, ACS Nano 5, 6417 (2011). [2] Jin Sik Choi, Jin-Soo Kim, Ik-Su Byun, Duk Hyun Lee, Mi Jung Lee, Bae Ho Park, Changgu Lee, Duhee Yoon, Hyeonsik Cheong, Ki Ho Lee, Young-Woo Son, Jeong Young Park, and Miquel Salmeron, Science 333, 607 (2011).

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Figure 1: (A) Friction force images showing the changing friction contrast as the sample is rotated counterclockwise from 0⁰ to 184⁰ relative to the horizontal scan direction (red dashed arrow). Roman numerals indicate the three friction domains. (B) Normalized friction force versus rotation angle for each domain, showing 180⁰ periodicity. The lines show that the variations in friction can be fitted by a simple sine modulus function.

Reversible Hydrogen Storage by Controlled Buckling of Graphene Layers

Vittorio Pellegrini CNR and Scuola Normale Superiore, Pisa, Italy *

Graphene is an intriguing material that shows promises for hydrogen storage. We shall present in this talk theoretical and experimental evidence that by changing the curvature of graphene, the energy barrier for adsorbing and desorbing atomic hydrogen attached to the pi-bonds of graphene can be removed making it possible to attach and release hydrogen at room temperature, a mechanism that can be exploited for room temperature hydrogen storage applications. By means of calculations based on density-functional theory, we demonstrate a tunability of the binding energies of more than 2 eV by changing the sheet out-of-plane deformation up to +-0.2Å, with the convex regions allocating the energetically favored hydrogen binding sites. We simulate the process of hydrogen chemisorption on corrugated graphene and release under the application of time-dependent mechanical deformations. Our results show that the corrugation of the graphene sheet and the controlled inversion of its curvature yield fast and efficient storage and release of hydrogen [1]. Our corrugated graphene device can potentially reach gravimetric capacities up to 8%wt and reversibly store and release hydrogen by external control of the local curvature at room conditions and with fast kinetics. Initial experimental tests of the capacity of corrugated graphene to bind hydrogen are carried out on epitaxial graphene grown on SiC(0001). The initial carbon layer (also known as the interface, zerolayer or buffer layer) below the monolayer graphene has been theoretically predicted to have a high curvature with an amplitude of 1.2Å over a length of ~2nm making it an optimal laboratory for testing the interaction between hydrogen and graphene as a function of curvature [2]. To this end we shall discuss scanning tunneling microscopy experiments of hydrogenated graphene sheets grown on the silicon face of silicon carbide. In these experiments we were able to atomically resolve, for the first time, the hexagonal lattice of the zerolayer verifying that it is topologically identical to monolayer graphene [3]. Upon obtaining atomic resolution, we hydrogenated the sample in situ and studied the position of hydrogen atoms on the graphene lattice as a function of curvature [4]. We found that atomic hydrogen binds to the carbon atoms in the convexly curved areas, in agreement with our theoretical evaluations based on DFT calculations [1], which indicates an increase of ~0.15eV in binding energy with respect to flat graphene (0.7eV). We finally measured the carbon hydrogen bond height to be ~1Å, in agreement with the expected bond length of 1.1Å [1].

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* Work done in collaboration with S. Goler,C. Coletti,V. Tozzini, T. Mashoff, M. Morandini, K. V. Emtsev, S. Forti, U. Starke, F. Beltram, and S. Heun References [1] [2] [3] [4]

V. Tozzini and V. Pellegrini. J. Phys. Chem. C115, 25523 (2011). F. Varchon et al. Phys. Rev. B 77, 235412 (2008). S. Goler et al. submitted; arXiv:1111.4918 S. Goler et al. in preparation.

Chemical Solutions to Exfoliate Graphite

Alain Pénicaud Université de Bordeaux - CNRS, Centre de Recherche Paul Pascal, 33600 Pessac, France penicaud@crpp-bordeaux.cnrs.fr

Graphite is insoluble in all media but may be dispersed with surfactants and/or sonication to obtain metastables suspensions. However, some graphite intercalation compounds (GICs) have been shown to be spontaneously soluble in polar organic solvents without the need for any kind of additional energy, such as sonication or high shear mixing.[1-3] Solutions of negatively charged graphene flakes have been prepared in low boiling point solvents such as tetrahydrofurane (THF) by dissolution of the graphite intercalation compound (GIC) KC8. In contrast with difficult-to-handle and/or carcinogenic solvents, such as NMP, dissolving graphene flakes in solvent such as THF opens up routes towards composites. Light scattering analysis allows to detect, in situ, the presence of two-dimensional objects in solution, with an average lateral size of over one micron. High resolution transmission electron microscopy analysis shows that the solubilized graphene flakes are exclusively single and double layers with no evidence for thicker species. References

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[1] C. Vallés and A. Pénicaud, patent (2007) WO 2009/087287; FR 07/05803 august 9, 2007. [2] C. Vallés et al., J. Am. Chem. Soc., 130, (2008) 15802-15804 [3] A. Catheline, C. Vallés, C. Drummond, L. Ortolani, V. Morandi, M. Marcaccio, M. Iurlo, F. Paolucci, A. Pénicaud, "Graphene solutions", Chem. Commun. 47, 2011, 5470-5472

Reactivity of Graphene Sheets: Cycloadditions and Rolling up to form Nanotubes

Maurizio Prato Center of Excellence for Nanostructured Materials (CENMAT), INSTM UdR di Trieste, Dipartimento di Scienze Chimiche e Farmaceutiche, University of Trieste, Trieste, Italy prato@units.it

The production of graphene by micromechanical cleavage has triggered an enormous experimental activity. Since then, many studies have demonstrated that graphene monolayers possess novel structural, electrical and mechanical properties. However many important issues need to be addressed before this material can be used. Much work has been produced on the chemical functionalization as a tool for tuning graphene chemical and physical properties. For example, chemical functionalization can make graphene dispersible in many solvents. To exploit the high mobility of graphene, the band gap engineering and controllable doping of semimetal graphene can be achieved by chemical functionalization. Moreover, the non-uniformity of graphene edges and the potential for dangling bonds are thought to have significant influence on their chemical properties and reactivity. Chemical modification of various forms of graphene, including reduced graphene oxide, liquid-phase exfoliated graphite, pristine graphene and its multilayers has been obtained. For instance, the aryl diazonium-based reaction has been extensively studied as a specific radical reaction on graphene layers. In graphene, the edges exhibit a higher reactivity than the interior during this specific reaction. Instead, we have recently reported the functionalization of graphene layers by condensation of a protected Îą-amino acid and paraformaldehyde, demonstrating that even if the reactivity of graphene differs from that of fullerenes and carbon nanotubes, the 1,3-dipolar cycloaddition can be efficiently performed and yields a highly functionalized material taking place not just at the edges but also at the C=C bonds in the center of graphene sheets. However, further work needs to be performed for understanding the chemical structure of the functionalized graphene and their reaction mechanisms.

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In this work we present a detailed study on the reactivity of graphene sheets stabilized in DMF using two different reactions: the 1,3-dipolar cycloaddition reaction and the amide-bond condensation reaction achieved between the free carboxylic groups already present in the exfoliated graphene and the amino functionalities of the attached moieties. In addition, we will show that under certain circumstances, graphene layers can be rolled up to form carbon nanotubes.

MSM photodetector based on gold decorated graphene ink

Antonio Radoi1, Alina Cismaru1, George Konstantinidis1, Mircea Dragoman2 1

National Institute for Research and Development in Microtechnology (IMT-Bucharest), Str. Erou Iancu Nicolae 126 A, 077190, Voluntari-Bucharest, Romania 2 Foundation for Research & Technology Hellas (FORTH) P.O. BOX 1527, Vassilika Vouton, Heraklion 711 10, Crete, Greece antonio.radoi@imt.ro

Graphene is a single atom monolayer of carbon atoms, has many applications in optics and optoelectronics [1] competing important applications in nanoelectronics [2]. Several methods are used to fabricate graphene: mechanical exfoliation, epitaxial growth and advanced chemical vapor deposition (CVD) techniques [3]. Graphene monolayer flakes, obtained via mechanical exfoliation and deposited over interdigitated (IDT) electrodes, were recently used for the photodetection at 1.55 Îźm with a responsivity of 6.1 mA/W [4]. Lately, graphene inks are a promising alternative for graphene device implementation especially in optoelectronic domain (see Ref. 5 and the references herein). In this communication, we have used a combination of top-down and bottom-up approaches to fabricate a graphene photodetector. Our device consists of a MSM IDT bimetallic electrodes (Au/Pt) array (see Figure 1a) deposited on high resistivity (HR) Si wafer over which gold decorated graphene dispersion has been casted. The Au-Pt IDT array was manufactured on HR Si substrate using standard metallization techniques and photolithography. Pristine graphene nanoplatelets (PureSheets QUATTRO, NanoIntegris, USA) were purified by removing the surfactant and re-suspension in distilled water. A certain aliquots of graphene dispersion was allowed to dry onto glass slides and further used in the metallization process. After gold has been deposited using sputtering procedure, scanning electron microscopy investigations (SEM) revealed nanosized gold platelets (Figure 1b).

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From the above figure we can see that in the UV-VIS spectral region when 100% of the power lamp is illuminating the photodetector, the current is increasing more than 10 times (from ~90 nA up to ~1.2 mA at V=8 V). In the case of IR, the current is increasing about 40 times when compared to dark current. Further tests are currently under investigation.

ABSTRACTS

The I-V measurements were made with the semiconductor characterization system Keithley 4200, connected to a dark Faraday cage and the light was incident directly on the device. Due to the relatively high mobility of the photogenerated electrons and holes and the small gaps between IDT fingers (1 mm), a significant photoresponse is achieved before carrier recombination. The I-V characteristics were first recorded at dark and for illumination with a halogen lamp, which generates a tunable power with a maximum of 150 W in the visible spectrum. Also, an IR source consisting of a tungsten halogen lamp with a power of 0.5 mW, which extend the spectral domain from 1500 nm to 2500 nm was used. The resulted I-V responses are depicted in Figure 2.

Authors acknowledge that this work was supported by a grant of Romanian National Authority for Scientific Research, CNCS-UEFISCDI, project number PN-II-ID-PCE-2011-3-0071

References

[1] [2] [3] [4] [5]

F. Bonaccorso, Z. Sun, T. Hasan, A. C. Ferrari, Nature Photonics, 4, (2010), 611. M. Dragoman, D. Dragoman, Progress in Quantum Electronics, 33, (2009),165. C. Soldano, A. Mahmood, E. Dujardin, Carbon 48, (2010), 2127. T. Mueller, F. Xia, P. Avouris, Nature Photonics, 4, (2010), 297. A. Radoi, A. Iordanescu, A. Cismaru, D. Dragoman and M. Dragoman, Nanotechnology, 21 (2010) 455202.

Figures

Figure 1: Interdigitated (IDT) bimetallic (Au/Pt) electrodes (a); SEM micrograph of gold decorated graphene nanoplatelets

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Figure.2: The I-V response of graphene ink photodetector under various illuminatons.

CVD Growth and Applications of Graphene with Millimetre-Size Single-Crystal Grains and Three-Dimensional Interconnected Graphene Networks Wencai Ren, Libo Gao, Zongping Chen, and Hui-Ming Cheng Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China wcren@imr.ac.cn

Graphene has attracted increasing interests because of its unique two-dimensional structure, many fascinating properties such as giant electron mobility, extremely high thermal conductivity, and extraordinary elasticity and stiffness, as well as a wide range of technological applications [1,2]. Large single-crystal graphene is highly desired and essentially important for the applications of graphene in electronics since grain boundaries between graphene grains markedly degrade its quality and property. However, graphene prepared so far is usually stitched together from nanometer to micrometer grains. In addition, integration of individual two-dimensional graphene into macroscopic structures is also very important for the application of graphene. A series of graphene-based composites and macroscopic structures have been recently fabricated using chemically-derived graphene sheets. However, these composites and structures suffer from poor electrical conductivity because of the low quality and/or high inter-sheet junction contact resistance of the chemically-derived graphene sheets.

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Besides two-dimensional growth of graphene, we have also realized the direct synthesis of a threedimensional (3D) porous graphene macrostructure by template-directed CVD, which we call graphene foam (GF) [4]. This porous graphene bulk material consists of an interconnected network of graphene, which is flexible and has fast transport channel of charge carriers for high electrical conductivity. Even with a GF loading as low as 0.5 weight percent, GF/poly (dimethyl siloxane) (PDMS) composites show a very high electrical conductivity of 10 S/cm, 6 orders of magnitude higher than chemically-derived graphenebased composites. Using this unique network structure and the outstanding electrical and mechanical properties of GFs, as an example, we demonstrate the possibility of GF/PDMS composites for flexible, foldable and stretchable conductors [4]. Recently, we found that this unique 3D macrostructure also show a great potential for high-sensitivity gas detection [5].

ABSTRACTS

Here, we show the growth of millimeter-size hexagonal single-crystal graphene grains and graphene films joint from such grains on Pt substrates by ambient-pressure chemical vapour deposition (CVD) [3], which are more than 50 times larger than the biggest hexagonal single-crystal grains reported until now. Moreover, we proposed a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to the graphene but also to the Pt substrates [3]. The Pt substrates can be repeatedly used for graphene growth with almost no limit, and the graphene obtained on a repeatedly-used Pt substrate has almost the same quality as that obtained originally. In contrast, the commonly-used transfer process is mainly based on substrate etching, which not only leads to inevitable damage to graphene, metal residues on graphene, and serious environmental pollution but also greatly increases the production cost. In addition, such etching methods are not suitable for the transfer of graphene from chemically inert substrates. These single-crystal graphene obtained shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility greater than 7,000 cm2V-1s-1 under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its non-destructive transfer will enable various applications.

References

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[1] A. K. Geim, K.S. Novoselov, Nature Materials 3 (2007) 183. [2] A. K. Geim, Science 5934 (2009) 1530. [3] L. B. Gao, W.C. Ren, H.L. Xu, L. Jin, Z.X. Wang, T. Ma, L.P. Ma, Z.Y. Zhang, Q. Fu, L.M. Peng, X.H. Bao, H.M Cheng, Nature Communications DOI: 10.1038/ncomms1702. [4] Z. P. Chen, W.C. Ren, L.B. Gao, B.L. Liu, S.F. Pei, H.M. Cheng, Nature Materials 10 (2011) 424. [5] F. Yavari, Z.P. Chen, A.V. Thomas, W.C. Ren, H.M. Cheng, N. Koratkar, Scientific Reports DOI: 10.1038/srep00166.

A local optical probe for measuring motion and stress in a nanoelectromechanical system

Antoine Reserbat-Plantey, Laëtitia Marty, Olivier Arcizet, Nedjma Bendiab, Vincent Bouchiat Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble Cedex 9, France antoine.reserbat-plantey@grenoble.cnrs.fr

Nanoelectromechanical systems can be operated as ultrasensitive mass sensors and ultrahigh frequency resonators, and can also be used to explore fundamental physical phenomena such as nonlinear damping and quantum effects in macroscopic objects. Various dissipation mechanisms are known to limit the mechanical quality factors of nanoelectromechanical systems and to induce aging due to material degradation, so there is a need for methods that can probe the motion of these systems, and the stresses within them, at the nanoscale. Here, we report a non-invasive local optical probe for the quantitative measurement of motion and stress within a nanoelectromechanical system based on Fizeau interferometry and Raman spectroscopy. The system consists of a multilayer graphene resonator that is clamped to a gold film on an oxidized silicon surface. The resonator and the surface both act as mirrors and therefore define an optical cavity. Fizeau interferometry provides a calibrated measurement of the motion of the resonator, while Raman spectroscopy can probe the strain within the system and allows a purely spectral detection of mechanical resonance at the nanoscale. References [1] Bunch, S.J. et al, Science, 315 (2007) 490. [2] Otakar, F. et al, Nature Communications, 2 (2011) 255. [3] Reserbat-Plantey, A. Marty, L. Arcizet, O. Bendiab, N. and Bouchiat, V. Nature Nanotechnology, accepted 15/12/11

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Figure 1: a: Whitelight optical image of a wedged MLG cantilever showing iridescence. Scale bar represents 5 μm. b: Schematic view of the device : electrical excitation and optical detection, either with a photodiode (intensity) or a Raman spectrometer (intensity and spectral data). c: Variations in G peak intensity (▲) and position (⊙) under MLG electrostatic actuation, revealing peak softening at maximum cantilever deviation. The lower dashed line represents the drive voltage. d: Lock-in amplitude (dark line) as a function of the drive frequency showing a resonant peak at ω0 = 1.3 MHz. The position of the Raman G peak (•) shows a softening, which coincides with the mechanical resonance of the MLG cantilever.

ABSTRACTS

Figures

Supramolecular chemistry and (nano)graphenes: a honeymoon?

