Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D25: Focus Session: Graphene III: Growth and Structure |
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Sponsoring Units: DMP Chair: Alessandra Lanzara, University of California, Berkeley Room: 327 |
Monday, March 16, 2009 2:30PM - 2:42PM |
D25.00001: Synthesis, characterization and thermal stability of CVD-grown graphene nanoribbons Jessica Campos-Delgado, Y.A. Kim, Endo Morinobu, Katsumi Kaneko, Humberto Terrones, Mildred S. Dresselhaus, Mauricio Terrones A route to produce large amounts of nanometer scale graphene ribbons is presented. The process involves the thermal decomposition of ethanol-ferrocene and minute concentrations of thiophene solutions. The material consists of stacked graphene sheets with dimensions of several microns in length, 100-500 nm in width and 10-20 nm in thickness. The morphology and structure of such material have been studied by SEM, HRTEM, Raman spectroscopy, XRD, XPS, TGA. In order to investigate the thermal stability of the pristine material, the as-prepared ribbons were annealed at various temperatures in the range 1000 $^{\circ}$C to 2800 $^{\circ}$C. The annealing treatments induced interesting structure changes in the samples, such as defect annihilation and loop formation at the edges, confirmed by HRTEM. A Raman spectroscopy study with many laser energies, enabled us to observe the overall behavior of the main Raman features (D, G, D', G', D+G bands). These phenomena will be discussed in detail. [Preview Abstract] |
Monday, March 16, 2009 2:42PM - 2:54PM |
D25.00002: Nitrogen-induced structures in epitaxial graphene on 6H-SiC(0001) Guofeng Sun, Sung-hyon Rhim, Yun Qi, Michael Weinert, Lian Li Nitrogen-induced structures on epitaxial graphene grown on 6H- SiC(0001) are studied by scanning tunneling microscopy (STM) and first-principles calculations. Several defect structures produced by nitrogen incorporation are observed by STM. Calculations of the energetics of nitrogen substitution at various sites neighboring a carbon vacancy indicate that nitrogen prefers to be at the site nearest to the vacancy, consistent with the STM observations. [Preview Abstract] |
Monday, March 16, 2009 2:54PM - 3:30PM |
D25.00003: Large area, Few Layer Graphene Films on Insulating Substrates Invited Speaker: Graphene has exceptional electronic, thermal and mechanical properties. For the realization of graphene-related applications, it is necessary to develop reliable and low cost fabrication methods of graphene-based structures, ideally on any substrates. In this talk I will present our method of fabricating large area ($\sim $cm$^{2})$ films of single- to few-layer graphene and transferring the films to arbitrary substrates. The graphene films are synthesized by ambient pressure Chemical Vapor Deposition, consist of regions of 1 to $\sim $10 graphene layers and have an average thickness of 2-3 nm. Despite their ultra-thin nature, the films thus produced are continuous over the entire area. Regions of single- or bi-layer graphene with lateral sizes of up to 25 $\mu $m were observed. High Resolution Transmission Electron Microscopy (HRTEM) and electron diffraction revealed that they are crystalline over the entire area and their Raman features were compared to those of graphene derived from mechanical exfoliation of Highly Oriented Pyrolytic Graphite (HOPG). Transistor devices made from these graphene show similar characteristics to ones made from graphitized SiC. Scanning tunneling microscopy imaging reveals interesting Mori\'{e} patterns and helpful insights for the growth of the graphene films on the Ni substrate. The method presented in this work can potentially be scaled to industrial production of graphene films, for applications such as ultra-thin conductive and transparent electrodes, or devices and interconnect for integrated circuits. [Preview Abstract] |
Monday, March 16, 2009 3:30PM - 3:42PM |
D25.00004: Kelvin Probe Microscopy of Single- and Multi-layer Graphene on SiO$_{2}$. Alexandra Curtin, Theresa Swanson, Michael S. Fuhrer Kelvin probe microscopy (KPM) was carried out on mechanically exfoliated graphene samples on SiO$_{2}$ in conjunction with standard atomic force microscopy. Potential differences between the SiO$_{2}$ substrate and graphene flakes were large relative to the average fluctuations over the surface of the graphene. KPM shows a consistent surface potential variation between monolayer, bilayer, and multi-layer graphene, and over folded pleats occasionally found in graphene. The source of these surface potential differences will be discussed. [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 3:54PM |
