Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U28: Focus Session: Graphene IV |
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Sponsoring Units: DMP Chair: Barbaros Qezyilmaz, Columbia University Room: Colorado Convention Center 302 |
Thursday, March 8, 2007 8:00AM - 8:12AM |
U28.00001: The advent, and physical properties, of new classes of graphene-based materials Rodney S. Ruoff, Inhwa Jung, Supinda Watcharotone, Geoffrey H. B. Dommett, Eric Zimney, Sasha Stankovich, Richard Piner, Sungjin Park, Dmitriy A. Dikin We have developed new materials based on chemically modified graphene (CMG) sheets. By working with aqueous colloidal suspensions of `graphene oxide' sheets (graphene sheets that are surface functionalized with hydroxyl, epoxide, carboxylate, and possibly other oxygen-containing functionalities), and at times by doing further chemistry to create a portfolio of CMG sheets, it has been possible to study (i) individual CMG sheets deposited on substrates designed for optical characterization of them (ii) electrical properties of individual CMG sheets (iii) fabrication {\&} properties of ceramic composites with embedded CMG sheets (iv) fabrication of novel ``paper-like'' materials (analogy: bucky paper) comprised of aligned CMG sheets and having thicknesses from less than 1 up to 20 micrometers. Here, we provide a broad overview of this work, and also new directions of research. Support from NASA ({\#} NCC-1-02037) through theURETI on Bio-inspired Materials, the Naval Research Laboratory ({\#}N00173-04-2-C003) and the NSF (CMS-0510212), is appreciated. [Preview Abstract] |
Thursday, March 8, 2007 8:12AM - 8:24AM |
U28.00002: The Structure of Suspended Graphene Jannik Meyer, Andre Geim, Mikhail Katsnelson, Kostya Novoselov, Tim Booth, Siegmar Roth The recent discovery of graphene has sparked significant interest, which has so far been focused on the peculiar electronic structure of this material, in which charge carriers mimic massless relativistic particles. However, the structure of graphene is also puzzling. On one hand, graphene appears to be a strictly 2D material and exhibits such a high crystal quality that electrons can travel submicron distances without scattering. On the other hand, perfect 2D crystals cannot exist in the free state, according to both theory and experiment. This is often reconciled by the fact that all graphene structures studied so far were an integral part of larger 3D structures, either supported by a bulk substrate or embedded in a 3D matrix. We describe individual graphene sheets freely suspended on a microfabricated scaffold. These membranes are only one atom thick and still display a long-range crystalline order. However, our studies by transmission electron microscopy have revealed that suspended graphene sheets are not perfectly flat but exhibit intrinsic microscopic roughening such that the surface normal varies by several degrees and out-of-plane deformations reach 1 nm. The atomically-thin single-crystal membranes offer an ample scope for fundamental research and new technologies whereas the observed corrugations in the third dimension may shed light on subtle reasons behind the stability of 2D crystals. [Preview Abstract] |
Thursday, March 8, 2007 8:24AM - 8:36AM |
U28.00003: Electrostatic Deposition of Graphene Anton Sidorov, Gamini Sumanasekera, Mehdi Yazdanpanah, Romaneh Jalilian, P. Ouseph, Robert Cohn Loose graphene sheets, one to a few atomic layers thick are often observed on freshly cleaved HOPG surfaces. A simple and reliable technique using electrostatic attraction is demonstrated to transfer these graphene sheets to a selected substrate. Sheets from one to 22 layers thick have been transferred by this method. One sheet after initial deposition is measured by atomic force microscopy to be only atomic layer thick ($\sim $ 0.35 nm). A few weeks later, this height is seen to increase to $\sim $ 0.8 nm. Raman spectroscopy of a single layer sheet shows the emergence of an intense D band which dramatically decreases as the number of layers in the sheet increase. The intense D band in monolayer graphene is attributed to the graphene conforming to the roughness of the substrate. [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U28.00004: Characterization and Patterning of Ultrathin Epitaxial Graphene Grown on 4H-SiC Xuebin Li, Zhimin Song, Michael Sprinkle, Xiaosong Wu, Claire Berger, Walter de Heer Ultrathin graphite films are grown on the C face (000-1) of insulating single crystal 4H-SiC substrates by high temperature thermal decomposition of SiC. The films are characterized extensively. Atomic force microscopy images show extended atomically flat micron size terraces. Magneto-transport measurements indicate that transport of the films is dominated by the interface graphene layer which is electron-doped due to the built-in electric field at the interface. The films can be patterned with conventional lithography techniques and ribbons with widths less than 10nm can be produced. We present experimental results on several patterned gated structures. [Preview Abstract] |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U28.00005: ABSTRACT HAS BEEN MOVED TO P27.00015 |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U28.00006: Structural and mechanical properties of `graphene oxide'-based paper Dmitriy A. Dikin, Eric J. Zimney, Sasha Stankovich, Richard D. Piner, Geoffrey H. B. Dommett, Rodney S. Ruoff Free standing membranes (GO paper) were produced by exfoliation of graphite oxide in water to individual `graphene oxide' sheets (as a colloidal