Paolo SamorĂŹ ISIS - University of Strasbourg & CNRS 7006, 8 allĂŠe Gaspard Monge, 67000 Strasbourg, France samori@isis-ulp.org

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Multifunctional materials based on Ď&#x20AC;-conjugated systems, and in particular on (nano)graphenes, are key in organic (opto)electronics. However, their practical use requires the optimization of the self-assembly of multimodular architectures at surfaces using non-conventional methods, their controlled manipulation and responsiveness to external stimuli, and the quantitative study of various physico-chemical properties at distinct length- and time-scales. My lecture will review our recent findings on the bottom-up fabrication of graphene based conducting architectures and materials as well as the use of multicomponent systems, in particular based on responsive and semiconducting molecules, in order to realise multifunctional devices such as optically switchable field-effect transistors.

Spin manipulation of organometallics by strain engineering of defected graphene

Biplab Sanyal , Sumanta Bhandary , Saurabh Ghosh , Heike Herper , Heiko Wende , Olle 1 Eriksson 1

Dept. of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala, Sweden School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA 3 Faculty of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Lotharstrasse 1, 47048 Duisburg, Germany 2

Biplab.Sanyal@physics.uu.se

In organic nanospintronics, one of the objectives is to manipulate the spin states of organic molecules [1] with a d-electron center, by suitable external means, e.g., temperature pressure, light etc. In organometallics, the central atom with unpaired d-electrons can have several spin states available, e.g., low, intermediate and high spin states. If the external agent is able to overcome the energy barrier, one may move from one spin-state to other. For example, in iron porphyrin (FeP) molecule in the gas phase, the ground state has a S=1 spin state with another higher energy minimum at S=2 spin state, which is reachable by crossing an energy barrier of around 0.8 eV. Very recently, we have demonstrated [2] by first principles density functional calculations that a strain induced change of the spin state, from S=1 to S=2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in the sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation.

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We also predict that the spin state change may be detected in x-ray magnetic circular dichroism (XMCD) experiments. Our calculated values for the spin-dipole contribution <Tz> is quite large (7<Tz> = -1.89 ÎźB and 1.32 ÎźB) for 0% strained (S=1) and 1% strained (S=2) graphene lattice, respectively. Therefore, the measured effective moments (sum of spin moment and spin-dipole moment) will be quite different for the two spin states. The other detection method is the magnetic anisotropy in XMCD experiment. The magnetic anisotropy energy (MAE) and hence, the easy axis of magnetization can be calculated by adding the spin-orbit coupling term in the Hamiltonian. We have used second-order perturbation theory and a 4level model with HOMO, HOMO-1, LUMO and LUMO+1 states, (HOMO and LUMO being highest occupied molecular orbital and lowest unoccupied molecular orbital respectively) to calculate MAE. We predict that for the S=1 state, Fe will have an out of plane easy axis of magnetization with a MAE of 0.4 meV whereas, S=2 spin state yields an in-plane magnetization with a MAE of 2 meV. Considering these two prominent effects, it is expected that the change in the spin state should be easily detectable in experiments.

ABSTRACTS

The effect is demonstrated in Fig. 1, where the molecular energy diagrams are shown for two spin states along with the magnetization densities for the highest occupied molecular orbital (HOMO). Two situations are shown (0% and 1% strain of the graphene lattice). When graphene is strained, the divacancy site on which FeP is situated affects the bond length between Fe and N in FeP. As a result, the occupancies in the molecular level changes and gives rise to a spin state change from S=1 to S=2. The magnetization densities clearly show the nature of dz2 and dx2-y2 orbitals of Fe in FeP for S=1 and S=2 spin states respectively.

References [1] H. Wende et al., Nat. Mater. 6, 516 (2007). [2] S. Bhandary, S. Ghosh, H. Herper, H. Wende, O. Eriksson and B. Sanyal, Phys. Rev. Lett. 107, 257202 (2011).

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Figure 1: Magnetization density isosurfaces for FeP on (left) 0% and (right) 1% strained graphene. The isosurfaces have been plotted for an energy window of 0.4 eV below the Fermi levels in both cases. The spin densities shown in the left up (side view) and right down (top view) parts correspond to spin-up and spin-down channels, respectively. The energy levels with the d-orbital character of FeP are shown in the extreme left and right for 0% and 1% strained graphene, respectively.

Potential of thermally conductive polymers based on carbon allotropes in the development of new heat management components on board a car 1

Alberto Fina , Guido Saracco , Samuele Porro , Fabrizio Pirri , Franco Anzioso and 3 Carloandrea Malvicino 1 2 3

Politecnico di Torino, Department of Applied Science and Technology, Torino, Italy Italian Institute of Technology, Centre for Space Human Robotics, Torino, Italy Centro Ricerche FIAT, Orbassano, Italy

Thermally conductive polymer nano-composites based on carbon allotropes (graphite, graphene and nanotubes) offer new possibilities for replacing metal parts in several applications, including power electronics, electric motors and generators, heat exchangers etc. The polymer brings in advantages such as light weight, corrosion resistance and ease of processing; the nanofiller, to be distributed according to a perculating network enabling phonon transfer, ensures sufficient thermal conductivity (a few W/mk). In the automotive sector, the tremendous challenge of reduction of CO2 emissions, forces car manufacturers to improve drastically the heat recovery chain as more than 60% of the fuel energy gets actually lost. A survey of all the potential applications of carbon-based conductive polymers will be offered relying on the expertise of a large car manufacturer. Several heat exchangers systems offer indeed good application opportunities, including intercoolers, air conditioning condensers and evaporators as well as novel radiators hosted in the car chassis to substitute those based on frontal air intake which affect significantly the vehicle aerodynamics. Unusually high thermal conductivity, in the range of a few thousands of W/mK 1, makes graphene and carbon nanotubes the best promising candidate material for thermally conductive composites. However, our experimental results, arising from the EU project Thermonano 2 and reviewed in this presentation, show that it is not trivial to reach the desired heat conductivities 3. The bottleneck is the large interfacial thermal resistance between the nanoparticles, which hinders the transfer of phonon dominating heat conduction in carbon materials. In order to overcome this limitation, the aspect ratio and platelet-like nature of graphene are beneficial, owing to the higher overlap obtainable with graphene compared to CNT. The best compromise between cost and performance was found by a combination of different allotropes, the carbon nanotubes bridging graphene or graphite platelets 4.

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In the presentation the complete development line of a prototype plate heat exchanger obtained by injection moulding for an intercooler application will be disclosed and benchmarked against current heat exchangers enlightening considerable economic margins.

ABSTRACTS

The compounding method and the plastic moulding process was found to have a significant importance in ensuring the desired nanostructure. In this context, the graphene low apparent density poses specific challenges and plays against a facile inclusion in the polymer matrix. Functionalisation of graphene platelets may help in this context. Furthermore, to maximise the efficiency of particle/particle thermal contact, the exploitation of self-structuring of nanoparticles in polymer blends is envisaged, based on the excellent results recently obtained by this research group on micronic graphite-based polymer composites 4.

Finally, some ideas will be discussed to functionalize the nanofilled polymer heat exchangers with sensing capabilities or increased surface conductivity. Graphene-based materials can indeed be solubilized and transferred into nanoparticle-based inks or deposited through layer-by-layer deposition 5.

References

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[1] J. Su, M. Cao, L. Ren, C. Hu, J. Phys. Chem. C, 115 (2011) 14469 [2] www.thermonano.org [3] Z. Han, A. Fina. Thermal Conductivity of Carbon Nanotubes and their Polymer Nanocomposites: A Review. Prog. Polym. Sci. 36 (2011) 914â&#x20AC;&#x201C;944 [4] A. Fina, , Z. Han, G. Saracco, U. Gross, M. Mainil. Morphology and Conduction Properties of Graphite Filled Immiscible PVDF/PPgMA Blends. Polymers for Advanced Technologies 2012, in press [5] Laufer G., Carosio F., Martinez R., Camino G., Grunlan Jc. (2011) Growth and fire resistance of colloidal silicapolyelectrolite thin film assemblies. In: JOURNAL OF COLLOID AND INTERFACE SCIENCE, vol. 356 n. 1, pp. 69-77

Size-Selective Carbon Nanoclusters as Precursors to the Growth of Epitaxial Graphene

R. Schaub, B. Wang, X.-F. Ma, M. Caffio and W.-X. Li Scottish Centre for Interdisciplinary Surface Spectroscopy, School of Chemistry University of St Andrews, St Andrews, KY16 9ST renald,schaub@st-andrews.ac.uk

The nucleation and growth mechanisms of epitaxial graphene on a Rh(111) surface will be presented [1]. STM and DFT calculations show that carbon nano-islands form in the initial stages of graphene growth using ethylene as the carbon source, possessing an exclusive size of 7 honeycomb carbon units (hereafter labeled as 7C6). These magic-sized clusters adopt a dome-like hexagonal shape indicating that bonding to the substrate is localized on the peripheral C atoms. Smoluchowski ripening is identified as the dominant mechanism leading to the formation of graphene, with the size-selective carbon islands as precursors. Control experiments and calculations, whereby coronene molecules, the hydrogenated analogues of 7C6, are deposited on Rh(111), provide an unambiguous structural and chemical identification of the 7C6 building blocks. References [1] B. Wang, X.-F. Ma, M. Caffio, R. Schaub, W.-X. Li, Nano Letters, 11 (2011) 424.

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Figure 1: Ball-and-stick model (left) and high resolution STM image (right) of the size-selective 7C6 nanoclusters identified as precursors to the growth of graphene on a Rh(111) surface.

Large Area Plasma-Enhanced Chemical Vapor Deposition of Nanocrystalline Graphite on Insulator for Electronic Device Application 1

Marek E. Schmidt , Cigang Xu , Mike Cooke , Hiroshi Mizuta , Harold M.H. Chong 1

Nano Research Group, School of Electronics and Computer Science, University of Southampton, Highfield, Southampton, UK Oxford Instruments Plasma Technology, North End, Yatton, Bristol, UK

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mets09r@ecs.soton.ac.uk

This paper reports on large area plasma-enhanced chemical vapor deposition (PECVD) of nanocrystalline graphite (NCG) on thermally grown SiO2 wafer, quartz and sapphire substrates. Grown films are evaluated using Raman spectroscopy, ellipsometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrical characterization and optical transmission measurements indicate promising properties of this material for use as transparent electrodes and for electronic device application. A plasma-based etch process for NCG has been developed. Recently, growth of NCG on sapphire by molecular beam epitaxy has been reported [1]. This process, however, requires ultra high vacuum compared to PECVD. Our contribution is a step towards large area direct growth of few layer graphene on insulating substrates by PECVD, thus eliminating the required transfer of graphene grown on metal catalysts by CVD [2]. The NC-graphite film is deposited using an Oxford Instruments Nanofab 1000 Agile tool, which allows processing of wafers up to 8” in size. The table temperature is measured by a thermocouple below the susceptor on which the substrate sits; the actual temperature of the samples is lower. In this work a thermally oxidized 150 mm diameter silicon wafer was used for deposition. Quartz and sapphire samples of 11x11 mm2 in size were used in a separate run for comparison. The process chamber is first conditioned with hydrogen at 1000 mT and a flow rate of 100 sccm. This is followed by a heat-up procedure from loading temperature of 700°C to the processing temperature of 900°C. The deposition is based on introduction of methane and hydrogen at 60 sccm and 75 sccm, respectively, at a pressure of 1500 mT and RF power of 100 W. As-deposited NCG films are analyzed using a Rennishaw InVia Raman spectrometer with 532 nm laser excitation wavelength. Typical Raman spectra of as-deposited NCG on SiO2, quartz and sapphire are shown in Fig 1. All spectra exhibit distinct D, G and 2D peaks at around 1350, 1600 and 2700 cm-1, respectively. The G peak position is unaffected by the excitation wavelength (532, 633 and 785 nm), and the intensity ratio of the D to G peak is ~2.3. These observations are in accordance with previous reports on Raman spectra of NCG [3]. The in-plane correlation length La = 21 Å is estimated from the D/G peak intensity ratio [4]. Figure 2 shows an SEM micrograph of the surface topology of a 35 nm thick NCG film on SiO2. The roughness RMS of 1.17 nm for this film was obtained from a 1x1 μm2 large AFM scan. This is an increase compared to 0.1 ± 0.02 nm for the underlying SiO2. The thickness uniformity of the NCG film grown on a 150 nm wafer (shown in Fig. 3) was measured by ellipsometry, with results shown in Fig. 4. The central 7x7cm2 area of the wafer (see dotted line in Fig. 4) was mapped using Raman spectroscopy (532 nm, 5 mm data point spacing). The obtained distribution of the D to G peak intensity ratio is shown in Fig. 5. Four-point hall measurement on 35 nm thick NCG on SiO2 was used to obtain the sheet resistance RS=3728Ω/sq, mobility μ = 2.49 cm2/Vs and carrier concentration N = 1.8x1020 cm-3. Additionally, simple electrical structures were fabricated on various samples for resistance measurements and film thickness measurements by AFM. First, we pattern 4 and 50 μm wide lines with various lengths using photolithography. This is followed by reactive ion etching of the NCG film in 20 sccm O2, 20 mT pressure

and 20 W RF power with an etch rate of 5 nm/min. After resist strip using N-Methyl-2- pyrrolidone (NMP), Ti/Au contacts are realized by photolithography and subsequent lift-off in NMP, as shown in Fig. 6. For these processed films, bulk resistivity of ρ = 0.029 Ωcm was obtained from two-probe measurement. The optical transmission of an as-deposited 6.6 nm thick NCG on quartz glass was measured and is above 80% across the visible spectrum. Current work involves optimization of NCG film thickness uniformity and process tuning for thinner films with larger crystalline domains. Acknowledgements: This work was supported by the University of Southampton, School of Electronics and Computer Science Scholarship and the Southampton Nanofabrication Centre. References [1] [2] [3] [4]

S. Jerng, D. Yu, Y. Kim, J. Ryou, S. Hong, C. Kim, S. Yoon, et al. J. Phys. Chem. C, 2011, 115 (11), pp 4491–4494 A.K. Geim, Science, 324(5934) (2009), 1530-1534. A. C. Ferrari and J. Robertson, Phil. Trans. R. Soc. A 362 (2004), pp 2477–2512. A. C. Ferrari and J. Robertson, Physical Review B, 61(20) (2000), 14095.

Figure 2: SEM close-up of as-deposited NCG film on thermal oxide.

Figure 3: Photograph of 150 mm wafer with NCG film. British penny shown for size comparison.

Figure 4: Ellipsometer thickness mapping of NCG film grown on 150 mm wafer.

Figure 5: Distribution of Raman D to G peak intensity of central part of 150 mm wafer. Mapping area indicated in Fig 4.

Figure 6: SEM micrograph of NCG film patterned into two 4 μm wide ribbons and contacted by Ti/Au.

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Figure 1: Raman spectra of NCG on thermally grown SiO2, sapphire and quartz glass.

ABSTRACTS

Figures

Gapped ground state in suspended bilayer graphene

F. Freitag, J. Trbovic, A. Baumgartner, R. Maurand, M. Weiss, and C. Schönenberger Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland

Bilayer graphene is an exciting material, widely extending the range of phenomena as compared to monolayer graphene. In bilayer graphene a gap can be opened by applying a potential difference between the two layers, for example. Furthermore, the eight-fold ground-state degeneracy of the zero-energy Landau level provides a large Hilbert space with novel composite particles, and due to the added mass, Coulomb interaction is expected to be much larger than in monolayer graphene when the carrier density is reduced. It has already been shown that the eight-fold ground state degeneracy can be lifted in a magnetic field. Here we show that high-mobility suspended bilayer graphene devices allow for a spontaneous gap formation at zero magnetic field [1] (similar work is reported in [2]) The properties of this gap are investigated by means of electronic transport measurements in magnetic field as a function of gatevoltage, source-drain bias voltage, and temperature. We find a very pronounced dip in the conductance at the charge neutrality point in a rather narrow gate-voltage window. The differential finite-bias conductance (dI/dV) reveals two kinds of gaps: a wide one of size 2meV with a shape that mimics the BCS density-of-states and a smaller one of size 0.5meV. When repeating current annealing we find samples where the conductance is vanishing fully over the whole width of the large gap and samples for which the conductance does not vanish at the charge-neutrality point. For the latter the conductance rather appears to saturate at low temperatures at a value that is independent of the applied magnetic field. The minimum conductance of 0.2 e2/h at 230mK is however much lower than the typical minimum conductance values in monolayer graphene. We will also discuss recent four terminal measurements on suspended bilayer graphene. We discuss the origin of the gaps in terms of the various many-electron broken symmetry states that have been put forward by theory in recent years. References [1] F. Freitag, J. Trbovic, M. Weiss, and C. Schönenberger, arXiv:1104.3816, Phys. Rev. Lett. In press [2] J. Velasco Jr., L. Jing, W. Bao, Y. Lee, P. Kratz, V. Aji, M. Bockrath, C.N. Lau, C. Varma, R. Stillwell, D. Smirnov, Fan Zhang, J. Jung, A.H. MacDonald arXiv:1108.1609

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Figures

Figure 1: Differential conductance Gd=dI/dV measured as a function of source-drain bias voltage Vsd and back-gate voltage Vg. A pronounced gap forms around the charge neutrality point.