D25.00005: Evidence of the role of contacts on the observed electron-hole asymmetry in graphene Nimrod Stander, Benjamin Huard, Joseph Sulpizio, David Goldhaber-Gordon Most experiments on graphene devices show a clear difference between the conductances at exactly opposite densities, a phenomenon that has been attributed to different scattering cross sections off charged impurities for opposite carrier polarities. In this talk, we show that properties of the interface between graphene and metal contacts can also lead to such an asymmetry even when bulk graphene transport is particle-hole symmetric. By performing electrical transport measurements in graphene with several sample geometries, with both ``invasive'' probes and ``external'' probes, and with different metal contacts, we associate the asymmetry to \emph{p-n} or \emph{p-p} junctions forming at the interface graphene-metal. [Preview Abstract] |
Monday, March 16, 2009 3:54PM - 4:06PM |
D25.00006: Observation of graphene bubbles and effective mass transport under graphene films Daniil Stolyarov, Elena Stolyarova, Kirill Bolotin, Li Liu, Sunmin Ryu, Kwang Rim, Mark Hybertsen, Igor Pavlishin, Martin Klima, Igor Pogorelsky, Karl Kusche, James Hone, Philip Kim, Horst Stormer, Vitaly Yakimenko, George Flynn Mechanically exfoliated graphene mounted on a SiO$_{2}$/Si substrate was subjected to HF/H$_{2}$O etching or irradiation by energetic protons. In both cases gas was released from the SiO$_{2}$ and accumulated at the graphene/SiO$_{2}$ interface resulting in the formation of ``bubbles'' in the graphene sheet. Formation of these ``bubbles'' demonstrates the robust nature of single layer graphene membranes, which are capable of containing mesoscopic volumes of gas. In addition, effective mass transport at the graphene/SiO$_{2}$ interface has been observed. [Preview Abstract] |
Monday, March 16, 2009 4:06PM - 4:18PM |
D25.00007: Planar tunneling spectroscopy of graphite Richard Jones, Wan Kyu Park, Sam Johnson, Xin Lu, Nadya Mason, Laura Greene The electronic properties of graphite/graphene have become an intriguing area of research in recent years. Probing their electronic density of states (DOS) is of fundamental importance. For this purpose, we choose to do tunneling spectroscopy based on planar junctions. We prepare planar tunnel junctions on graphite using superconducting and normal metal counter-electrodes. An AlO$_{x}$ tunnel barrier is deposited onto a cleaved surface of HOPG using atomic layer deposition, reactive sputtering, thermal oxidation, or plasma oxidation. Differential conductance spectra are taken as a function of temperature down to 4.2K. In general, conductance increases with bias-voltage, which is qualitatively consistent with the predicted DOS in graphite. However, variances in the detailed structures are observed, including a zero-bias conductance dip and multiple peak and hump structures. We will also discuss different growth techniques we propose to yield reproducible junction characteristics. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D25.00008: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 4:30PM - 4:42PM |
D25.00009: Elasticity and Electron Fractionalization in Graphene William Shively, Dmitri Khveshchenko Much of the recent excitement over graphene comes from the fact that, at half-filling, the energy spectrum may be effectively described by a pair of Dirac fermions, giving rise to a host of effective (2+1)-d chiral gauge theoretic phenomena. In the presence of lattice distortions, hopping electrons bind to topological defects in the honeycomb lattice structure, which can lead to electron fractionalization. Recent work [c.f. Hou et al, PRL \textbf{98} (2007); Jackiw \& Pi, PRL \textbf{98} (2007)] has shown that for Peierls distortions - which in the case of graphene would be described by a Kekul\'{e} lattice dimerization pattern - such fractionalization may occur when electrons interact with topologically-induced vortices. Approaching the problem differently, here we develop a general theory of elasticity for honeycomb lattice structures with various non-trivial dimerization patterns, and explore concomitant possibilities of electron fractionalization. [Preview Abstract] |