suspension) followed by their re-assembly by vacuum filtration. Study of the structure and morphology of the GO paper revealed that it is composed of highly packed and ordered layers of graphene oxide sheets separated by water molecules. Measurements of the mechanical response under tensile load revealed elastic deformation for small strain, followed by plastic deformation again for a relatively small region of strain, and then fracture without pullout of individual sheets or multi-layer stacks. GO paper possesses high modulus values of about 40 GPa and strength values around 130 MPa; each much higher than modulus or strength values for Bucky-paper or Grafoil. The experimental results support the conclusions of very effective load distribution and good binding between the GO sheets in which the self-adjusted amount of interlayer water plays a central role. After the deoxygenation of GO sheets the fabricated paper becomes a tunable semiconductor. Support from NASA (Award {\#} NCC-1-02037) through the University Research, Engineering, and Technology Institute on Bio-inspired Materials is appreciated. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:24AM |
U28.00007: Generation of Carbon Scrolls from Graphene films Humberto Gutierrez, Awnish Gupta, Qiujie Lu, Vincent Crespi, Peter Eklund Using a chemical process to delaminate graphene from HOPG, we are able to produce suspended graphene and n-graphene layer films (i.e., $n$GL\textbf{, }n=integer) in various organic solvents. The $n$GLs have lateral dimensions of several microns. We observe that in a matter of a few hours, the $n$GLs ``roll up'' on themselves to form scrolls. Here we present results of a study which investigates the role of the solvent in determining the characteristic time to ``roll up'' the $n$GL. Raman scattering, AFM and TEM is used to characterize the scrolls. A model will be presented to explain why the scrolling occurs. [Preview Abstract] |
Thursday, March 8, 2007 9:24AM - 9:36AM |
U28.00008: Mechanism of growth of a graphitic edge in a Carbon Monoxide atmosphere Sujata Paul, Erik E. Santiso, Marco B. Nardelli The interaction of CO with zigzag and armchair graphite edge has been studied using density functional theory. Our results suggest that the growth of a zig-zag graphene edge in a CO atmosphere may happen through a multiple steps. A possible growth mechanism will start through the formation of pentagon with the adsorption of CO on the edge. The cleaning of oxygen atoms from the edge could happen through the desorption of O$_{2}$ or desorption of CO$_{2. }$ Further chemisorption of CO will cover the edge with the formation of 5-7-5 structures. Such adsorptions of CO will be followed by desorption of O$_{2}$ or desorption of CO$_{2 }$ and finally through the rearrangement of the 5-7-5 structures, the zig-zag edge would be restored. On the contrary the growth of armchair graphite edge have only two steps. The formation of hexagonal structures upon adsorption of CO and desorption of top oxygen atoms as CO$_{2}$ or O$_{2}$ . Our results of energy calculations suggest that the growth in the direction of a armchair wall is more favorable. [Preview Abstract] |
Thursday, March 8, 2007 9:36AM - 9:48AM |
U28.00009: Boron doped graphene nanoribbons Thiago Martins, Hiroki Miwa, Antonio J.R. da Silva, A. Fazzio We will present a detailed study of the electronic, magnetic and transport properties of boron doped graphene nanoribbons, for various widths. The electronic structures and the equilibrium geometries were obtained through ab initio total energy DFT calculations. The transport properties were investigated using nonequilibrium Green's functions. Our results reveal that the substitutional boron atoms occupy the edge sites of nanoribbons, quenching the local ferromagnetism along the nanorribon edges. In addition, the presence of edge boron atoms break the symmetry between spin up and spin down transmittance channels. Those results suggest that, through a suitable doping process, it is possible to tailor the electronic current along the graphene nanoribbon. We thank FAPESP, CNPq and CENAPAD-SP. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:00AM |
U28.00010: Thermal-closing of holes put in single-graphene sheets of carbon nanotubes depending on its curvatures. Masako Yudasaka, Jin Miyawaki, Ryota Yuge, Takasumi Kawai, Jing Fan, Sumio Iijima Holes put in the walls of single-wall carbon nanotubes by oxidation are believed to be closed by heat treatment. We investigated this in detail using single-wall carbon nanohorn (SWNH), a type of single-wall carbon nanotubes. SWNHs are suitable to study this because they have high purities (95{\%}, no metal) and closed structure in the as-grown state, and the holes are easily opened by oxidation. Even numbers and sizes of holes are controllable. The nitrogen adsorption quantities measured at 77K clarified that the holes opened at the tips of tubes were closed easily by the heat treatment at 1473K in Ar, but those in the sidewalls were not, suggesting that the closing easiness depended on the tube curvatures. This was confirmed by the computer simulation. The hole closing kinetics of the tip holes was further investigated by changing the heat-treatment duration, as a result, two types of holes were found: one closed in a couple of minutes and the other in 30 minutes by the heat-treatment a 1473K, which may correspond to the variation of hole-sizes at the tips. [Preview Abstract] |
Thursday, March 8, 2007 10:00AM - 10:12AM |