Anisotropic quantum Hall effect in graphene on stepped SiC surfaces

T. Schumann, K.-J. Friedland, M. H. Oliveira, Jr., A. Tahraoui, J. M. J. Lopes, H. Riechert Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany schumann@pdi-berlin.de

With its two-dimensional nature and extraordinary electrical properties, graphene is one of the most promising materials for future electronic applications. The synthesis of graphene by the depletion of Si from the surface of SiC is thereby of particular technological interest, since it offers the possibility of preparing graphene on a large scale directly on an insulating substrate. Epitaxial graphene prepared on the hexagonal SiC(0001) face exhibits a stepped surface with regular terraces and step edges with graphene growing carpet-like over the complete substrate and forming a closed layer. The influence of steps on the electrical transport at zero magnetic field has recently been studied by different groups [1,2]. It was shown that step edges and monolayer-bilayer junctions contribute to an intrinsic resistance. Other works [3] show that the electrical properties (i.e. carrier concentration and mobility) are not altered by the existence of step edges. Besides these works, little research has been done to determine the influence of the steps on the SiC surface on the transport properties of graphene, especially in the presence of magnetic fields. Here, we report on an anisotropic behavior of the magnetotransport in graphene at high magnetic fields for Hall bars aligned parallel and perpendicular to surface terraces. Monolayer graphene was prepared on semi-insulating 6H-SiC(0001) substrates with a miscut of ~1%. Subsequently, Hall bars with a width of 2 μm and a length of 30 μm, oriented perpendicular or parallel to the step edges on the surface, were defined by optical lithography and oxygen plasma etching. Their surface morphology was investigated by atomic force microscopy and their structural quality by Raman line scans. The Raman scans (not shown) reveal a strong variation in the position of the G- and 2D-line for Hall bars oriented perpendicular to the terraces (i.e. crossing several step edges).

To interpret this anisotropy, we adopt a simple model (figure 2). At high magnetic fields, the conductivity is governed by a low number of channels at both edges of the Hall bar. The number of conductive channels

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However, the longitudinal resistivities show a quite different behavior for the two alignments at high magnetic fields. While the Hall bar oriented parallel to the terraces shows a conventional quantum Hall effect, the resistivity shows an overall increase with increasing magnetic field in the case where the current crosses many surface steps. This behavior can not only be an effect of enhanced scattering, e. g. at defects or impurities, since the resistivity at zero magnetic field is comparable. The anisotropy at high fields strongly indicates an influence of the steps of the SiC substrate on the magnetotransport properties of epitaxial graphene.

ABSTRACTS

Hall- (ρxy) and longitudinal (ρxx) resistivity were measured at a temperature of 320 mK and magnetic fields (B) perpendicular to the surface up to 14 T. The results are shown in figure 1. In both cases, the Hall resistances at high magnetic fields show for both directions a similar behavior with only one clearly recognizable Hall plateau. Carrier densities n and mobilities μ were derived from the Hall coefficients and the resistivities at zero magnetic field.

is given by the filling factor ﾎｽ and is proportional to n/B. In the region of the step edges, additional conductive channels (corresponding to higher filling factors) may appear. One reason may be the lower effective magnetic field (Beff ~0.9 B0) at the steps, caused by the tilt between the SiC surface (and hence the graphene) and the step facet. A second reason might be differences in carrier concentration between step edges and terraces. These additional channels enable the possibility that electrons scatter between channels at opposite sides, since the spatial separation between the additional edge channels is reduced. This enhances the backscattering, as indicated in Fig. 3, and may increase the longitudinal resistance at high magnetic fields.

References [1] M. K. Yakes et al. Nano Letters 10, 5 (2010) 1559. [2] S.-H. Ji et al. Nature Materials 10, 11 (2011) 114. [3] J. Jobst et al. Solid State Communications 151, 16 (2011) 1061.

Figures

Figure 1: Longitudinal- (ﾏ』x) and Hall resistivity (ﾏ』y) as a function of magnetic field (B) in Hall bar structures, aligned parallel (black) and perpendicular (red) to the SiC terraces, respectively.

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Figure 2: Model of the magnetotransport in graphene for narrow Hall bars on stepped SiC surfaces in side-view (a) and top view (b).

Graphene Technology Platform at BASF

Matthias Schwab BASF SE Technology Incubator - Graphene Research GVM/I - J550, 67056 Ludwigshafen, Germany matthias.schwab@basf.com

Graphene as an emerging material has recently spurred the interest of scientific research both in academia and industry. At BASF graphene and graphene materials are currently being studied for several potential fields of application. We have set up a graphene technology platform aiming at the systematic investigation of this new carbon material fabricated either by top-down or bottom-up procedures. Owing to its appealing electrical conductivity, graphene can be used for conductive formulations and coatings as well as for polymer composite materials with antistatic properties. Also, graphene may serve as a new carbon material thus replacing or complementing traditional carbon black additives in lithium-ion batteries as well as activated carbons in supercapacitor devices. It is also intended to evaluate graphene-based transparent conductive layers for their use in displays, organic solar cells and organic light emitting diodes. On a longer perspective the semi-conducting properties of graphene nanoribbons fabricated from chemical bottom-up approaches shall be explored.

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The talk will focus on the recent activities of BASF in the field of graphene and provide an evaluation of this promising material from an industrial point of view.

Transfer-Free Grown Bilayer Graphene Transistors with Ultra-High On/Off-Current Ratio

Pia Juliane Wessely1, Frank Wessely1, Emrah Birinci1, Bernadette Riedinger2, Udo Schwalke1 1

Institute for Semiconductor Technology and Nanoelectronics (ISTN), Technische Universität Darmstadt, Schlossgartenstraße 8, 64289 Darmstadt, Germany 2 Fraunhofer-Institut für Werkstoffmechanik, Wöhlerstraße 11, 79108 Freiburg, Germany

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1. Introduction: In this paper we report on monolayer graphene transistors (MoLGFETs) and bilayer graphene field effect transistors (BiLGFETs) which grow transfer-free on oxidized silicon wafers. By means of catalytic chemical vapor deposition (CCVD) in-situ grown MoLGFETs and BiLGFETs, respectively, are realized directly on oxidized silicon substrate, whereby the number of stacked graphene layers is determined by the selected CCVD process parameters, e.g. temperature and gas mixture. First experimental evidence demonstrating the feasibility of this transfer-free graphene growth method has already been published in November 2009 [1, 2]. The results of a Fourier-analysis of transmission electron microscopy (TEM) data of a fewlayer graphene sample revealed the crystalline properties of the graphene multilayer more in detail as published in April 2011 [3]. In fact, the observed interplanar spacing of 3.5Å is a strong evidence for the existence of fewlayer graphene grown by means of CCVD. Furthermore, the combination of atomic force microscopy examination, Raman spectroscopy as well as extensive electrical characterization of graphene structures on silicon dioxide confirms the suitability of this novel in-situ CCVD growth process [4, 5, 6]. MoLGFETs exhibit the typically low on/off-current ratio of 16 and show the typical Dirac point. In contrast, BiLGFETs exhibit ultra-high on/off-current ratios of 107, exceeding previously reported values by several orders of magnitude. The transfer characteristic shows a pure unipolar p-type device behavior. Besides the excellent device characteristics, the complete CCVD fabrication-process is silicon CMOS compatible. This will allow a simple and low-cost integration of graphene devices for nanoelectronic applications in a hybrid silicon CMOS environment. 2. Results and Discussion: The electrical characterization of the graphene devices is performed using a Keithley SCS 4200 semiconductor parameter analyzer. The catalyst areas are simultaneously used as source and drain contacts [5]. An illustration of the device is shown in Fig. 1a. Fig. 1b shows the transfer characteristic of a MoLGFET. The current flow from source to drain (IDS) is measured as a function of the applied backgate voltage (VBG), swept from -15V to 15V and reverse, while a constant voltage between drain and source (VDS) of 3V is applied. The Dirac-point at VBG = -6V confirms the existence of electron and hole conduction as expected for graphene [7]. The electrical characterization of several MoLGFETs shows an average hysteresis value of VBG,MoLGFET = 16.8V ± 20% [6]. However, for in-situ CCVD grown graphene FETs the maximum current is limited by the thin nickel conducting paths as well as the high contact resistance caused by some carbon deposits on top of the source drain regions [5]. Fig. 1c shows the current voltage characteristics of a typical in-situ CCVD grown BiLGFET depending on the applied backgate voltage (VBG), exhibiting an on/off-current ratio of 1x107 at room temperature. Furthermore, when increasing the ambient temperature to 200°C, the on/off-current ratio only degrades slightly by one order of magnitude for BiLGFETs [8]. The needed bandgap is partly induced by the applied backgate voltage. Accordingly, we suspect that additional effects, like intensive interactions between bilayer graphene and silicon dioxide are responsible to further enhance the bandgap. Such intensive interactions may develop during the growth of the bilayer graphene on the silicon dioxide at moderate temperatures under well defined ambient conditions within a CVD chamber [5]. Since substantial amounts of atomic hydrogen are

generated from the decomposition of methane during CCVD processing, it is likely that hydrogen atoms adsorb on the graphene surface or may be incorporated within the graphene bilayer. As a result, effects on the electronic properties such as increasing the bandgap are expected. All BiLGFETs show a clear unipolar p-type device behavior which is consistent with the output characteristic [5]. The selection of the carrier type (i.e. holes in this case) may be facilitated by additional doping and/or Schottky-barrier effects [8]. In-situ CCVD grown BiLGFETs exhibit an average hysteresis of VBG,BiLGFET = 19.5V ± 20% [6]. The observed hysteresis corresponds well to results on graphene devices obtained from other research groups [9]. The hysteresis in both kind of transistors, i.e. MoLGFETs and BiLGFETs, is attributed to trapping and detrapping of charges at the oxide-graphene interface [9]. 3. Conclusions: BiLGFETs exhibit ultra-high on/off-current ratios of 1x107 exceeding previously reported values by several orders of magnitude. We explain the improved device characteristics by a combination of effects, in particular graphene-substrate interactions, hydrogen doping and Schottky-barrier effects at the source/drain contacts as well. With this transfer-fee fabrication method hundreds of large scale BiLGFETs are realized simultaneously on one 2’’ wafer in a silicon CMOS compatible process. Acknowledgement: This research is part of the ELOGRAPH project within the ESF EuroGRAPHENE EUROCORES program and partially funded by the German Research Foundation (DFG, SCHW1173/7-1).

References

[1] [2] [3] [4] [5] [6] [7] [8] [9]

L. Rispal, U. Schwalke, SCS Trans., (2009) L. Rispal, P.J. Ginsel, U. Schwalke, ECS Trans., 33 (9) (2010), 13-19. P.J. Ginsel, F. Wessely, E. Birinci, U. Schwalke, IEEE DTIS (2011) P.J. Wessely, F. Wessely, E. Birinci, U. Schwalke, ECS Trans., (2011) in print P.J. Wessely, F. Wessely, E. Birinci, K. Beckmann, B. Riedinger, U. Schwalke, PhysicaE (2012), in print, http://arxiv.org/abs/1111.6397 P.J. Wessely, F. Wessely, E. Birinci, B. Riedinger, U. Schwalke, Electrochemical and Solid-State Letters, 15 (4) K1-K4 (2012) in print F. Schwierz, Nature Nanotechnology, 5, (2010) P.J. Wessely, F. Wessely, E. Birinci, B. Riedinger, U. Schwalke, ECS Trans., (2012) in print H. Wang, Y. Wu, C. Cong, J. Shang, T. Yu, ACS Nano 4, 12 (2010)

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Figure 1: (a) Schematic drawing of a graphene field effect device structure produced by CCVD using an aluminum/nickel catalyst system. (b) Current voltage characteristic of a monolayer graphene transistor as a function of the applied backgate voltage VBG exhibiting an on/off-current ratio of 16 at room temperature. (c) Current voltage characteristic of a bilayer graphene transistor as a function of the applied backgate voltage VBG exhibiting an on/off-current ratio of 1x107 at room temperature.

ABSTRACTS

Figures

Correlation of odd electrons in graphene: Effect on chemistry, magnetism, and mechanics

Elena Sheka Peoples’ Friendship University of Russia, Miklukho-Maklay str., 6, Moscow 117198, Russia sheka@icp.ac.ru

In the imagination of the majority of quantum computationists, involved in the graphene nanoscience, the motion of weakly bound odd electrons of graphene with different spins is not correlated. Only this fact can justify them using computational techniques based on single restricted closed-shell determinants such as widely used DFT schemes. Sometimes, the schemes have even been heralded as indisputable standard of the computations in the field. However, the electron behavior in graphene is much richer and does not fit a Procrustean bed of the electron correlation neglect just revealing peculiariries related to graphene edges, structurally inhomogeneous chemical reactivity, size-dependent magnetism, enhancement of the electron density of graphene bubles, and so forth. When speaking about electron correlation, one must address the problem to the configuration interaction (CI). However, neither full CI nor any its truncated version, clear and transparent conceptually, can be applied for computations, valuable in graphene nanoscience, so that techniques based on single unrestricted open shell determinants become the only alternative. UDFT and unrestricted Hartree-Fock (UHF) approaches form the techniques ground and are both sensitive to the electron correlation, but differently due to different dependence on electron spins. Nevertheless, one can suggest three characteristic parameters that may characterize the extent of the electron correlation and that can be evaluated within the framework of both techniques. Among the parameters there are the following: 1.

Misalignment of energy ΔERU=ER-EU

(1)

Here ER and EU present total energies calculated by using restricted and unrestricted versions of the same program; 2.

The number of effectively unpaired electrons

ND = trD ( r r ′ ) and ND = ∑ A DA ,

(2)

where D ( r r ′ ) and DA present the total and atom-fractioned spin density caused by the spin asymmetry due to location of electrons with different spins in different spaces; 3.

Misalignment of squared spin

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ΔSˆ 2 = SˆU2 - S(S + 1)

(3)

Here Sˆ U2 presents the squared spin value calculated within the applied unrestricted technique. Table 1 presents a set of the three parameters evaluated for a number of right-angled fragments (na,nz) of graphene (na and nz count the numbers of benzenoid units along armchair and zigzag edges of the fragment, respectively) by using AM1 version of semiempirical UHF approach. The first two parameters are definitely not zero by absolute value, besides greatly dependent of the fragment size. At the same time, their relative values are constant within ~10% accuracy pointing to a stable and size independent effect

caused by the electron correlation. Additionally, the relation ND = 2Sˆ U2 , which is characteristic for correlated electrons in the singlet state, is rigidly kept over all fragments.

Fragment ( na ,nz )

Odd electrons Nodd

(5, 5) (7, 7) (9, 9) (11, 10) (11, 12) (15, 12)

88 150 228 296 346 456

ΔE RU Kcal/mol

δE RU = ΔE RU / E R %

δND = ND / Nodd

307.6 376.2 641.6 760.1 900.6 1038.1

17 15 19 19 20 19

31 52.6 76.2 94.5 107.4 139

35 35 35 32 31 31

Sˆ 2

% 15.5 26.3 38.1 47.2 53.4 69.5

The data convincingly evidence that the electron correlation in graphene is significant. In view of the correlation, peculiarities of the graphene chemistry, magnetism, and mechanics can be explained at the quantitative level. Chemical reactivity of graphene is atomically mapped due to difference in values DA in (2). The value, whose expression should be properly adapted to the computational scheme in use, serves a quantitative indicator of the target atom at any step of the chemical addition and lays the foundation of computational synthesis of the graphene polyderivatives of any kind [1]. The electron correlation is the main reason for the species magnetism. In the case of graphene the magnetism is molecular by origin and size dependent since the values of the magnetic constant , small enough for the magnetic behavior of the singlet-ground-state species to become recordable, is achieved at the average linear size of the graphene fragment of a few nm. The magnetism obviously disappears when the size exceeds the electron mean free path [2]. Stretching graphene sheets results in strengthening the electron correlation thus providing increase in their unpairing, which leads to lifting the electron density in general, and atomic chemical reactivity, in particular [3], so that not a virtual magnetic field is responsible for a peculiar behavior of graphene bubles, but a predictable change in the electron density of a stretched object lays the feature foundation. General aspects of the odd electrons correlation related to sp2 nanocarbons and its manifestation in the electronic properties of the species are presented in [4].

