Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D22: Materials Chemically Derived from Graphene |
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Sponsoring Units: DMP DCMP Chair: Adalberto Fazzio, University of Sao Paulo, Brazil Room: Portland Ballroom 252 |
Monday, March 15, 2010 2:30PM - 2:42PM |
D22.00001: Structural study of graphene oxide (GO) and reduced and annealed graphene oxide (raGO) using aberration-corrected TEM Will Gannett, Kris Erickson, Rolf Erni, Zonghoon Lee, Nasim Alem, Alex Zettl Owing to its solubility compared to graphene, graphene oxide (GO) has become popular in recent years as a potentially scalable precursor to graphene in devices. After the GO's oxidation and defects are chemically and thermally removed, reduced and annealed graphene oxide (raGO) remains. Using aberration-corrected transmission electron microscopy, we examine both GO and raGO with single-atom resolution. The GO appears heavily oxidized and disordered, but interestingly many isolated graphitic regions persist. Observation of the raGO shows that while reduction is nearly complete, the process causes significant damage to the sheet, making it structurally unstable and electronically disordered. [Preview Abstract] |
Monday, March 15, 2010 2:42PM - 2:54PM |
D22.00002: High yield assembly and electron transport properties of reduced graphene oxide field effect transistors Daeha Joung, Anindarupa Chunder, Lei Zhai, Saiful I. Khondaker We demonstrate high yield fabrication of field effect transistors (FET) using chemically reduced graphene oxide (RGO) sheets which is compatible with complimentary metals oxide semiconductor technology. The RGO sheets suspended in water were assembled between prefabricated gold source and drain electrodes using ac dielectrophoresis (DEP). All of the devices showed FET behavior with the application of a gate bias with the majority of them demonstrating ambipolar behavior with a maximum hole and electron mobilities of 4.0 and 1.5 cm$^{2}$/Vs respectively. Current-voltage characteristic of the FET devices measured at different temperature follow power law behavior with $I\infty V^n$ with n=1 at low bias while n is as high as 3 at high bias voltage. The temperature dependence of the resistance show Efros-Shklovskii variable range hopping behavior proving that RGO devices are similar to that of disordered granular system. High yield assembly of RGO FET will have significant impact in scaled up fabrication of graphene based nanoelectronic devices. [Preview Abstract] |
Monday, March 15, 2010 2:54PM - 3:06PM |
D22.00003: Atomic and Electronic Structure of Graphene Oxide Sumit Saxena, Trevor A. Tyson, Shobha Shukla, Ezana Negusse, Haiyan Chen, Jaimin Bai, P. N. Prasad We have investigated the atomic structure of graphene oxide by DFT calculations. Our spin restricted ab-initio density functional calculations have shown that the oxygen link to the graphene basal plane using epoxide bonds. The flat graphene sheets are found to deform by buckling due to formation of C -- O -- C linkages normal to the plane of the graphene sheets. The calculations were compared with x-ray diffraction and x-ray spectroscopic measurements. Tentative models of the structure are proposed based on the combined DFT and experimental data. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:18PM |
D22.00004: In-situ Resistive Measurements of Graphite Oxide Reduction for Spin-Transport Based Devices Ira Jewell, Chien-Chih Huang, Sean Smith, Ashley Mason, Albrecht Jander, John Conley In this work, the thermal reduction to graphene of single and few-layer graphite oxide (GO) was characterized as a function of time using in-situ, four-point resistivity measurements. GO was produced chemically using a modified Hummer's method and then spray deposited onto an oxidized Si wafer. 100 nm Au with a 5 nm Cr adhesion layer was thermally evaporated onto the randomly dispersed GO, and then defined lithographically into an array of four point probe contact structures. High-temperature probes were used to make contact with the samples in a furnace tube where the GO was heated to 300 \r{ }C for 30 minutes under forming gas atmosphere (90{\%} N$_{2}$/10{\%} H$_{2})$. The measured conductance increased several orders of magnitude as the insulating properties of GO transitioned to the semi-metallic properties of graphene. Graphene and GO were further characterized before and after thermal reduction using atomic force microscopy (AFM) and Raman spectroscopy. We also report on similar experiments using ferromagnetic CoFe contacts for spin-dependent transport experiments. [Preview Abstract] |