U28.00011: Fabrication of graphene nanogaps by electrical breakdown Brian Standley, Emma Schmidgall, Marc Bockrath We have fabricated {\it n}-graphene nanogaps which may be useful as an alternative to the metallic contacts used in current single molecule transistors. The nanogaps are formed by electrical breakdown of two-terminal {\it n}-graphene devices. We have characterized the gaps by atomic force microscopy and electrical transport measurements, both of which suggest that the gaps are narrow enough to capture a single molecule. The {\it n}-graphene contacts' two dimensional nature is expected to improve gate control by reducing charge screening. Additionally, the contacts' atomic flatness may allow in situ scanning tunneling microscopy imaging of the transistor molecule. [Preview Abstract] |
Thursday, March 8, 2007 10:12AM - 10:24AM |
U28.00012: Structural Differences Between Graphite Grown on Si- and C- Terminated Polar Faces of 4H-SiC Joanna Hass, Rui Feng, Xuebin Li, Michael Sprinkle, Claire Berger, Edward Conrad In the last two years the transport properties of 2D graphene grown on SiC have shown that electron coherence lengths can exceed many microns. It is now critical to understand the source of these unique transport properties and explain their dependence on which polar face they are grown. We will present surface X-ray diffraction data that highlights the structural differences between graphite grown on C-terminated and Si-terminated 4H-SiC. We will show that the C-terminated graphite grows in domains more than an order of magnitude larger than the Si-terminated graphite.[1] Strain, islanding and complex rotational phases in the graphene will be presented. More importantly, X-ray reflectivity measurements reveal a tightly bound initial graphene layer, with a second graphene layer at an interlayer spacing significantly larger than in the bulk. The implications of this ``buffer'' layer will be discussed in terms of recent band structure calculations[2] and a possible explanation for transport seemingly being confined to a single graphene layer. [1] J. Hass, et al., App. Phys. Lett. \textbf{89}, 143106 (2006). [2] F. Varchon, et al., (to be published). [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 10:36AM |
U28.00013: Graphane: a two-dimensional hydrocarbon Jorge Sofo, Ajay Chaudhari, Greg Barber We predict the stability of a new\textit{ extended two-dimensional hydrocarbon} on the basis of first-principles total energy calculations. The compound that we call graphane is a fully saturated hydrocarbon derived from a single graphene sheet with formula CH. All of the carbon atoms are in sp$^{3}$ hybridization forming a hexagonal network and the hydrogen atoms are bonded to carbon on both sides of the plane in an alternating manner. Graphane is predicted to be stable with a binding energy comparable to other hydrocarbons such as benzene, cyclohexane, and polyethylene. We discuss possible routes for synthesizing graphane and potential applications as a hydrogen storage material and in two dimensional electronics. [Preview Abstract] |
Thursday, March 8, 2007 10:36AM - 10:48AM |
U28.00014: Morphology and crack toughness behaviour of PP-MWNT nanocomposites R. Weidisch, M. Ganss, B. K. Satapathy, P. Poetschke, D. Jehnichen, A. Janke Morphology and crack toughness of PP-MWNT nanocomposites have been studied by AFM-WAXD and essential work of fracture approach respectively. A ductile-to-semiductile transition in the crack resistance behaviour of PP-MWNT nanocomposites and its interrelation to the structural attributes studied by SEM and DSC has been discussed. A maximum in the non-essential work of fracture was observed at 0.5 wt.-{\%} MWNT demonstrating enhanced toughness compared to pure PP, followed by a sharp decline as the MWNT content was increased to 1.5 wt.-{\%} reveals a ductile-to-semiductile transition. Fracture kinetics studies presents a qualitative picture of the nature of such a transition in terms of (a) switch over from non-steady (in pure PP) to steady state crack-tip-opening-displacement rate (in nanocomposites) and (b) ductile-to-semiductile transition being largely due to delayed-yielding in the nanocomposites . The time-resolved analysis of strain field offering insight into the crack propagation kinetics has revealed that such a transition is caused by rapid development of critical local stresses causing a shift of crack initiation to shorter time, resulting in a semi-ductile fracture of nanocomposites containing 1.5 wt.{\%} MWNT. [Preview Abstract] |
Thursday, March 8, 2007 10:48AM - 11:00AM |
U28.00015: Electron fractionalization in two-dimensional graphene-like structures Chang-Yu Hou, Claudio Chamon, Christopher Mudry Electron fractionalization is intimately related to topology. In one-dimensional systems, fractionally charged states exist at domain walls between degenerate vaccua. In two-dimensional systems, fractionalization exists in quantum Hall fluids, where time-reversal symmetry is broken by a large external magnetic field. Recently, there has been a tremendous effort in the search for examples of fractionalization in two-dimensional systems with time-reversal symmetry. In this paper, we show that fractionally charged topological excitations exist on graphene-like structures, where quasiparticles are described by two flavors of Dirac fermions and time-reversal symmetry is respected. The topological zero-modes are mathematically similar to fractional vortices in $p$-wave superconductors. They correspond to a twist in the phase in the mass of the Dirac fermions, akin to cosmic strings in particle physics. [Preview Abstract] |
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