E.F.Sheka and N.A.Popova, arXiv:1102.0922 [cond-mat.mes-hall], J Mol Mod (2012). E.F.Sheka, N.A.Popova, V.A.Popova, L.Kh. Shaymardanova, J Mol Mod 17 (2011) 1121. E.F.Sheka and L.A.Chernozatonskii, J Exp Theor Phys 110 (2010) 121. E.F.Sheka, Fullerenes: Nanochemistry, Nanomagnetism, Nanomedicine, Nanophotonics, CRC Press, Taylor&Francis Group, Boca Raton, 2011.

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[1] [2] [3] [4]

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References

Free standing graphene monolayer at high hydrostatic pressure

1,2

Alexander V. Soldatov , Shujie You , Mattias Mases , Konstantin S. Novoselov

Department of Applied Physics Mechanical Engineering, Lulea University of Technology, SE â&#x20AC;&#x201C; 971 87 Lulea, Sweden 2 Department of Physics, Harvard University, Cambridge, MA 02138, USA 3 School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK Alexander.Soldatov@ltu.se

We report on the first Raman study of free standing (FS) graphene monolayer (membrane) at high hydrostatic pressure in a diamond anvil cell (DAC). We were able to follow G - and G' band up to a pressure of 10 GPa. Both modes exhibit significant attenuation and linear hardening on pressure increase at a rate of 5.6-5.9 cm-1/GPa and 12 cm-1/GPa for G- and G' band respectively. The evolution of the bands frequency, width, and relative intensity with pressure is discussed in detail. The modes' Gruneisen parameter was determined and compared to that reported for uni- and bi-axial strain [1] and theoretical predictions. The graphene membrane behaviour at high hydrostatic pressure differs drastically from that of the single layer material deposited on a substrate [2] which obscures the intrinsic materialâ&#x20AC;&#x2122;s properties.

References

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[1] T. Mohiuddin, A. Lombardo, R. Nair, et al., Phys. Rev. B 79, (2009), 205433. [2] J.E Proctor, E. Gregoryanz, K.S. Novoselov, et al., Phys. Rev. B 80, (2009), 073408.

Graphene audio voltage amplifier

Roman Sordan, Erica Guerriero, Laura Giorgia Rizzi, Massimiliano Bianchi, Laura Polloni Department of Physics, Politecnico di Milano, Polo di Como, Via Anzani 42, 22100 Como, Italy roman.sordan@como.polimi.it

The main building block of analog electronics is a voltage amplifier: an electronic device capable of amplifying small alternating current (AC) voltage signals. Many graphene analog electronic devices, performing different functions,[1-5] have recently been proposed stemming from high carrier mobility[6,7] and ambipolar transport in graphene field effect transistors (FETs). However, none of these devices was capable of signal amplification, thus ultimately requiring integration with Si transistors for performing this most important task. Here we demonstrate an integrated graphene voltage amplifier paving the way for all graphene analog electronics.[8]

Even higher gains could be obtained with higher supply voltages, with the use of gate dielectrics with higher breakdown voltages. The obtained values demonstrate that, among other applications, the present graphene amplifier is suitable for high fidelity amplification of audio signals. The high voltage gain obtained in our devices can also be utilized to fabricate graphene digital logic gates which can be directly coupled.

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Figure 2a shows measured AC components of the input and output voltage signals of the amplifier biased at VDD = 2.5 V. At this supply voltage a maximum voltage gain |Av|max = 3.7 (11.4 dB) was measured at an input frequency f of 10 kHz. The frequency response of the fabricated amplifier in the frequency range f < 5 MHz is shown in Figure 2b. High gain is preserved at very low frequencies due to a direct coupling both at the input and output of the amplifier (i.e., there is no lower cut-off frequency). The gain remains constant up to about 20 kHz, and then decreases as the frequency is increased, dropping by 3 dB at the higher cut-off frequency f−3 dB = 70 kHz which also defines the bandwidth of the amplifier. The amplifier is capable of signal amplification up to a unity-gain frequency f1 = 360 kHz. At this frequency, the amplifier operates as a unity-gain amplifier (buffer), while for f > f1 it attenuates the input signal. The signal phase shift φ introduced by the amplifier is 180° at low frequencies (signal inversion), decreasing to 90° at high frequencies. Both amplitude and phase characteristics of the voltage gain indicate a typical dominant-pole (at f−3 dB) behavior. However, this pole does not originate from the amplifier but from the capacitances of the cables used to connect the amplifier to the measurement equipment (an intrinsic unity-gain frequency can be estimated to be ∼ 9 GHz).

ABSTRACTS

Signal amplification was obtained by fabricating graphene transistors in which the top Al/Al2O3 gate stack overlaps with the Ti/Au source and drain contacts (Figure 1a,b). A similar full-channel coverage exists in conventional Si metal-oxide-semiconductor FETs and allows maximum drain current modulation as there are no ungated parts of the channel that contribute to fixed series resistances which reduce the voltage gain. The Al2O3 layer which forms on the surface of the Al gate prevents short circuits between the contacts. The gate also serves as an additional heat sink which allows high drain currents ID and consequently high voltage gain Av. Additionally, as the gate fully covers the channel, desorption of adsorbates from graphene is suppressed at high drain currents, and therefore the electrical properties of FETs are stable during operation. Voltage amplifiers were realized in a complementary push-pull configuration (Figure 1c).

References

[1] [2] [3] [4] [5] [6]

H. Wang, D. Nezich, J. Kong, T. Palacios, IEEE Electron Device Lett. 30 (2009) 547 N. Harada, K. Yagi, S. Sato, N. Yokoyama, Appl. Phys. Lett. 96 (2010) 012102 X. Yang, G. Liu, A. A. Balandin, K. Mohanram, ACS Nano 4 (2010) 5532 A. Sagar, K. Balasubramanian, M. Burghard, K. Kern, R. Sordan, Appl. Phys. Lett. 99 (2011) 043307 X. Yang, G. Liu, M. Rostami, A. A. Balandin, K. Mohanram, IEEE Electron Device Lett. 32 (2011) 1328 K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, H. L. Stormer, Solid State Commun. 146 (2008) 351 [7] X. Du, I. Skachko, A. Barker, E. Y. Andrei, Nature Nanotech. 3 (2008) 491 [8] E. Guerriero, L. Polloni, L. G. Rizzi, M. Bianchi, G. Mondello, R. Sordan, Small 8 (2012) 357

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Figures

Figure 1: Integrated graphene voltage amplifier. a) A schematic of an amplifier. Source (VDD, GND) and drain (OUT) contacts (Ti/Au) overlap with gate (IN) contacts (Al; dark core) covered by an insulating layer (Al2O3; bright shell). b) A tilted scanning electron microscope image of a device. The arrows indicate the extent of the graphene flake. c) A circuit diagram of the amplifier. Z = 1 MΩ||13 pF is the input impedance of the oscilloscope used to measure input and output signals while 50 Ω is the output resistance of the input voltage source. Since |Z| >> 50 Ω the input signal fully drops across Z, i.e., vIN(t) = VIN+vin(t), where VIN is the DC bias voltage and vin(t) is the AC component of the input signal. The amplifier is additionally loaded with RL which simulates the input resistance of the next amplifying stage. This resistance was either infinite, 30 kΩ, or 10 kΩ, depending on the measurement.

Figure.2: Voltage amplification. a) AC components of the input and output voltage signals at a frequency f = 10 kHz for VDD = 2.5 V and RL → ∞. The voltage gain is Av = −3.7. The DC components of the signals are VIN = 0.15 V and VOUT = 1.15 V. b) Frequency response Av =|Av|∠ϕ of the amplifier for VDD = 2.5 V and RL→ ∞. Top: Magnitude |Av(f)| of the voltage gain. The magnitude decreases at 18 dB/dec at high frequencies, which is very close to the decrease of 20 dB/dec expected from a dominant pole at f−3 dB. Bottom: Phase shift ϕ (f) between output and input signals introduced by the amplifier.

Atomic Imaging and Spectroscopy of Single Layered Materials with Interrupted Periodicities

Kazu Suenaga Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, 305-8565, Japan suenaga-kazu@aist.go.jp

The interrupted periodicities (atomic defects or edge structures) are quite important especially in lowdimensional crystals since they strongly affect their physical and/or chemical properties. In bulk crystals electron microscopes have been widely used to examine structural defects such as dislocations and grain boundaries, which are regarded as one- and two-dimensional structural defects, respectively. In contrast, the individual point defects (zero-dimensional defects, such as mono-vacancies, impurity/dopant atoms) were believed to be difficult to investigate. Both atomic sensitivity and atomic resolution are required in the analytical techniques. After a monovacancy was first observed by TEM and proved to be stable even in low-dimensional carbon structures [1], studies of point defects in mono-layered materials have become very popular among scientists. Vacancies and topological defects in graphene are commonly examined at atomic level [2,3,4]. Defects and edge structures in hexagonal boron nitride (h-BN) are also a hot topic among physicists [5,6,7,8]. Recently, mono-vacancies have been successfully identified in WS2 nano-ribbons [9]. Here we show how HR-TEM and spatially resolved EELS can be applied to the studies of various singlelayered materials with the interrupted periodicities. Atomic defects and edge structures can be unambiguously identified with the elemental assignment. The inevitable delocalization of EELS signals is suggested to practically limit the achievement of using EELS for chemical mapping with atomic resolution. The boron monovacancy (VB) is assigned as a typical point defect by ADF imaging and EELS, and energyloss near edge fine structure (ELNES) is used to investigate the electronic states of nitrogen atoms around the point defect. The work provides an example of spectroscopic imaging based on the scanning transmission electron microscopy (STEM)-EELS techniques to demonstrate the possibilities of exploring the electronic states with single atom sensitivity. A JEM-2100F equipped with a delta corrector and cold field emission gun was operated at 60kV for these spectroscopy experiments [10,11]. A fast Frourier transform (FFT) of the typical ADF image shows that the microscope can resolve 0.108 nm in the STEM mode (not shown). The probe current was ~ 40 pA.

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This work was supported by Japan Science and Technology Agency under the CREST project.

ABSTRACTS

Fig. 1 shows an example of atomic defects in CVD graphene. The model structure involves pentagons and heptagons located at the boundary to accommodate the small angle boundary. A monovacancy in h-BN is examined by STEM-EELS (Fig. 2). The core-level spectroscopy on the nitrogen atoms at the vicinity of boron vacancy is successfully made [12].

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

A. Hashimoto et al., Nature, 430 (2004) pp.870-873 K. Suenaga et al., Nature Nanotech., 2 (2007) pp.358-360 J. Meyer et al., Nano lett., 8 (2008) pp.3582 C. O. Girit, et al., Science 323, 1705â&#x20AC;&#x201C;1708 (2009). C. Jin et al., Phys. Rev. Lett., 102, 195505 (2009) J. Meyer et al., Nano Lett., 9, 2683 (2009) N. Alem et al., Phys. Rev. B 80, 155425 (2009) O. Krivanek et al., Nature 464, 571-574 (2010) Z. Liu et al., Nat. Commun. 2, 213 (2011). T. Sasaki et al., J. Electron Microsc. 59, s7â&#x20AC;&#x201C;s13 (2010). K. Suenaga and M. Koshino, Nature 468, 1088-1090 (2010). K. Suenaga, H. Kobayashi, and M. Koshino, Phys. Rev. Lett., 108 075501 (2012).

Figures

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Figure 1: An example of 5-8-5 defect in graphene. (a) HR-TEM BF image, taken at 120kV. Octagon is almost at centar between two pentagons at up and down side (b) simulated TEM image and (c) relaxed atomic model. Octagon with yellow color and pentagon with blue color. Bar = 1nm. JEM 2010F with the CEOS corrector operated at 120kV.

Figure 2: Monovacancy in h-BN layer [13]. (a) ADF image shows a monovacacny in a single layer h-BN. Line-spectrum was recorded along the yellow line. (b) Schematic presentation (red: nitrogen, blue: boron) of boron monovacancy. (c) Nitrogen K-edge fine structures extracted from the line-spectrum. Each of three approximately corresponds to the probe positions marked in (b). A prominent prepeak in the nitrogen K-edge can be found at 392 eV in the spectrum recorded at the position 2, i.e., near the boron vacancy site.

Near 400 GHz World Fastest Graphene RF TransistorFor High Frequency Nanoelectronics and Circuits CMOS Platform Integration

Chun-Yung (C.Y) Sung IBM, United States

Graphene possesses great potential for radio frequency (RF) applications such as amplifiers and frequency mixers, whose performance can greatly benefit from the high carrier velocity of graphene. Ultra-high carrier mobility has been demonstrated in mechanically exfoliated flakes under ideal conditions (e.g. suspended graphene at low temperatures) which minimize external perturbations. In reality, technologically-relevant graphene devices require large-area synthesized graphene supported on and in contact with a substrate, i.e. under conditions where the graphene channels are inevitably affected by extrinsic perturbations. With large-area graphene becoming available by either CVD or epitaxial methods, it is of great importance to build devices from such technologically relevant graphene materials and to evaluate their performance on high-quality substrates like diamond-like carbon (DLC) and silicon carbide (SiC). Here we demonstrate RF field-effect transistors (FET) fabricated on wafer-scale CVD and epitaxial graphene, both achieving record cut-off frequencies surpassing >350 GHz at a scaled channel length of 40 nm. We also conduct a systematic study on the voltage gain and power gain of these graphene transistors, and demonstrate drastic performance enhancements through improvements in graphene quality, choice of dielectric materials and optimal doping of the graphene channel. Finally, we demonstrate the first graphene-based, amplifying integrated circuit, with a gain over 3 dB.

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While graphene transistors have proven capable of delivering GHz-range cut-off frequencies, applying the devices to RF circuits has been largely hindered by the lack of current saturation in the zero band gap graphene. Herein, the first high-frequency voltage amplifier is demonstrated using large-area chemical vapor deposition (CVD) grown graphene. The graphene field-effect transistor (GFET) has a 6-finger gate design with gate length of 500 nm. The graphene common-source amplifier exhibits ~5dB low frequency gain with the 3dB bandwidth greater than 6 GHz. This AC voltage gain demonstration of a GFET is attributed to the clear current saturation in the device, which is enabled by an ultrathin gate dielectric (4 nm HfO2) of the embedded gate structures. The device also shows extrinsic transconductance of 1.2 mS/Âľm at 1 V drain bias, the highest for graphene FETs using large-scale CVD graphene reported to date. The simulations are in good agreement with the measurements, validating the experimental demonstration of this graphene-based amplifier. The simulation also shows the device is capable of voltage amplification for frequencies exceeding 15 GHz. Compared with previously reported graphene analog circuits that always show the attenuation of the signal, this is the first time an AC gain has been reported. The nearly-constant frequency doubler performance over such a wide temperature range indicates that the graphene transconductance in both p and n branches is temperature independent in this range. To our knowledge, this is the first demonstration of this property in CVD graphene.

Figures

Figure 1: Small-signal current gain |h21| versus frequency for two 40 nm devices with peak fT of 300 GHz and 350 GHz, also consistent with the value derived from Gummelâ&#x20AC;&#x2122;s method shown in the inset.

(a)

(b)

Figure 2: The measured voltage gain versus drain current at 5 MHz with a maximum gain of 3 dB from an integrated circuit of graphene amplifier on wafer-scale epitaxial graphene on SiC.

(c)

Figure 3: (a) Schematic of graphene IC and the integration flow. The fabricated devices were protected by two layers of passivation. Finally, to form an RF IC, an inductor was integrated with a FET device. (b) Output characteristics of the same device. Strong current saturation and desired low gds are achieved. (c) gm, gds, and intrinsic voltage gain (Gin=gm/gds) as a function of Vds at Vgs=1.2 V.

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(a)

(b)

(c)

Figure 4: (a) Photograph of graphene IC using CVD graphene and embedded gates. Inductors were monolithically integrated with graphene FETs and the circuit was measured as a frequency doubler. A six-finger device was used in the circuit. (b) Captured image from the spectrum analyzer during the circuit operation. With input power of 0 dBm at 1GHz, the conversion gain is ~ -25 dB. (c) Measured frequency doubler performance over temperature for fIN=1GHz. This is an important advantage of this technology for high-temperature applications.

Linear band dispersion in multilayer epitaxial graphene grown on the SiC(000-1) C face

A. Taleb-Ibrahimi UR1 CNRS/Synchrotron SOLEIL, St Aubin Gif/Yvette Cedex France

Epitaxial graphene (EG) onto SiC is extremely promising for applications because it makes feasible carbon electronics while circumventing carbon nanotubes problems, i.e. scalability and contact problems. It is possible to grow exceptional quality graphene on both Si and C faces of SiC. For multilayer epitaxial graphene (MEG) grown on the C-face, a unique rotational stacking of the graphene layers causes adjacent graphene layers to be electronically decoupled. A set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K-point are observed, where each cone corresponds to an individual macroscale graphene sheet. The top layers in MEG are quasi neutral, with the Dirac point within experimental resolution from the Fermi level (about 10meV). This is in contrast to deviations to the linear dispersion observed elsewhere for highly doped EG on the Si-face indicating electron-phonon and electron-plasmon coupling (the Dirac point is 440 meV below EF). We will provide here direct experimental evidence of these observations using angle-resolved photoemission.