Monday, March 16, 2009 4:42PM - 4:54PM |
D25.00010: Electrical Transport in Graphene Hybrid Structures Feng Miao, Wenzhong Bao, Hang Zhang, Chun Ning Lau Graphene, monolayer carbon atoms with honey-comb lattice, has intrigued condensed matter physics field for its unique electrical properties since its first discovery in 2004. The graphene hybrid structures that consist of both single and bi-layers were also experimentally studied recently for its novel properties. We will present our experimental study on the electron transport in graphene hybrid structures and the latest experimental data will be discussed in terms of various theoretic models. [Preview Abstract] |
Monday, March 16, 2009 4:54PM - 5:06PM |
D25.00011: Dependence of the Low Energy Electronic Structure of Multi-layer Graphene on Stacking Order Probed by Infrared Absorption Matthew Sfeir, Kin Fai Mak, James Misewich, Tony Heinz Optical conductivity spectra of multi-layer graphene samples were determined for photon energies in the range of 0.2 -- 1.0 eV. The measurements were performed using synchrotron radiatiaon on well-characterized exfoliated graphene samples on a transparent substrate. We observed distinct optical conductivity spectra for different samples having precisely the same number of layers. In particular, two well-defined types of spectra were obtained in measurements of more than a dozen of four-layer samples. This result can be understood by considering the existence of two stable configurations of four-layer graphene, namely, the ABAB Bernel stacking and the ABCA rhombohedral stacking. The observed absorption features were reproduced by explicit calculations, within a tight-binding model, of the optical conductivities for the two stacking sequences. We have thus shown the possibility of identifying these different crystallographic structures optically. Further, the significant difference found in the low-energy electronic structure suggests that the charge transport behavior of multilayer graphene may also depend on stacking order. [Preview Abstract] |
Monday, March 16, 2009 5:06PM - 5:18PM |
D25.00012: AFM study of the ridge-like network on epitaxial few-layer graphene grown on 4H-SiC [0001] Gyan Prakash, Michael Capano, Michael Bolen, Dmitry Zemlyanov, Ronald Reifenberger Few-layer graphene (FLG) is produced when SiC is heated to temperatures T$>$1475$^{\circ}$C under vacuum conditions. The FLG found on SiC exhibits a 2D mesh of interconnected ridges that extends over many square microns. Smooth regions of FLG are surrounded by the 2D ridges, forming a tile-like surface morphology. The origin of the network is attributed to the compressive stress generated by cooling. For FLG growth at moderately higher temperatures, the thickness of the FLG increases. Under these conditions, AFM studies reveal the emergence of a few well-defined folds that relax the surface stress. In contrast to the previous ridge-like network, the folds appear at only a few locations and have a greater height than the ridges. This AFM study provides insights on how to improve the quality of FLG material grown at elevated temperatures on SiC substrates. [Preview Abstract] |
Monday, March 16, 2009 5:18PM - 5:30PM |
D25.00013: Moir\'{e} Patterns: Fingerprints of Few-Layer Epitaxial Graphene Growth on 4H-SiC(000$\bar{1}$) Laura Biedermann, Michael Bolen, Michael Capano, Dmitry Zemlyanov, Ronald Reifenberger Few-layer epitaxial graphene (FLG) was grown by heating [000$\bar{1}$] silicon carbide to high temperatures (1350--1600$^{\circ}$C) in vacuum. A continuous graphene surface layer was formed at temperatures of 1475$^{\circ}$C and greater. X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used to characterize the quality, thickness, and topography of the FLG. STM studies revealed a wide variety of different nanometer-scale features that include rough graphene, 1D superlattices, grain boundaries, and Moir\'{e} 2D superlattices. Detailed studies of the Moir\'{e} superlattices showed enhanced conductivity due to density of states effects. These Moir\'{e} superlattices also provided insights into the growth mechanisms of FLG on the carbon-face of SiC. \\[0pt] L. Biedermann \textit{et al.}, ``Insights into Few-Layer Epitaxial Graphene Growth on 4H-SiC(000$\bar{1}$) Substrates from STM Studies,'' \textbf{Phys. Rev. B} (submitted). [Preview Abstract] |
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