Monday, March 15, 2010 3:18PM - 3:30PM |
D22.00005: Electronic structure and localization behavior of hydrogenated graphene Junhyeok Bang, K. J. Chang Graphene, i.e., a single layer of graphite, has attracted much attention because of its unique electronic properties such as zero gap and massless Dirac fermions. More interestingly, this system remains metallic even in the presence of long range disorders. Delocalization of carriers is attributed to the absence of back scattering. Recently, it was reported that graphene undergoes a metal-to-insulator transition by hydrogenation. However, its origin is not clearly understood yet. Here we study the electronic and transport properties of hydrogenated graphene through first-principles and tight-binding calculations. When H atoms bond randomly to only the C atoms in the A sublattice, the band gap is developed, with nearly degenerate impurity levels lying at the Dirac point. If H atoms are randomly adsorbed at both the A and B sublattice sites, the impurity band with a finite width is formed near the Dirac point due to interactions between the impurity levels. In the latter case, we find that conductance decays exponentially with increasing of the sample size, following the single parameter scaling theory of Anderson localization. [Preview Abstract] |
Monday, March 15, 2010 3:30PM - 3:42PM |
D22.00006: First-Principles Study of Graphene Channel on Graphite Monofluoride Ning Shen, Jorge Sofo We propose the formation of graphene regions in a matrix of graphene monofluoride as a method to confine the charge carriers in graphene. Graphene is an excellent conductor and graphene monofluoride is a wide band gap semiconductor. Removing fluorine from graphene monofluoride creates regions of graphene where the charge carriers are confined by the band gap of the fluorinated parts. In particular, we study the electronic structure of graphene stripes drawn on monofluoride. On the basis of first-principles calculations, we show that the monofluoride regions preserve its property as good insulator while the graphene channel exhibits interesting electronic and magnetic properties. We study two high symmetry orientations, armchair and zig-zag. The armchair orientation is found to have a non-magnetic ground state with a band gap dependent on the width of the graphene channel. The zigzag orientation is found to have anti-ferromagnetic ground state while the ferromagnetic state is about 1meV higher in energy for wide channel. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 3:54PM |
D22.00007: Opening a bandgap in graphene by fluorination Bei Wang, B.J. Cooley, S.-H. Cheng, K. Zou, Q.Z. Hao, F. Okino, J. Sofo, N. Samarth, J. Zhu The zero bandgap of graphene underpins many of its unique electronic properties. A band gap is desirable, however, for many electronic and optical applications. Chemical modifications of the graphene sheet can drastically change its conductivity. Following this strategy, both oxygenation and hydrogenation of graphene have been demonstrated. In this study, we present a reversible method of modifying the band structure of graphene through fluorination. Reacting graphite with fluorine gas at high temperature results in nearly 100{\%} fluorinated graphite fluoride, where each carbon atom is covalently bonded to a fluorine atom. Remarkably, the layered structure and hexagonal in-plane crystalline order are preserved in graphite fluoride. We obtain few-layer graphene fluoride through stamping method and report the optical and transport properties of this extremely insulating 2D compound, which is expected to be a wide band gap semiconductor. ~ [Preview Abstract] |
Monday, March 15, 2010 3:54PM - 4:06PM |