References

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[1] Sprinkle, M., Siegel, D., Hu, Y., Hicks, J., Soukiassian, P., Tejeda,A., Taleb-Ibrahimi, A., Le Fevre, P., Bertran,F., Vizzini, S., Enriquez, H., Chiang, S., Berger, C., De Heer, W., Lanzara, A., Conrad, E.H. Phys Rev Lett, 103, 226803. (2009). [2] Sprinkle, M., Hicks, J., Tejeda, A., Taleb-Ibrahimi, A., Le Fevre, P., Bertran, F., Tinkey, H., Clark, M. C., Soukiassian, P., Martinotti, D., Hass, J., & Conrad, E. H. Journal of Physics D: Applied Physics, 2010, 43(37): 374006. [3] Hicks, J., Sprinkle, M., Shepperd, K., Wang, F., Tejeda, A., Taleb-Ibrahimi, A., Bertran, F., Le Fevre, P., de Heer, W. A., Berger, C., Conrad, E. H. Physical Review B, 2011, 83(20): 205403

Observing early stages of growth and scaling graphene over 300mm wafers

Kenneth Teo , Andy Newham , Matthew Cole , Nalin Rupesinghe , Kemal Celebi , Jong Won 2 2 Choi and Hyung Gyu Park 1 2

AIXTRON, Cambridge, United Kingdom ETH Zurich, Zurich, Switzerland k.teo@aixtron.com

Here, we present our observations made during the early stages of graphene growth employing a chemical vapour deposition method with copper catalyst. Spectroscopic monitoring of surface catalysis showed that graphene crystals evolve from densely distributed nucleation points that interconnect to form large crystals covering the entire surface. Under certain conditions, secondary nucleation which form a second layer was observed inside the primary graphene crystals. Kinetics of growth and effective activation energy for the graphene synthesis will be discussed for a possible rate limiting step of the surface catalytic synthesis of graphene. Conditions for large-scale synthesis of monolayer graphene will be addressed in this talk. Growth and characterisation of graphene grown using copper films on silicon dioxide on silicon substrates were performed. Key considerations for scaling are discussed and graphene growth on the 300mm wafer scale was demonstrated.

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Figure 1: Evolution of graphene domains during growth

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Figure 2: Growth of graphene onto Cu/SiO2/Si wafers. Clockwise from top left: Raman spectroscopy, 300mm wafer, AIXTRON BM 300 automated equipment

Photocurrent in graphene n-n' junctions

Maxim Trushin, John Schliemann University of Regensburg, 93040 Regensburg, Germany Maxim.Trushin@physik.uni-regensburg.de

The carbon atoms in graphene are arranged in a honeycomb lattice, and due to its two interpenetrating Bravais sublattices the charge carriers acquire an additional degree of freedom known as pseudospin. The pseudospin orientation turns out to be coupled with the direction of particle motion in a way similar to the spin-orbit coupling in semiconductors, see Fig. 1. The pseudospin-dependent selection rule constrains the possible optical transitions between the valence and conduction bands in the presence of the linearly polarized light, see Fig. 1. The pseudospin selection rule in optical excitations can be understood from the effective interaction Hamiltonian which contains a coupling term between the pseudospin operators (Pauli matrices) and the vector potential characterizing a linearly polarized electromagnetic wave. The carriers have opposite pseudospin orientations in the valence and conduction bands. The pseudospin flip is necessary to excite any valence electron to the conduction band as long as momentum transfer is negligible. To be specific we set linear polarization along x-axis, i. e. the polarization angle is zero, as shown in Fig. 1. The interaction Hamiltonian is trying to rotate the pseudospin about the polarization direction. If the pseudospin and polarization direction are parallel with each other then the pseudospin orientation obviously does not change and the interband transition does not occur. In the opposite case, when the polarization is normal to the pseudospin orientation, the pseudospin can flip easily and the interband transition probability is maximal. As consequence the photovoltage measured on the irradiated n-n' junction depends strongly on the angle between the top contact long edge and light polarization plane. In contrast to the previous work [1] we employ the Boltzmann equation [2] which includes a built-in potential U(x) characterizing graphene n-n’ junction as well as the photocarriers’ generation rate due to the linearly polarized radiation of power W. The resulting photovoltage contains polarization angle dependent contribution Vosc which reads

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Here, the factor 0.023 is the single layer absorption, τ=10−12 s is the photocarriers’ life-time [3], λ is the radiation wavelength, vF is the Fermi velocity, ΔU is the built-in potential step, μ is the chemical potential at zero U(x), and θ is the polarization angle. Note, that there is also a term which is independent of θ. Moreover, an irradiated sample experiences heating and, therefore, the electrons are subject to the temperature gradient there. The temperature gradient gives rise to the thermoelectric current flow which is complementary to the photoelectric term. Most important is that the thermoelectric response depends mostly on the radiation power converted to heating and is not sensitive to any particular light polarization. In contrast, the photoelectric response does depend on the polarization angle that makes it possible to separate these two effects in the total response measured. This is schematically shown in Fig. 2. The model considered above allows making the following predictions: (i) The photoelectric contribution in the photoresponse oscillates with the polarization angle θ whereas the thermolelectric one is not sensitive to θ at all. (ii) The amplitude of Vosc increases with the radiation wavelength as λ2. Thus, the photoelectricity may play a major role in the total photoresponse at larger wavelengths. (iii) The amplitude logarithmically depends on the potential step ΔU and increases slowly with ΔU as soon as the later becomes comparable with the initial chemical potential. At the incident radiation power of the order of 100 μW and λ ~ 1000 nm the photovoltage amplitude can be as high as 10 μV .

The model can be generalized for graphene p-n junctions. The photovoltage behavior is qualitatively similar to the one considered above as long as the potential step ΔU is higher than the temperature. We thank Tim Echtermeyer for the stimulating discussions and fresh experimental data [4]. References [1] [2] [3] [4]

S. Mai, S. V. Syzranov, K. B. Efetov, Phys. Rev. B, 83 (2011), 033402. M. Trushin and J. Schliemann, EuroPhys. Lett. 96 (2011), 37006. F. Bonaccorso, Z. Sun, T. Hasan, and A. C. Ferrari, Nat. Photon., 4 (2010), 611. T. Echtermeyer, priv. comm.

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183

Figure 2: Left panel: Relative contributions to the total photoresponse shown schematically. Right panel: The oscillating contribution Vosc given in Volts per Watt as a function of λ computed from the formula given in the main text. The potential step is taken to be equal to the chemical potential.

ABSTRACTS

Figure 1: The pseudospin-dependent selection rule for interband optical excitations in the presence of the electromagnetic radiation polarized along x-axis (zero polarization angle). The potential profile U(x) forming the junction is also shown.

Few-layer graphenes from ball-milling of graphite with triazine derivatives

a,b

Ester Vázquez , Verónica León , Mildred Quintana , Maurizio Prato , M. Antonia Herrero

Departamento de Química Orgánica, Facultad de Ciencias Químicas-IRICA, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain. Department of Chemical and Pharmaceutical Sciences, University of Trieste, Piazzale Europa 1, 34127 Trieste, Italy b

ester.vazquez@uclm.es

Of the different approaches to produce graphene, the solution-phase techniques [1] present several advantages, because stable suspensions of graphene can be used for various processing of the material such as film deposition, surface modification and chemical functionalization, all of which play a crucial role in exploring their applications. The exfoliation of graphene into solution requires breaking the enormous van der Waals-like forces between graphite layers. Molecular adsorption on the surface of graphene is a key step to compensate the attractive interactions between the graphene sheets. [2] Recently, careful calculations have suggested that aminotriazines are strongly adsorbed on graphite. [3] These compounds are particularly attractive, because they offer a combination of unusually strong adsorption and predictable interadsorbate hydrogen bonding which result in the creation of 2D molecular assemblies on graphite. Charge transfer from graphene to aminotriazines seems to occur in part through the presence of hydrogen atoms in the substituents Recently, we have shown that solid phase techniques together with mechanical activation by milling processes can be used to prepare scalable quantities of functionalized carbon nanostructures.[4] Others have used ball milling to solubilize nanotubes through the formation of complexes between carbon nanotubes and various substrates,[5] while wet ball milling (DMF) has produced few layer graphene in solution.[6] All these results suggest that mechanical activation is a very promising way for modifying carbon nanostructures. Herein, we report a simple, practical scalable procedure to produce few-layer graphene sheets using ballmilling Large quantities of inexpensive materials like graphite and melamine can be used for massive and fast production of few layer graphenes with a low concentration of defects. The methodology opens the way for an alternative and efficient processing of graphene materials, such as film deposition and chemical functionalization these fields.

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References [1] [2] [3] [4]

A. A. Green, M. C. Hersam, J. Phys. Chem. Lett., 1, (2010), 544. C. Backes, F. Hauke, A. Hirsch, Adv. Mat., 23, (2011), 2588. J. D. Wuest, A. Rochefort, Chem. Commun., 46, (2010), 2923. N. Rubio, C. Fabbro, M. A. Herrero, A. de la Hoz, M. Meneghetti, J. L. G. Fierro, M. Prato, E. Vazquez, Small, 7, (2011), 665. [5] A. Ikeda, Y. Tanaka, K. Nobusawa and J. Kikuchi, Langmuir, 23, (2007), 10913. [6] W. F. Zhao, M. Fang, F. R. Wu, H. Wu, L. W. Wang, G. H. Chen, J. Mater. Chem., 20, (2010) 5817

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Figure 1: Schematic illustration for the exfoliation of graphite through ball-milling approach

Reconstruction dependent interaction at the Graphene/ 6H-SiC(000-1) interface probed by STM and ab-initio calculations.

J-Y Veuillen, F. Hiebel, P. Mallet, L. Magaud Institut Néel, CNRS-UJF, Boîte Postale 166, 38042 Grenoble, France jean-yves.veuillen@grenoble.cnrs.fr

Graphene single and multilayers grown by thermal decomposition on the 6H(4H)-SiC(000-1) face (in short SiC-C face) have demonstrated physical properties similar to those expected for ideal graphene ([1], see [2] for a review) and thus represent an appealing technique to prepare wafer scale graphene films directly on an insulating substrate. The structure of the interface has a determinant influence on the electronic properties of such samples, as demonstrated in the well documented case of graphene grown on the SiC-Si face: a strong graphene substrate interaction leads to highly perturbed first carbon plane (the so-called buffer layer) which lacks the characteristics Dirac cones of the material, and charge transfer results in a significant doping of the successive graphene planes. Moreover, the interfacial coupling is thought to be responsible for the unique orientation of the carbon planes found in multilayers on the Si face by imposing the orientation of each newly formed graphitic layer. In spite of its relevance, the structure of the interface is not well established for the SiC-C face. Recent reports suggest that it depends on the growth conditions [3], and that it can be heterogeneous [4]. To address this point we have performed Scanning Tunneling Micoscopy (STM) and Spectroscopy (STS) experiments on partially graphitized samples prepared in-situ under UHV, coupled with ab-initio calculations. From an experimental point of view, the so called “transparency” of graphene [5] allows the investigation of the (buried) substrate structure at the interface from high-bias STM images whereas the low energy electronic structure of the graphene layer can be probed in low bias images [6]. Thus a complete description of the electronic structure of the interface can be achieved from variable bias STM/STS data.

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Starting from the clean SiC(3x3) surface, we first obtain monolayer graphene islands on top of the unperturbed SiC(3x3) reconstruction (G/3x3 islands). At variance with the case of the Si face the (azimuthal) orientation of the graphene layer varies from one island to the other, i.e. a “rotational disorder” is found in the samples. No significant perturbations of either the substrate or the graphene layer structures were observed on G/3x3 islands with different orientations [7] (see Figure 1 as an example). This indicates that the graphene-SiC(3x3) interaction is quite weak, leading to an almost ideal system [7]. We shall present STM/STS measurements which allow the determination of parameters (graphene doping and interface defect density) relevant to the physical properties of the system [8]. Finally, owing to the coexistence of G/3x3 islands with area of bare SiC(3x3) surfaces we could perform a quantitative study of the high bias “transparency” of graphene, which indicates an enhancement of the tunnelling probability from/to the substrate surface states when they are buried below the carbon plane [8]. Further annealing below the graphitization temperature leads to the selective transformation below the graphene layer of the SiC(3x3) surface reconstruction into the SiC(2x2) one, leading to G/2x2 islands. This transformation results in an increase of the graphene substrate interaction [9]. The atomic structure of the SiC(2x2) surface is a simple adatom-restatom structure (see Figure 2-a), and the graphene-substrate coupling mostly involves Si adatoms [10]. The lattice mismatch and rotational disorder between graphene and SiC gives rise to moiré patterns [7], and thus the graphene-adatom stacking varies laterally within the

period of the moiré. We shall present STM/STS data which show that the adatom graphene coupling depends on the local configuration, the energy and broadening of the adatom state being different for e.g. top and hollow graphene sites. This result can be qualitatively understood in the framework of a simple (non interacting) Anderson impurity model (see e.g. [11]). This stacking dependent interaction is correlated to perturbations in the low energy local density of states of graphene (see Figure 2-b). Ab-initio calculations allow a quantitative analysis of the full interface electronic structure in the case of small commensurate supercells. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

C. Berger et al. Science 312 (2006) 1191 W. de Heer et al., J. Phys. D: Appl. Phys. 43 (2010) 374007 N. Srivastava, Guowei He, Luxmi, and R. M. Feenstra, Phys. Rev. B 85 (2012) 041404(R) C. Mathieu et al., Phys. Rev. B 83 (2011) 235436 G. M. Rutter et al., Phys. Rev. B 76 (2007) 235416 P. Mallet et al., Phys. Rev. B 76 (2007) 041403(R) F. Hiebel, P. Mallet, L. Magaud, and J.-Y. Veuillen, Phys. Rev. B 80 (2009) 235429 F. Hiebel, L. Magaud, P. Mallet and J-Y Veuillen, to appear in J. Phys. D: Appl. Phys. (2012) F. Hiebel, P. Mallet, F. Varchon, L. Magaud and J-Y Veuillen, Phys. Rev. B 78 (2008) 153412[ L. Magaud, F. Hiebel, F. Varchon, P. Mallet, and J.-Y. Veuillen, Phys. Rev. B 79 (2009)161405(R) T.O. Wehling, M.I. Katsnelson and A.I. Lichtenstein, Chem. Phys. Lett. 476 (2009) 125

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Figure2 : STM images of the same spot on a G/2x2 island, images size: 7.5x7.5 nm². a) High bias image (sample bias: +2.5 V) showing the adatoms of the SiC(2x2) reconstruction through the graphene layer. b) Low bias image (sample bias 50mV) showing the perturbation to the low energy local density of state of graphene in G/2x2 islands. The perturbation leads to “switched-off” graphene atoms (some indicated by arrows), which do not show up in a weakly interacting system (e. g. G/3x3, figure 1-b). The perturbation is modulated in space with the (pseudo) period of the moiré pattern.

ABSTRACTS

Figure 1: STM images of the same spot on a G/3x3 island, images size: 7.5x7.5 nm². a) High bias image (sample bias: -2.0V) showing the structure of the SiC(3x3) reconstruction through the graphene layer. b) Low bias image (sample bias -50mV) showing the low energy features of graphene: honeycomb atomic contrast (left) superimposed to “standing wave patterns” due to electron scattering at the island edge (right).

Cell uptake survey of functionalized Graphene for Near-Infrared Mediated tumor Hyperthermia

M.Vila1,2, M.T.Portolés3, P.A.A.P.Marques4, M.J.Feito3,M.C.Matesanz3,C.Ramírez-Santillán3, G. Gonçalves4, S.M.A. Cruz4, A.Nieto-Peña1,2 and M.Vallet-Regi1,2 1

Inorganic and Bioinorganic Chemistry Dept. Universidad Complutense de Madrid. 28040 Spain Centro de Investigación Biomédica en Red. Bioingeniería, Biomateriales y Nanomedicina, CIBER-BBN 3 Department of Biochemistry and Molecular Biology I, Universidad Complutense Madrid, 28040, Spain, 4 TEMA-NRD, Mechanical Engineering Department, University of Aveiro, 3810-193 Aveiro, Portugal 2

mvila@farm.ucm.es

The exciting advances in the preparation of nanosystems with applications in the medical field have lead to new challenges in the design of smart materials capable of meeting the clinical demands. Therefore, the application of nanotechnology for treatment, diagnosis, monitoring and control of biological systems (recently denominated as nanomedicine) has been declared as one of the most promising fields of research over the last decade. Mainly after finding that the introduction of nanosystems into living cells is possible by shuttling various cargoes across cellular membranes, without producing cytotoxicity. Nanoparticles have been proposed for locally releasing highly toxic drugs directly into tumors, while reducing the unwanted side effects of aggressive treatments, and to target tumors using the intrinsic capacities of different nanomaterials applied as new treatments. For example, their capacity to induce localized heating within tumors is being exhaustively explored. Approaches to nanoparticlemediated thermal therapy include absorption of infrared light, radio frequency ablation, and magnetically-induced heating [1].

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Among carbon based materials, following close and taking over carbon nanotubes, graphene represents one of the most promising “nanoparticle” of the last few years. More specifically, graphene oxide (GO), it is a small two-dimensional shape nanoparticle [2], that offers a new class of solutiondispersible polyaromatic platform for performing chemistry and which aspect ratio make it incomparable to any other previously suggested one. Besides all its properties, its low cost, large production scale and easyprocessing, makes this nanomaterial a promising nanoparticle for medical application were a large scale production is needed. Its unique structure, with all atoms exposed on its surface, has an ultra-high surface area available for efficient loading of aromatic drug molecules, useful for applications in drug delivery. Also, its strong NIR optical absorption ability 700-1100 nm (“therapeutical window”, where it is a non invasive, harmless and skin penetrating irradiation) range is particularly attractive for the induction of cells hyperthermia in tumor treatments as a minimally invasive alternative to surgery (Photothermal therapy). This therapy is based on the transfer of energy produced during the irradiation of a material, after being internalized by a cell, generating vibrational energy, thus generating heat sufficient for cell destruction.[3] With the purpose of understanding the biological response of cells to this graphene uptake, a complete in vitro biocompatibility and internalizing kinetics study of GO sheets has been performed in a survey of different kind of cells: osteoblast, preosteoblasts, fibroblast, and macrophages. GO nanosheets of c.a. 100 nm have been obtained from exfoliation of high purity graphite by a modified Hummers method [4] see Fig. 1, and functionalized in its surface with non-toxic and nonimmunogenic polymers to avoid the intercession with cellular functions or target immunogenicities and to decrease

aggregation. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to measure the thickness and size of the synthesized GO nanosheets. Moreover, the GO particles have been labeled with a fluorescent marker (fluorescein FITC) as this is an important requisite for their in vitro studies with cells both for the application of Confocal Microscopy and Flow Cytometry to follow uptake and possible degradation within cells. Different cell types have been cultured for several incubation periods in the presence of 0.075 mg/mL GO solutions dispersed in supplemented DulbeccoÂ´s Modified Eagle Medium (DMEM). GO-FITC uptake kinetics, cell morphology, viability and proliferation, lactate dehydrogenase release were evaluated in vitro by flow cytometry, and confocal microscopy. Incorporation assays of GO-FITC in the presence of Trypan Blue, in order to quench the extracellular fluorescence, demonstrate the intracellular location of this material. Results show that cell viability measured by propidium iodide exclusion is always above 95% for all the cells type studied after 30, 60 and 150 min and 1 day, suggesting that there is not induction of apoptosis or necrosis by the nanomaterial. As an important discovery, GO uptake kinetics revealed several differences in uptake speed as a function of the type of cell involved. It has been demonstrated that, for example in the case of osteoblast like cells (see Fig.2), uptake kinetics are faster suggesting that GO can more easily penetrate the cell membrane without resulting in greater cell membrane damage. Our studies have clearly demonstrated that the uptake of GO nanosheets by the cells plays an extremely important role in how efficient and controlled the treatments would be, and has given light to the future definition of timing parameters and selective uptake control by certain type of cells in order to achieve an effective therapy. References

[1] [2] [3] [4]

F.A. Jolesz, et al., Cancer J.2002, , 8, S100M. Melucci, et al., J. Mater. Chem. 2010. 20, 9052 Z.M. Markovic et al., Biomaterials 2011,32, 1121 G. GonĂ§alves, et al, Chem. Mater. 2009, 21, 4796

Figure 2: Confocal Microscopy image of osteoblast-like cells (MC3T3). Green fluorescence due to fluorescein labeled GO excitation.

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Figure 1: Scheme of GO exfoliation

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Figures

Defects, Dislocations and Disorder in Graphene at the Atomic Level

R Jamie Warner and Angus Kirkland Department of Materials, University of Oxford, Oxford, UK Jamie.warner@materials.ox.ac.uk

The atomic structure of graphitic nanomaterials can be directly image using high resolution transmission electron microscopy (HRTEM) with spherical aberration correctors (1,2). Using accelerating voltages of 80 kV limits damage to graphene and nanotubes and enables studies of how the atoms are arranged. However, in order to fully resolve the atomic structure of graphene, chromatic aberration effects need to be addressed. I shall present results on defects, dislocations and disorder in graphene obtained with Oxford’s JEOL 2200MCO HRTEM, equipped with probe and image spherical aberration correctors, plus a new double-Wien filter monochromator. The accelerating voltage is reduced to 80 kV, and we can achieve 80 picometer spatial resolution. Using this sub-Angstrom resolution we have resolved several key structures associated with plastic deformation, such as edge dislocations. We have fully resolved 5 and 7 member rings, shown in figure 1, and reveal that C-C bond elongation and compression occurs in specific locations on edge glide dislocations. I will show how we can intentionally create defects and disorder in pristine graphene with an accuracy of 10 nm. Some of these highly strained regions of disorder relax back to pristine graphene, whilst others remain stable. We have also shown that trilayer graphene grown by chemical vapour deposition can adopt ABC stacking. I will present a full analysis of the unique atomic structure of Rhombohedral stacked trilayer graphene. These results demonstrate that improved resolution in HRTEM can enable new insights into the atomic structure of defects, dislocations, disorder, and also the layer stacking in graphene and few layer graphene sheets.

References

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[1] J. H. Warner, M. H. Rümmeli, L. Ge, T. Gemming, B. Montanari, N. M. Harrison, B. Büchner, G. A. D. Briggs, Structural transformations in graphene studied with high spatial and fast temporal resolution, Nature Nanotechnology, 4, p500 (2009) [2] J. H. Warner, N. P. Young, A. I. Kirkland, G. A. D. Briggs, Resolving Strain in Carbon Nanotubes at the Atomic Level, Nature Materials, 10, 958-962, (2011)

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Figure 1: (a) Aberration-corrected HRTEM image (with monochromation of electron beam) of monolayer graphene showing two edge glide dislocations, plus the elastic strain induced in the lattice. (b) Atomic model representation of (a).

Manifestation of electron-electron interaction in the magnetoresistance of graphene 1

2,3

Johannes Jobst , Daniel Waldmann , Igor V. Gornyi , Alexander D. Mirlin 1 Heiko B. Weber

2,4,5

, and

Lehrstuhl für Angewandte Physik, Universität Erlangen-Nürnberg, Erlangen, Germany Institut für Nanotechnologie, Karlsruhe Institute of Technology, Karlsruhe, Germany A.F. Ioffe Physico-Technical Institute, St. Petersburg, Russia 4 Inst. für Theorie der kondensierten Materie, Karlsruhe Institute of Technology, Karlsruhe, Germany 5 Petersburg Nuclear Physics Institute, St. Petersburg, Russia heiko.weber@physik.uni-erlangen.de 2 3

We investigate the magnetotransport in large-area graphene Hall bars epitaxially grown on silicon carbide [1]. In the intermediate field regime between weak localization and Landau quantization the observed temperature-dependent parabolic magnetoresistivity (MR) is a manifestation of the electron-electron interaction (EEI). Using the scattering times gained from a detailed analysis of the weak localization anomaly, we can consistently describe the data with a model for diffusive (magneto)transport. We find excellent agreement between the experimentally observed temperature dependence of MR and the theory of EEI in the diffusive regime. We can further assign a temperature-driven crossover to the reduction of the multiplet modes contributing to EEI from 7 to 3 due to intervalley scattering. In addition, we find a temperature independent ballistic contribution to the MR in classically strong magnetic fields. The compelling similarity of recent experiments [2] (which were attributed to Kondo physics) to the wellcontrolled corrections due to EEI is critically discussed. References [1] J. Jobst, D. Waldmann, I. V. Gornyi, A. D. Mirlin, and H. B. Weber: arXiv:1110.5893v2, accepted for publication in Phys. Rev. Lett. [2] J.-H. Chen, L. Li, W.G. Cullen, E. D. Williams, and M. S. Fuhrer, Nature Physics 7, (2011) 535–538

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ABSTRACTS

Figures

Figure 1: a The magnetoresistivity displays a parabolic magnetic field dependence in between the weak localization and the Landau quantization regime. Its temperature dependent part is caused by electron-electron interaction. A detailed analysis displays a consistent description of the purely diffusive regime at not too high fields, and b a graphene-specific crossover to a higher number of contributing multiplet channels. Further, a crossover in strong magnetic fields (|B|>5T) is observed.

Modeling Electronic Properties of Single-layer and Multilayer Graphene

Shengjun Yuan, Mikhail I. Katsnelson Institute for Molecules and Materials, Radboud University of Nijmegen, NL-6525AJ Nijmegen, The Netherlands s.yuan@science.ru.nl

Recent experimental realizations of bilayer and trilayer graphene have opened the possibility of exploring their intriguing electronic properties, which depend dramatically on the stacking sequence of the graphene layers. It has been demonstrated that the band gap can be tuned from 0 to several hundred meV by applying voltage to a dual-gate bilayer or ABC-stacked trilayer graphene field-effect transistor (FET) at room temperature. These experimental observations are important for the applications of graphene in future electronics. Just like the single-layer graphene, the bilayer and trilayer graphene samples in the real experiments always have different kinds of disorder or impurities, such as ripples, adatoms, admolecules, etc. One of the most important problems in graphene physics is to understand the effect of these imperfections on the electronic structure and transport properties, especially for the cases of gap opening under the perpendicular electronic field. Motivated by recent experiments, we performed a systemic study of the effects of different types of disorder or impurities to the electronic properties of single-layer and (gated or ungated) multilayer (including bilayer and trilayer) graphene [1-9].

193

ABSTRACTS

We study this issue by direct numerical simulations of electrons on a honeycomb lattice in the framework of full pi-band tight-binding model. The magnetic field is introduced by means of the Peierls substitution. Numerical calculations based on exact diagonalization can only treat samples with relative small number of sites. For large graphene sheet with millions of atoms, the numerical calculation of an important property, the density of states (DOS), is performed by the time-evolution method. The time-evolution method is based on numerical solution of time-dependent Schrรถdinger equation with additional averaging over random superposition of basis states. We further extend this method to the calculation of various quantities by using the Kubo formula, such as the static and dynamical conductivity, polarization function, dielectric function, response function, and energy loss function. The effect of electron-electron interaction is considered within the random phase approximation (RPA). Another extension of the time-evolution method yields the quasieigenstate, a superposition of degenerate energy eigenstates. The Klein tunneling and quantum interference (Aharonov-Bohm effect) are studied by direct simulation of the wave packet propagation. Our numerical method allow us to carry out calculations for rather large systems, up to hundreds of millions of sites, with a computational effort that increases only linearly with the system size.

References S. Yuan, H. De Raedt, and M. I. Katsnelson, Phys. Rev. B, 82 (2010) 115448. S. Yuan, H. De Raedt, and M. I. Katsnelson, Phys. Rev. B, 82 (2010) 235409. S. Yuan, R. Roldรกn, and M. I. Katsnelson, Phys. Rev. B, 84 (2011) 035439. S. Yuan, R. Roldรกn, and M. I. Katsnelson, Phys. Rev. B, 84 (2011) 125455. S. Yuan, R. Roldรกn, H. De Raedt, and M. I. Katsnelson, Phys. Rev. B, 84 (2011) 195418. T. O. Wehling, S. Yuan, A. I. Lichtenstein, A. K. Geim and M. I. Katsnelson, Phys. Rev. Lett., 105 (2010) 056802. R. R. Nair, W. C. Ren, R. Jalil, I. Riaz, V. G. Kravets, L. Britnell, P. Blake, F. Schedin, A. S. Mayorov, S. Yuan, M. I. Katsnelson, H. M. Cheng, W. Strupinski, L. G. Bulusheva, A. V. Okotrub, I. V. Grigorieva, A. N. Grigorenko, K. S. Novoselov, A. K. Geim, Small, 6 (2010) 2877. [8] A. Singha, M. Gibertini, B. Karmakar, S. Yuan, M. Polini, G. Vignale, M.I. Katsnelson, A. Pinczuk, L.N. Pfeiffer, K.W. West, and V. Pellegrini, Science, 332 (2011) 1176. [9] S. Yuan, R. Roldรกn, and M. I. Katsnelson, arXiv:1201.4454

194

ABSTRACTS

[1] [2] [3] [4] [5] [6] [7]

Tri-layer enriched graphene sample by mechanochemical exfoliation of graphite: A one-step route for the production, processing and deposition as transparent films. 1

Aldo J.G. Zarbin , Rodrigo V. Salvatierra , Sergio H. Domingues , Marcela M. Oliveira

Department of Chemistry, Federal University of Paranรก (UFPR), Curitiba-PR, Brazil. Department of Chemistry and Biology, Technological Federal University of Paranรก (UTFPR), Curitiba-PR, Brazil.

aldozarbin@ufpr.br

Several efforts have been made in the last few years to produce graphene with yields high enough to be viable for scalable manufacturing. The majority of these efforts, however, resulted in graphene that was lacking in structural integrity or yield or purity. Besides the search for efficient bulk production methods for high-quality graphene samples, there are other important challenges in the field: one of them is related to the development of efficient processing routes to graphene. Graphene is a promising candidate for the next-generation opto-electronic devices, and these types of applications require the fabrication of largescale, transparent thin films of graphene onto a number of different types of substrates, including plastics, flexible and stretchable substrates. Another challenge is the development of synthetic routes to produce size- and layer-monodispersed graphene. We report here a novel route for the production of trilayer enriched graphene samples, obtained from graphite flakes, in which both the synthesis and processing as a transparent thin film (easily transferred to arbitrary substrates) are solved together in one single pot. The starting material should be any type of graphite sample, onto which a mechanical exfoliation processes are performed, followed by chemical/thermal exfoliation, yielding few-layer graphene (FLG) flakes. The chemical/thermal exfoliation is performed in a water/oil biphasic system in which the resulting FLG spontaneously self-assembles at the water/oil interface as a thin film that is easily transferred to an arbitrary substrate. The whole process consists in a mechanical peeling of graphite by rubbing it on the surface of a magnesium foil. The magnesium holding the peeled graphite is subsequently mixed to a heterogeneous liquid-liquid mixture formed from a toluene/aqueous hydrochloric acid solution under a ultrasonic bath. Immediately after the contact with the aqueous acid solution, the magnesium foil dissolves through a highly exothermic reaction. The carbonaceous material (characterized as FLG) remains dispersed in the water/toluene emulsion, and spontaneously agglomerates into a continuous and homogenous film located at the toluene/water interface, that can be easily transferred to an arbitrary substrate.

195

The authors acknowledge the financial support of CNPq, NENNAM (Pronex-F.Araucรกria/CNPq), Brazilian Network on Carbon Nanotubes Research (CNPq) and the National Institute of Science and Technology of Carbon Nanomaterials (INCT-Nanocarbono). We also thank LME-UFPR for the TEM images. RVS and SHD thanks CNPq for the fellowship.

ABSTRACTS

Figure 1a shows films deposited onto glass substrates (upper) and plastic substrates (bottom). The flexibility of the film on plastic substrate can be seen in Figure 1b. The film presents excellent optical transparencies (90% at 550 nm). The occurrence of FLG was confirmed by TEM, Electron Difraction and Raman spectroscopy. By analyzing 100 Raman spectra collected at different samples we generate occurrence statistics and estimate that our sample is composed of 59% of tri-layer AB-stacked graphene, which is one of the most efficient layer-controlled syntheses of tri-layer FLG described to date.

Figures

196

ABSTRACTS

Figure 1: A photograph of transparent graphene films deposited on quartz substrates (upper) and plastic (PET) substrates (bottom). For the quartz substrate from the left to the right it is shown the substrate itself (with no film deposited), and films prepared with 5 cm (middle) or 10 cm (right) of graphene. For the plastic substrate from the left to the right it is shown the substrate itself (with no film deposited) and a film deposited starting from 5 cm of magnesium foil. (b) A picture of the flexibility of the graphene film on the PET substrate.