D22.00008: Hierarchy of Electronic Properties of Chemically Derived and Pristine Graphene Probed by Microwave Imaging Worasom Kundhikanjana, Keji Lai, Hailiang Wang, Hongjie Dai, Michael Kelly, Zhi-Xun Shen AFM-compatible near-field microwave impedance microscope (MIM), capable of measuring local complex dielectric constant with 100 nm resolution, is used to study graphene in different modalities, with a hierarchy of electrical properties. The low-conductivity graphite oxide and its derivatives show significant electronic inhomogeneity. In the low DC resistance chemically exfoliated graphene sheets, the residual defects lead to appreciable electronics inhomogeneity. In contrast, the signals from pristine graphene are homogenous over the whole pieces. MIM provides an effective way to conduct a statistical study on many graphene pieces without requiring any contact electrode. When plotted as a function of the sheet areas, the signals from the pristine graphene agree well with a lumped-element circuit model, as expected for good conductors, while the signals from the chemical graphene systematically fall below the expected curve. The local impedance can also be used to verify the electrical contact between overlapped graphene pieces -- critical information but difficult to obtain by other methods. [Preview Abstract] |
Monday, March 15, 2010 4:06PM - 4:18PM |
D22.00009: Effects of hydrogen exposure on monolayer graphene on SiC(0001) Chariya Virojanadara, Alexei Zakharov, Rositza Yakimova, Leif Johansson The influence of hydrogen exposures on a high quality monolayer graphene grown on SiC(0001) is investigated using photoelectron spectroscopy (PES), low-energy electron microscopy (LEEM) and micro low energy electron diffraction ($\mu $-LEED). We observe significant changes in the C1s core level, electron reflectivity curve, and electron diffraction after hydrogenation. Collected LEEM and $\mu $-LEED data after atomic hydrogen exposures demonstrate unambiguously a transformation from monolayer graphene plus carbon buffer layer to bi-layer graphene with no carbon buffer layer. This is novel since the preparation of either homogenous large area bi-layer graphene or bi-layer graphene without the carbon buffer (interface) layer on SiC(0001) has earlier not been reported. Our findings therefore open up new possibilities and opportunities for graphene-SiC based electronic devices and hydrogen storage. [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:30PM |
D22.00010: Chemical functionalization of suspended graphene membrane - a combined first-principles and experimental study Wei Wang, Efthimios Kaxiras, Robert Westervelt A single-atomic layer membrane, graphene is a unique material with ultimate large surface area for a given volume. These surfaces are inert and stable enough to confront rather harsh chemical and/or physical environment and maintains its structural integrity, yet they are active and versatile enough to chemically interact with various absorbate and form new crystalline or disordered structures that trigger dramatic change of its properties such as conductor-isolator transition. In this study, we use first principle calculations to explore the interactions among graphene and a variety of ions and functional groups, showing how each of these species or the combination of these species interact with graphene and in turn change its structural, electric, magnetic and phonon properties. In addition, we discuss experimentally detecting and characterizing chemically functionalized graphene structure with Raman spectroscopy and aberration corrected transmission electron microscopy. [Preview Abstract] |
Monday, March 15, 2010 4:30PM - 4:42PM |
D22.00011: A Planar, Semiconducting Graphene Allotrope David Appelhans, Zhibin Lin, Mark Lusk A number of graphene allotropes have been proposed which maintain a two-dimensional carbon structure while exhibiting interesting mechanical and electronic properties. In recent works, we have shown how these new carbon phases, pentaheptite, the haeckelites, and the dimerites, can be constructed from graphene using a combination of Stone-Thrower-Wales (STW) and Inverse Stone-Thrower-Wales (ISTW) defects. Significantly, all of these allotropes are metallic, and this limits the manner in which they might be incorporated into the emerging field of carbon electronics. Motivated by this, we have employed di-vacancies (DVs) as the third member of a defect alphabet to broaden the design space for technologically important carbon sheets. This has resulted in the identification of a metallic, planar graphene allotrope with a lower ground state energy than any previously identified. Even more important, though, is the computational discovery of a relatively low-energy, planar, semi-conducting allotrope. This material can be fabricated entirely from SW and DV defects and can also be created as both islands and ribbons within an existing graphene sheet. This offers the prospect of creating electronic components solely using graphene defect engineering. We employ a combination of density functional theory (DFT) and screened Green function (GW) theory to elucidate the structure and electronic properties of this new semiconductor. [Preview Abstract] |