Selective generation of Dirac-Fermi polarons at graphene edges and atomic vacancies

Xi Zhang, Changqing Sun School of Electric & Electronic Engineering, Nanyang Technological Univeristy, Singapore zh0005xi@e.ntu.edu.sg

The generation and hydrogen modulation of the massless[1], magnetic[2], and mobile Dirac-Fermi polarons (DFPs) surrounding atomic vacancies at graphite surface and at edges of graphene nanoribbons (GNR) are indeed fascinating with mechanisms far from clear. Here we show that an incorporation of the bond order-length-strength (BOLS) correlation[3] into the spin-polarized tight-binding (TB) method with the combination of the density-functional theory calculations have enabled the clarification of the concerns. We found that: i) the DFPs with high-spin-density at the zigzag-GNR and at the vacancies result from the isolation and polarization of the dangling -bond electrons of identical distance along the edges by the under-coordination-induced local densification and quantum entrapment of the core and bonding electrons; ii) the pseudo-π-bond formation between the nearest dangling σ-bond electrons along the armchair-GNR and the reconstructed-zigzag-GNR edges prevents, however, DFPs from being formed at these edges; and, iii) hydrogenation reduces the spin density substantially and turns the asymmetric dumb-bell-like sp2 into the spherical-like pz charge density of the zigzag-GNR edge and vacancy. A further photoelectron spectroscopic purification[4] has confirmed the origin and consequence of the DFPs generated at graphite surface atomic vacancies.

References

ABSTRACTS

Soldano, C., A. Mahmood, and E. Dujardin, Carbon, 8(2010), 2127-2150. Cervenka, J., M.I. Katsnelson, and C.F.J. Flipse, Nature Phys., 11(2009), 840-844. Zhang, X., et al., Nanoscale, (2010), 2160-2163. Sun, C.Q., Nanoscale. 10(2010), 1930-61.

197

[1] [2] [3] [4]

Figures

198

ABSTRACTS

Figure 1: Comparison of the purified XPS C 1s spectrum of graphite surface with and without vacancy defects showing that bonds near to defects are shorter and stronger than those at the surface. The P, TS, and TD denotes, respectively, the DFPs screened, undercoordination-induced quantum entrapment states of the outermost two atomic layers of surface skin (z~ 3.2) and sites surrounding vacancy defects (z~ 2.5); D and B indicates the bulk position of diamond (z =12) and graphite (z = 5.335). The valleys centered at 284.2(z = 5.35) and 284.4 eV(z = 4) correspond, respectively, to the removed obvious graphite bulk and surface information. Indicated numbers are the effective z values.

Figure 2: Comparison of the DFT-derived local spin-density contour and the BOLS-TB derived 3D plots of local spin density of occupied states for (a) vacAGNR, (b) H-vacAGNR, (c) ZGNR, (d) H-ZGNR. The Dx (x = a, v, r, z) represents the dangling sp2 electron states indicated using red arrows. The dangling sp2 and the pz electron, contributes to a strong dumbbell-shaped local antiferromagnetism and a weak spherical spin, respectively. The sites of group I show a much higher spin density 2 than group II. Hydrogenation tends more to interact and pair up the dangling sp electron than the pz electrons.

Graphene films synthesized via CVD

A. Zurutuza Graphenea, San Sebastian, Spain

Graphene seems to be the new wonder material and as such could be potentially applied in many different fields. Depending on the application the graphene format can vary from powder/flake to homogeneous film form. The powder form could meet large volume/weight requirements and can be obtained from graphite. While the large area graphene films can be obtained using chemical vapor deposition (CVD) methods on a metal catalyst such as copper [1]. The synthesis of the graphene film is only the first step since it has to be typically transferred onto insulating or similar substrates for subsequent characterization or device fabrication. The importance of this transfer process is usually underestimated and if not done with care it can end up damaging the graphene and in turn its performance. The synthesis of graphene films via CVD will be described. After a successful transfer of monolayer and bilayer graphene films onto the required substrates; the characterization via Raman, high resolution and scanning mode TEM will be presented. Suspended graphene samples were required in order to determine the grain diffraction pattern [2], the number of graphene layers and the orientation/stacking between the different layers [3,4] using TEM. Even if the preparation of suspended graphene samples is not straightforward the amount of information that can be extracted from this characterization technique is extremely valuable.

References

ABSTRACTS

X. Li, et al Science 324, 1312 (2009). P.Y. Huang et al Nature 454, 390 (2011). H.J. Park et al Carbon 48, 1088 (2010). J.C. Meyer et al Solid State Commun. 143, 101 (2007).

199

[3] [4] [5] [6]

POSTERS

Posters - Alphabetical Order (187)

Only Posters submitted by registered participants are listed below. Last update (16/03/2012) (Please, find your final poster number by looking up your name in the Author Index displayed in the Registration and the Poster Exhibition Areas)

Italy

Topic

Poster Title

Student Senior

Growth, synthesis techniques and integration methods Growth, synthesis techniques and integration methods

Studies of Isocyanate oligomer mixed with Graphene Oxide

Student

CVD grown graphene evaluated with Raman and optical microscope

Student

Other 2 dimensional materials

AFM-studies of humidity dependence of friction in graphene and other 2D materials

Agalou

Konstantinos

Ahlberg

Patrik

Sweden

Ahlskog

Markus

Finland

Alekseyev

Nick

Russia

Alexeev

Arseny

United Kingdom

Quantum transport

Two-phonon scattering in graphene in the quantum Hall regime

Student

Alonso Pruneda

Miguel

Spain

Other 2 dimensional materials

Magnetoelectric and Flexomagnetic effects in hybrid C/BN nanostructures

Senior

Alvarez

Patricia

Spain

Chemistry of Graphene

Different chemical approaches to produce graphene derivatives

Senior

Antonova

Irina

Russia

Antonova

Irina

Russia

Chemistry of Graphene

Archambault

ChloĂŠ

Canada

Chemistry of Graphene

Arzac

Alejandro

Spain

Bacsa

Revathi

France

Chemistry of Graphene

Baker

Jenny

United Kingdom

Chemistry of Graphene

Baldwin

Jack

United Kingdom

Growth, synthesis Computer Simulation of Epitaxial Graphene techniques and integration Assembly on Silicon Carbide Surface with Using methods Semi-Empirical Quantum Chemistry Methods

Applications (gaz sensors, Advantage of few-layer graphene in comparison composites, nanoelectronic with graphene for applications devices...) Fluorographene with nanoswell surface relief obtained by hydrofluoric acid treatment Charge transfer engineering in graphene nanoribbons using metallic contacts and organic adsorbed layers

Senior

Student

Applications (gaz sensors, Emulsion mixing technique for preparation of Student composites, nanoelectronic poly(buthylacrylate/methylmethacrylate)/graphe devices...) ne electrically conductive composite films

Quantum transport

Few layer graphene decorated with Pd nanoparticles: synthesis, characterisation and catalytic applications in the electrochemical oxidation of alcohols Development of a technique based on methylene blue for characterizing specific surface area of graphenes and other carbon nanostructures A generalised, tight-binding transport model description for random edge-defected ZGNRs

Senior

Student

POSTERS

Country

203

Presenting Author

204

POSTERS

Presenting Author

Country

Topic

Poster Title

Growth, synthesis Graphene research in Lithuania with subsequent techniques and integration application in bioanalysis, energy storage and methods optical materials

Student Senior

Barkauskas

Jurgis

Lithuania

Bayer

Bernhard

United Kingdom

Growth, synthesis In-situ Characterization of Graphene Growth techniques and integration methods

Bending

Simon

United Kingdom

Quantum transport

Bergmair

Iris

Austria

Bergonzo

Philippe

France

Bhandari

Sagar

Bianco

Giuseppe Valerio

Bin Hashim

Abdul Manaf

Blaszczyk

Jan

Poland

Boscá

Alberto

Spain

Boukhicha

Mohamed

France

Other 2 dimensional materials

Raman scattering in single layer MoS2: Phonon Bandwidths, zone edge phonons and 2D effects

Student

Bukhvalov

Danil

Korea

Chemistry of Graphene

Catalytic properties of imperfect graphene: first principles modeling

Senior

Bundesmann

Jan

Quantum transport

Spin relaxation in graphene induced by adatoms

Student

Bustero

Izaskun

Spain

Candini

Andrea

Italy

Ceccato

Marcel

Denmark

Celik

Yasemin

Turkey

Chen

Sweden

Chernozatonskii

Leonid

Growth, synthesis Large area Micro- and Nanostructuring of techniques and integration Graphene methods Applications (gaz sensors, Assembling graphene with diamond as novel composites, nanoelectronic platforms for biointerfacing and photovoltaics devices...)

United States Spectrocopies and microscopies Italy

Malaysia

Germany

Russia

Superconductivity in Two-dimensional Crystals

Chemistry of Graphene

Plasmonic gold nanoparticle deposition on pristine and functionalized graphene

Interaction of epitaxial graphene with SiC substrate studied by Raman spectroscopy

Applications (gaz sensors, Ambient p-doping of CVD graphene composites, nanoelectronic devices...)

Applications (gaz sensors, Improvement of thermal conductivity in graphene composites, nanoelectronic reinforced cyanate ester resin devices...) Magnetism and Spintronics Hybrid Graphene – Molecular Magnet Devices for Spintronics Chemistry of Graphene

Senior

Direct Imaging of atomic scale ripples in few-layer Student graphene

Applications (gaz sensors, Gate Control of Nonlinear Characteristics in composites, nanoelectronic Chemically Doped Graphene Three-Branch devices...) Junction Device Spectrocopies and microscopies

Senior

Insights into the chemical modification of graphene using diazonium salts

Senior

Student

Senior

Senior Senior

Growth, synthesis Preparation of Graphene Sheets from Expandable Student techniques and integration Graphite and Their Utilization in Ceramic-Matrix methods Composites Applications (gaz sensors, Field-Effect Sensor Based on Graphene Thin Films composites, nanoelectronic Fabricated by Layer-by-Layer Stacking devices...) Applications (gaz sensors, Formation of quantum dots by "landing" of composites, nanoelectronic hydrogen atoms on graphene nanoribbons – devices...) modeling of process, structures and properties

Student

Senior

Topic

Poster Title

Student Senior

Chshiev

Mairbek

France

Magnetism and Spintronics Magnetic insulator proximity induced spinpolarization in graphene

Senior

Ciuk

Tymoteusz

Poland

Magnetism and Spintronics Contactless magnetoresistance in large area CVD graphene grown on SiC substrates

Student

Connolly

Malcolm

Quantum transport

Quantized Charge Pumping in Graphene

Senior

Crassee

Iris

Intrinsic terahertz magnetoplasmons in monolayer graphene

Student

Cruz

Sandra

Portugal

Spectrocopies and microscopies

Synthesis of graphene-based nanocomposites as SERS substrates in biodetection

Student

Dabrowski

Pawel

Poland

Spectrocopies and microscopies

Scanning tunnelling spectroscopy investigations of Senior chemical composition of graphene/Cu(111) interface

Declerck

Xavier

Belgium

Spectrocopies and microscopies

Boron and nitrogen doping from first principles

Student

Dollfus

Philippe

France

Quantum transport

Effect of negative differential conductance in graphene Esaki diodes: GNR or GNM?

Senior

Downing

Charles

United Kingdom

Quantum transport

Zero-energy states in graphene waveguides, quantum dots and rings

Student

Drexler

Christoph

Germany

Spectrocopies and microscopies

Terahertz Radiation Induced Edge Currents in Graphene

Student

Ellis

Amanda

Australia

Chemistry of Graphene

Graphene Oxide Flower-like Microstructures from Carbon Nanotubes

Senior

Erts

Donats

Latvia

Nanoelectromechanical systems

Application of Ge nanowire mass sensor for graphene exfoliation

Senior

Fedor

Tkatschenko

Quantum transport

Superlattice Effects on Transport in Graphene and Student Graphene Nanoribbons

Fujii

Takeshi

Japan

Gajewski

Krzysztof

Poland

Gao

Jianhua

Japan

Garcia-Gallastegui Ainara

United Kingdom

Switzerland Spectrocopies and microscopies

Germany

United Kingdom

Gaudreau

Louis

Spain

Gholamvand

Zahra

Ireland

Giardi

Rossella

Italy

Growth, synthesis Cu(111) epitaxial films on mica(001) substrate techniques and integration used for high quality graphene growth by methods chemical vapor deposition Spectrocopies and microscopies

SPM investigations of electrical properties of graphene nanostructures on 6H-SiC substrate

Growth, synthesis Epitaxial Growth of Single- and Few-layer techniques and integration Graphene on Pt(111) and Pd(111) Surfaces by methods Surface Segregation Applications (gaz sensors, Graphene Oxide supported Layered Double composites, nanoelectronic Hydroxides for CO2 capture applications devices...) Applications (gaz sensors, Hybrid graphene-quantum dot phototransistors composites, nanoelectronic with ultrahigh gain devices...)

Senior

Student

Senior

Applications (gaz sensors, Hydrothermal synthesis of TiO2 composites, nanoelectronic nanotube/Graphene oxide composite and its Student devices...) application in photocatalytic purification of water Applications (gaz sensors, Simultaneous in-situ graphene oxide reduction composites, nanoelectronic and UV curing of acrylic based formulations for devices...) inkjet printing.

Student

POSTERS

Country

205

Presenting Author

206

POSTERS

Presenting Author

Country

Topic

Poster Title

Growth, synthesis Self-assembly of a sulphur-terminated graphene techniques and integration nanoribbon within a single-walled carbon methods nanotube.

Student Senior

Gimenez Lopez

Maria del Carmen

United Kingdom

Goncalves

Gil

Portugal

Goor Pedersen

Jesper

Denmark

Grodecki

Kacper

Poland

Güryel

Songül

Belgium

Hague

James

Hajgato

Balazs

Han

Chang-Soo

Hancock

Yvette

United Kingdom

Magnetism and Spintronics Towards a realistic model of nanographene linking theory and experiment

Senior

Henrard

Luc

Belgium

Spectrocopies and microscopies

Senior

Hesse

Lisa

Germany

Magnetism and Spintronics Orbital Magnetism in graphene bulk and nanostructures

Student

Heydrich

Stefanie

Germany

Spectrocopies and microscopies

Photoluminescence in Graphene Antidot lattices

Student

Hong

Seul Ki

Chemistry of Graphene

Chemical Analysis and Thermal Curing Effects of CVD graphene during Transfer Pocess

Student

Hussein

Laith

Germany

Huynh

Chi

Australia

Ijäs

Mari

Finland

Ilie

Adelina

Isic

Senior

Applications (gaz sensors, New bioactive PMMA-Hydroxyapatite based bone Student composites, nanoelectronic cement reinforced with graphene oxide devices...) Magnetism and Spintronics Magneto-Optical Properties of Antidot Lattices

Senior

Spectrocopies and microscopies

Graphene formation on SiC (0001) surface steps by CVD process

Student

Nanoelectromechanical systems

Influence of Structural Defects and Chemical Student Functionalisation on the Mechanical Properties of Graphene

United Kingdom

Quantum transport

Gap engineering in atomically thin materials

Senior

Belgium

Nanoelectromechanical systems

Computation of Intrinsic Mechanical Properties of Double Layer Graphene

Senior

Korea

Chemistry of Graphene

Direct transfer of graphene without the removal of a metal substrate using a liquid polymer

Korea

Electronic properties and STM images of N and B doped graphene

Applications (gaz sensors, Decorated Carbon Nanostructured Electrodes for composites, nanoelectronic Biofuel Cell applications devices...)

Senior

Student

Growth, synthesis Structured Graphene – Spinnable CNT and Beyond Student techniques and integration methods Chemistry of Graphene

Chemical modification of graphene with Cl

Student

United Kingdom

Spectrocopies and microscopies

Surface Potential Variations in Graphene Induced by Crystalline Ionic Substrates

Senior

Goran

Serbia

Spectrocopies and microscopies

Plasmonic resonances in the infrared spectra of nanostructured graphene

Senior

Jackman

Richard

United Kingdom

Jeong

Seung Yol

Korea

Growth, synthesis Diamond as a platform for supporting graphene techniques and integration methods Chemistry of Graphene

Highly Concentrated and Conductive Reduced Graphene Oxide Nanosheets by Monovalent Cation-pi interaction: Toward Printed Electronics

Senior

Spain

Topic

Poster Title

Applications (gaz sensors, Prospects of Graphene-enabled Wireless composites, nanoelectronic Communications devices...)

Student Senior

Jornet

Josep Miquel

Joucken

Frederic

Belgium

Spectrocopies and microscopies

Localized state and charge transfer in nitrogendoped epitaxial graphene

Student

Kaestner

Bernd

Germany

Quantum transport

Nanoscale dual-gating of bilayer graphene on GaAs substrates

Senior

Kam

Kendra Fong Yu

Singapore Chemistry of Graphene

Kang

Hong Seok

Kayhan

Emine

Germany

Kim

HoKwon

United Kingdom

Klarskov

Mikkel

Denmark

Kochmann

Sven

Germany

Spectrocopies and microscopies

The Fluorescence Properties of Graphene Oxide

Student

Koghee

Selma

Belgium

Other 2 dimensional materials

Merging and alignment of Dirac points in a shaken honeycomb optical lattice

Student

Kumar

Bijandra

France

Kusmartsev

Feodor

United Kingdom

Landers

John

Laszlo

Istvan

Hungary

Laursen

Bo W.