Monday, March 15, 2010 4:42PM - 4:54PM |
D22.00012: Hydrogen bond networks in Graphene Oxide Composites: Structure and Mechanical Properties Nikhil Medhekar, Vivek Shenoy A composite structure made of several layers of graphene oxide has drawn a considerable attention as a paper-like composite material due to its excellent electronic and mechanical properties. Using molecular dynamics simulations, we study the atomic-level structure of such multilayer graphene oxide composites. We find that in these structures, the individual graphene oxide layers are interlinked via a non-uniform network of hydrogen bonds mediated through oxygen-containing functional groups and water molecules. Based on a quantitative analysis of hydrogen bond networks, we show that they play a crucial role in determining the overall morphology of graphene oxide composites. The predicted structural and mechanical properties are in good agreement with experimental observations. [Preview Abstract] |
Monday, March 15, 2010 4:54PM - 5:06PM |
D22.00013: Patterning graphene at the nanometer scale via hydrogen desorption Paolo Sessi, Jeffrey Guest, Matthias Bode, Nathan Guisinger We have demonstrated the reversible and local modification of the electronic properties of graphene by hydrogen passivation and subsequent electron-stimulated hydrogen desorption with an STM tip. In addition to changing the morphology, we show that the hydrogen passivation is stable at room temperature and modifies the electronic properties of graphene, opening a gap in the LDOS. This insulating state is reversed by local desorption of the hydrogen, and the unaltered electronic properties of graphene are recovered. Using this mechanism, we have ``written'' graphene patterns on nanometer length scales. This reversible and local mechanism for modifying the electronic properties of graphene has far-reaching implications for nanoscale circuitry fabricated from this revolutionary material. [Preview Abstract] |
Monday, March 15, 2010 5:06PM - 5:18PM |
D22.00014: Traditional and Novel dielectric dielectric materials for Epitaxial Graphene electronics applications Yike Hu, Claire Berger, Walt de Heer Graphene field effect transistor performance relies on the quality of the dielectric and its interaction with the graphene layer. The high frequency cutoff is currently, for a large part related to losses and mobility reductions caused by the dielectric overlayers. We will present a progress report on traditional (ALD) dielectrics as well as novel approaches including chemically modified graphene. [Preview Abstract] |
Monday, March 15, 2010 5:18PM - 5:30PM |
D22.00015: High-Throughput, Ultrafast Synthesis of Solution Dispersed Graphene via a Facile Hydride Chemistry Nihar Mohanty, Ashvin Nagaraja, Jose Armesto, Vikas Berry Graphene's superior electrical, optical {\&} mechanical characteristics and its continuously growing applications require concomitant development of graphene-processing-technology. In this talk, we will demonstrate the ability of sodium hydride to act both as a reducing agent and as a deprotonator of methanol, to instantaneously (in few seconds) reduce methanol dispersed graphene-oxide (GO) to reduced graphene oxide (RGO) sheets while simultaneously deprotonating methanol to methoxy ions, which then stabilize the RGO sheets in the methanol with a yield of $\sim $ 68 {\%}. This novel chemistry is effective in producing RGO with a high ratio of sp$^{2}$ to sp$^{3}$ carbon densities, where the average sp$^{2}$ domain size increases from 4 nm$^{2}$ to 12.25 nm$^{2}$ after reduction. The bilayer RGO sheets produced from this method exhibit carrier mobilities of 100-600 cm$^{2}$V$^{-1}$S$^{-1}$. The high-throughput processing, high-stability of the RGO dispersion, and the benignity {\&} low-cost of the reagents involved will enable expedited research and incorporation of high-quality graphene into next-generation graphene technologies {\&} applications. [Preview Abstract] |
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