Denmark

Lazar

Petr

Czech Republic

Chemistry of Graphene

Nature of Interaction of Graphene with Ag, Au, Pd Metals

Senior

Leconte

Nicolas

Belgium

Quantum transport

Chemically Tunable Transport Phenomena of Functionalized Graphene

Student

Lee

Gun-Do

Korea

Quantum transport

Student

Influence of Graphite Defect Density on Oxidation Student Behavior and Pi-electron Topology of Substoichiometric Graphene Oxides Quantum Transport through Heterobilayers of Graphene Nanoribbon and Porphyrin Tape

Applications (gaz sensors, Synthesis, Characterization and Gas Sensing composites, nanoelectronic Behaviour of Large Area Continuous and Transparent Graphene Films by Chemical Vapor devices...) Deposition Growth, synthesis Nucleation and growth mechanism of graphene techniques and integration on copper methods Applications (gaz sensors, Micro four-point probe characterization of composites, nanoelectronic nanostructured graphene devices...)

Senior

Student

Growth, synthesis Epitaxial Graphene on Si face of SiC: A Senior techniques and integration Comparative Study of Different Growth Conditions methods Spectrocopies and microscopies

United States Chemistry of Graphene

A Stable â&#x20AC;&#x153;Flat? Form of Two-Dimensional Crystals: Could Graphene, Silicene, Germanene Be Minigap Semiconductors and Have Huge Magnetoresistance?? Investigation of Alumina/Graphene Oxide role in catalysis

Growth, synthesis Molecular dynamics simulation of carbon techniques and integration nanostructures methods Applications (gaz sensors, Graphene Oxide as a Mono Atomic Protection composites, nanoelectronic Layer for Molecular Electronics: A Quantative devices...) Structural Study

Growth, synthesis Atomistic Processes of Grain Boundary Motion techniques and integration and Annihilation in Graphene methods

Senior

Student

Senior

POSTERS

Country

207

Presenting Author

POSTERS

Korea

Topic Spectrocopies and microscopies

Poster Title Estimation of Youngâ&#x20AC;&#x2122;s Modulus by Raman Spectroscopy on Biaxially Strained Graphene

Student Senior

Lee

Jae-Ung

Lenz

Lucia

Germany

Magnetism and Spintronics Graphene with a spin-orbit super-lattice potential Student

Lenzer

Thomas

Germany

Spectrocopies and microscopies

Tao

Denmark

Qiang

Denmark

Nanoelectromechanical systems

Suspended Graphene Based Devices and Nanomechanical Properties

Student

Lindvall

Niclas

Sweden

Nanoelectromechanical systems

Towards transfer-free fabrication of graphene NEMS

Student

Lipinska

Ludwika

Poland

Chemistry of Graphene

Fabrication of graphene flakes via oxidationreduction method

Senior

Lissowski

Andrzej

Poland

Liu

Ming-Hao

Germany

Quantum transport

Minimal Tight-Binding Model for Quantum Transport in Graphene Heterojunctions

Senior

Lofwander

Tomas

Sweden

Quantum transport

Graphene nanogap for gate-tunable quantumcoherent single-molecule electronics

Senior

Lopes

J. Marcelo

Germany

Lopez-Polin

Guillermo

Spain

Martin-Martinez Francisco

208

Country

Ultrafast transient absorption and Ramanimaging studies of stacked graphene

Applications (gaz sensors, Solution-Processed Ultrathin Chemically Derived composites, nanoelectronic Graphene Films as Soft Top Contacts for Soliddevices...) State Molecular Electronic Junctions

Growth, synthesis Modelling graphene growth by atomistic techniques and integration simulation of 2D polycrystal crystallization â&#x20AC;&#x201C; video methods

Growth, synthesis Synthesis of nanocrystalline graphene on techniques and integration Al2O3(0001) by molecular beam epitaxy methods

Student

Senior

Spectrocopies and microscopies

Measurement of reduced graphene oxide conductivity using Electrostatic Force Microscopy

Belgium

Chemistry of Graphene

Edge functionalization of graphene nanoribbons for electronic applications

Senior

Student

Mathieu

Claire

France

Spectrocopies and microscopies

Effect of Oxygen Adsorption on the Local Properties of Epitaxial Graphene on SiC

Senior

Matkovic

Aleksandar

Serbia

Spectrocopies and microscopies

Spectroscopic ellipsometry measurements of doped graphene

Student

Mazur

Jacek

Poland

Mehr

Wolfgang

Michon

Adrien

Mohamadi

Somayeh

Germany

France

Germany

Applications (gaz sensors, Application of multilayer graphene for composites, nanoelectronic modification of the properties of composite devices...) materials Applications (gaz sensors, Complementary hot carrier transistor with vertical composites, nanoelectronic graphene base electrode for THz applications devices...) Growth, synthesis Structure and interface of graphene films grown techniques and integration on SiC using propane-hydrogen-argon CVD methods Applications (gaz sensors, Surface Modification of Graphene Thorough composites, nanoelectronic Controlled Radical and Conventional Free Radical devices...) Polymerization

Senior

Student

Ana

Brazil

Topic Chemistry of Graphene

Poster Title

Removal of oxidation debris from graphene oxide: Student influence on the formation of composites based on silver nanoparticles

Applications (gaz sensors, Optical biosensors based on graphene composites, nanoelectronic devices...)

Morales-Narvรกez Eden

Spain

Munarriz

Javier

Spain

Muramatsu

Kazuo

Japan

Nanjundan

Ashok

France

Chemistry of Graphene

Neek-Amal

Mehdi

Iran

Nanoelectromechanical systems

Nesladek

Milos

Belgium

Neuen

Christian

Germany

Zhenhua

China

Nicholas

Robin

United Kingdom

Nogaret

Alain

United Kingdom

Applications (gaz sensors, Tunneling Negative Differential Resistance in composites, nanoelectronic Flexible Silicone/Graphite Composites devices...)

Oroszlany

Laszlo

Hungary

Quantum transport

Intraband electron focusing by a flat lens in bilayer graphene

Osella

Silvio

Belgium

Spectrocopies and microscopies

Graphene nanoribbons as low-bandgap donor materials for organic photovoltaic: Quantumchemical aided design

Paiva

Maria

Portugal

Chemistry of Graphene

Formation of Graphene Nanoribbons in Solution

Parvez

Md Khaled

Germany

Pasternak

Iwona

Poland

Peressi

Maria

Italy

Quantum transport

Student Senior

Student

Spin-dependent negative differential resistance in Student graphene superlattices

Development and Study of manufacturing method Growth, synthesis Senior techniques and integration of few layers graphene dispersed solution for wet methods coating Facile synthesis of high quality metal free reduced graphene nanosheets from expandable graphite oxide Effect of grain boundary on the buckling of graphene nanoribbons

Growth, synthesis Low Temperature Graphene Growth Using Large techniques and integration Area Linear-Antenna Microwave Plasma methods Enhanced CVD System

Senior

Chemistry of Graphene

Effects of nanostructures on macroscopic physical Student properties of graphene layers

Spectrocopies and microscopies

Surface enhanced Raman scattering of graphene

Quantum transport

Senior

Energy loss rates of hot Dirac fermions in Senior epitaxial, exfoliated and CVD graphene under high magnetic fields Senior

Senior

Student

Senior

Applications (gaz sensors, Nitrogen-doped Graphene and its Iron-based Student composites, nanoelectronic composite as Efficient Electrocatalysts for Oxygen devices...) Reduction Reaction Growth, synthesis Graphene growth on Cu mono- and techniques and integration polycrystalline substrates methods Chemistry of Graphene

Hydroxyl Functional Groups on Pristine, Defected Graphene, and Graphene Epoxide: insights from first principles calculations

Senior

POSTERS

Moraes

Country

209

Presenting Author

210

POSTERS

Presenting Author

Country Denmark

Topic

High Conductance, Large Area, Single Layer Graphenes from Graphene Oxide

Student Senior

Petersen

Soren

Pignedoli

Carlo Antonio

Poltierova Vejpravova

Jana

Popov

Andrei

Prezzi

Deborah

Rioux

Julien

Romeo

Valentina

Rozhkova

Natalia

Rudenko

Alexander

Ruiz

Virginia

Sachs

Burkhard

Germany

Chemistry of Graphene

Samuels

Alexander

United Kingdom

Applications (gaz sensors, Organic and Metallo-organic Doping of Graphene Student composites, nanoelectronic devices...)

Sandana

Eric Vinod

France

Sandhu

Adarsh

Japan

Santos

Cristiane

Saxena

Manav

Schellenberg

Peter

Schlierf

Andrea

Italy

Schopfer

Félicien

France

Switzerland

Czech Republic Russia Italy Germany

Chemistry of Graphene

Poster Title

Growth, synthesis Graphene Nanoribbon Heterojunctions via partial techniques and integration cyclodehydrogenation methods Magnetism and Spintronics Magnetic and transport properties of graphene@MNPs hybrides

Student

Senior

Chemistry of Graphene

Chiral graphene nanoribbon inside carbon nanotube: ab initio study

Senior

Spectrocopies and microscopies

Structure, Stability and Electronic Properties of Graphene Edges on Co(0001)

Senior

Magnetism and Spintronics Optical spin current injection in graphene

Senior

Italy

Chemistry of Graphene

Mechanical stabilization of graphene aerogels by vulcanization with pure sulphur

Senior

Russia

Chemistry of Graphene

Molecular graphene of shungite

Senior

Germany

Chemistry of Graphene

Adsorption of cobalt on graphene: a quantum chemical perspective

Senior

Spain

Belgium India

Portugal

Growth, synthesis Graphene produced by electrochemical exfoliation Senior techniques and integration of graphite: electroanalytical properties methods Theory of graphene-boron nitride heterostructures

Growth, synthesis Synthesis of conducting transparent few-layer techniques and integration graphene directly on Glass at 450°C methods Growth, synthesis Ecofriendly Reduction of Graphene Oxide Using techniques and integration Extremophile Bacteria methods

Student

Senior

Spectrocopies and microscopies

Reflectance of pristine and N-doped epitaxial graphene from THz to mid-IR

Chemistry of Graphene

Graphene: In Our Food Stuffs since Mesolithic Age Student

Growth, synthesis Efficient graphene preparation by combined techniques and integration intercalation – exfoliation steps methods Chemistry of Graphene

Quantum transport

The interaction of pyrene derivatives with graphene nanoplatelets Quantum Hall effect in exfoliated graphene affected by charged impurities: metrological measurements

Senior

Student

Senior

Country

Shylau

Artsem

Sweden

Quantum transport

Silva-Guillén

Jose Angel

Spain

Quantum transport

Electronic Transport Between Platinum Contacts Through Graphene/Nanotubes Structures

Sinitsyna

Olga

Russia

Spectrocopies and microscopies

New promising pyrolytic graphite for micromechanical exfoliation of graphene

Senior

Sivek

Jozef

Belgium

Other 2 dimensional materials

First-principles investigation of titanium and titanium dioxide adsorption on graphene

Student

Son

Jangyup

Spectrocopies and microscopies

In-situ Raman study on CVD-grown graphene microbridge under high current density

Student

Song

United Kingdom

Spitalsky

Zdeno

Slovakia

Strobl

Karlheinz

Sul

Onejae

Szpak

Interacting electrons and spin-splitting in graphene and graphene nanoribbons in the quantum Hall regime

Applications (gaz sensors, Fabrication and Applications of Graphene in composites, nanoelectronic Loughborough University devices...) Applications (gaz sensors, New Electric Conductive Polymeric composites, nanoelectronic Nanocomposites Based on Graphene devices...) Growth, synthesis 3D CVDGraphene™ Material Production Scale-up techniques and integration Process using Ni powders methods

Student

Senior

Korea

Spectrocopies and microscopies

Controlling the Chirality of Graphene’s edges using Polarization Selective Laser Annealing

Senior

Nikodem

Germany

Quantum transport

A sheet of graphene – quantum field in a discrete curved space

Senior

Themlin

Jean-Marc

France

Spectrocopies and microscopies

Reversible Formation and Hydrogenation of Deuterium-Intercalated Quasi-Free-Standing Graphene on 6H-SiC(0001)

Thiele

Cornelius

Germany

Toke

Csaba

Hungary

Trinsoutrot

Pierre

France

Troppenz

Gerald V.

Germany

Trusovas

Romualdas

Lithuania

Turchanin

Andrey

Germany

Ullrich

Daniela

Germany

Growth, synthesis Electron-beam-induced direct etching of techniques and integration Graphene methods Magnetism and Spintronics Excitations of bilayer graphene in the quantum Hall regime

Senior

Student

Senior

Growth, synthesis Experimental study of nucleation and growth Student techniques and integration mechanisms of graphene synthesized by Low methods Pressure Chemical Vapor Deposition on copper foil Spectrocopies and microscopies

Strain analysis of CVD graphene by in situ Raman spectroscopy

Growth, synthesis Graphite Oxide Reduction to Graphene Applying techniques and integration Ultrashort Laser Pulses methods Growth, synthesis A molecular route to 1 nm thick carbon techniques and integration nanomembranes (CNMs) and graphene for methods functional applications Spectrocopies and microscopies

Investigation of excitonic Fano resonances in graphene using optical spectroscopy

Student

Senior

Student

POSTERS

United States

Poster Title

211

Korea

Topic

Student Senior

Presenting Author

212

POSTERS

Presenting Author

Country

Topic

Van TUan

Dinh

Spain

Quantum transport

Vijay Gopal

Chilkuri

France

Chemistry of Graphene

Walters

Ian

Wang

Kangpeng

Wendelbo

Rune

Williams

United Kingdom China

Poster Title

Student Senior

Effect of Topological Disorder and Spin-Orbit Coupling in the Transport Properties of Graphene

Student

On the Interaction of Beryllium atoms with Graphene Nanostructures

Applications (gaz sensors, Plasma production and functionalisation of composites, nanoelectronic Graphene and GNPâ&#x20AC;&#x2122;s by plasma exfoliation devices...)

Student

Senior

Other 2 dimensional materials

Ultrafast Nonlinear Optical Responses of 2D MoS2 Student Nanosheets

Norway

Chemistry of Graphene

A Robust, Scalable Process for Automated Production of Highly Dispersed Graphene Oxide and its use in transparent conductive coatings

Senior

John

United Kingdom

Chemistry of Graphene

Development of Nano-Composites which include Plasma Functionalized Graphene Nanoplatelets

Student

Wilson

Neil

United Kingdom

Chemistry of Graphene

The real graphene oxide revealed: stripping the oxidative debris from the graphene-like sheets

Senior

Witowski

Andrzej

Poland

Wlasny

Igor

Poland

Wojtoniszak

Malgorzata

Poland

Zhong-Shuai

Germany

Xia

Zhenyuan

Italy

Chemistry of Graphene

Yaish

Yuval

Israel

Quantum transport

Yan

China

Chemistry of Graphene

Youn

Doo-Hyeb

Korea

Lili

Spectrocopies and microscopies

Characterisation of multilayer grapheene obtained by SiC sublimation on C surface by far infrared magnetospectroscopy and Raman spectroscopy Scanning Tunneling Spectroscopy (STS) studies of Graphene-Au interactions

Growth, synthesis Novel method of graphite exfoliation towards techniques and integration synthesis of graphene methods Applications (gaz sensors, Nitrogen Doped Graphene-Supported Fe3O4 composites, nanoelectronic Nanoparticles for Efficient Oxygen Reduction devices...) Reaction Nanoscale Comparison of graphite exfoliation by supramolecular, chemical and electrochemical methods Chemical Potential of Inhomogeneous Single Layer of Graphene Reaction Mechanisms of Chemical Reduction of Graphene Oxide by Sulfur-Containing Compounds ďź&#x161;A DFT Study

Applications (gaz sensors, High Power Light Emitting Diode Operation with composites, nanoelectronic Graphene Transparent Electrode devices...)

United States Other 2 dimensional materials

Current Saturation in Few-layer MoS2 FET

Senior

Student

Senior

Student

Topic

Poster Title

Zan

Recep

United Kingdom

Spectrocopies and microscopies

Interaction of Metals with suspended Graphene observed by Transmission Electron Microscopy

Zanolli

Zeila

Belgium

Quantum transport

Quantum spin transport in carbon chains with graphene-like contacts.

Zarenia

Mohammad

Belgium

Zebrev

Gennady

Zhang

Xiaoyan

Netherlands Chemistry of Graphene

Zhu

Shou-En

Netherlands Nanoelectromechanical systems

Ziatdinov

Maxim

Russia

Japan

Applications (gaz sensors, Energy levels of quantum rings in bilayer composites, nanoelectronic graphene devices...) Quantum transport

Spectrocopies and microscopies

Two-dimensional charge relaxation in graphene: generalized telegraph equations and pseudorelativistic invariance

Student Senior Student

Senior

Student

Senior

A novel way to prepare soluble graphene through Student organic functionalization on graphene Graphene nanomechanical piezoresistive sensor

Student

Visualization of electronic states along the boundaries of graphite nanoholes

Student

POSTERS

Country

213

Presenting Author

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