Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J37: Focus Session: Graphene Growth, Characterization, and Devices: Surface Studies |
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Sponsoring Units: DMP Chair: Phil First, Georgia Institute of Technology Room: C146 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J37.00001: Scanning Tunneling Microscopy of Graphene on a Boron Nitride Substrate Yang Wang, Regis Decker, Victor Brar, William Regan, Hsin-Zon Tsai, Qiong Wu, Alex Zettl, Michael Crommie Graphene placed on a boron nitride (BN) substrate has been shown to result in increased mobility and improved Quantum Hall measurements.\footnote{Dean, CR \textit{et al.} Boron nitride substrates for high-quality graphene electronics. \textit{Nature Nanotechnology} \textbf{5}, 722-726 (2010)} It is therefore of great interest to understand how BN substrates differently influence graphene compared to more standard SiO$_{2}$ substrates. I will present new scanning tunneling microscopy measurements of graphene placed on a BN substrate. Differences in the local behavior of graphene on a BN substrate versus a SiO$_{2}$ substrate will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J37.00002: STM study of graphene on boron nitride Jiamin Xue, Danny Bulmash, Javier Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, Pablo Jarillo-Herrero, B.J. LeRoy We have performed low-temperature STM topographic and spectroscopic measurements of graphene on h-BN. We found that the topographic variations are reduced as compared to graphene on SiO2. We also performed scanning tunneling spectroscopy measurements to study the spatial variation of the Dirac point. We will present our latest results on the topographic and spectroscopic features for graphene on h-BN and compare them with similar measurements for graphene on SiO2. [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J37.00003: Atomic-Scale Topographic and Electronic Structure of Graphene Films on Ultraflat Insulating Materials Christopher Gutierrez, Liuyan Zhao, Fereshte Ghahari, Cory Dean, Kwang Rim, James Hone, George Flynn, Philip Kim, Abhay Pasupathy Graphene, a unique two-dimensional material, has attracted much attention for its exotic electronic properties. But owing to its nature as a single monolayer, many of these interesting properties depend heavily on the substrate on which the graphene rests. Scanning tunneling microscope (STM) experiments offer the unique ability to investigate the effect of the substrate on the surface roughness (via topography maps) as well as the local electronic properties (via spectroscopy maps) of graphene. In this talk we will present such experimental results of graphene on atomically flat insulating substrates such as mica and boron nitride, as well as suspended graphene sheets. We will describe experiments performed both on exfoliated graphene flakes as well as large-area graphene films grown by chemical vapor deposition (CVD). [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:27PM |
J37.00004: Structural and electronic properties of epitaxial graphene on SiC(0001): Growth, transfer doping and atomic intercalation Invited Speaker: Epitaxial graphene on SiC(0001) promises a scalable graphene technology. Growth methods and experimental techniques for layer counting will be reviewed. The graphene layers are n-doped due to the influence of a covalently bonded carbon interface layer. This doping level can be precisely tailored and completely neutralized by functionalizing the graphene surfaces with electronegative molecules. In particular the Fermi level can be shifted into the band gap of bilayer graphene. The influence of the interface can be completely eliminated by hydrogen intercalation. Hydrogen migrates under the interface layer, passivates the underlying SiC layer and decouples the graphene from the substrate. The interface layer alone transforms into a quasi-free standing monolayer and epitaxial monolayer graphene turns into a decoupled bilayer. By intercalation of Germanium the graphene layers can also be decoupled. In this process both p- and n-doping can be obtained, depending on the amount of Ge intercalated. Both phases can be prepared simultaneously on the surface, so that lateral p-n junctions can be envisioned. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J37.00005: Scanning Tunneling Spectroscopy of Suspended Graphene in the Quantum Hall Regime Nikolai N. Klimov, Suyong Jung, Gregory M. Rutter, Nikolai B. Zhitenev, David B. Newell, Joseph A. Stroscio The discovery of graphene, a unique two-dimensional electron system with extraordinary physical properties, has ignited tremendous research activity in both science and technology. Graphene interactions with a substrate such as, for example, SiO$_{2}$/Si are known to strongly limit the electrical performance of graphene devices. Suspended graphene devices, where interaction with substrates can be strongly reduced, have been studied by macroscopic transport measurements and shown to have a 10-fold increase in mobility. However, a detailed investigation on a microscopic scale is still missing. In this talk we present a scanning probe microscopy (SPM) study of a free-standing graphene membrane. The device was fabricated from a graphene flake exfoliated over an array of 1$\mu $m holes etched in SiO$_{2}$/Si substrate. Electronic spectra of both suspended and supported regions of single-layer graphene can be probed using SPM in a perpendicular magnetic field and in varying back gate voltages applied to the Si substrate. The significant differences found in electronic spectra of suspended and non-suspended graphene will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J37.00006: Quantized Landau level spectrum and its density dependence in graphene supported by SiO$_{2}$ Adina Luican, Guohong Li, Eva Andrei Scanning tunneling microscopy and spectroscopy in magnetic field was used to study Landau quantization in graphene and its dependence on charge carrier density. Measurements were carried out on exfoliated graphene samples deposited on a chlorinated thermal SiO$_{2}$ which allowed observing the Landau level sequence characteristic of single layer graphene while tuning the carrier density through the Si back-gate. Upon changing the carrier density we find abrupt jumps in the Fermi level after each Landau level is filled. Moreover, at low doping levels a marked increase in the Fermi velocity is observed which is consistent with the logarithmic divergence expected due to the onset of many body effects close to the Dirac point. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J37.00007: The effect of the tip in scanning tunneling spectroscopy of graphene Landau levels Kevin Kubista, David Miller, Ming Ruan, Walt de Heer, Phillip First, Gregory Rutter, Joseph Stroscio Landau Level (LL) spectroscopy measurements were performed on multilayer epitaxial graphene using 4 K scanning tunneling spectroscopy in magnetic fields up to 8 T. Fits of the LL energies to the form expected for graphene show a slight difference in the Fermi velocity of hole and electron states. We show that this may be a consequence of the work function difference between graphene and the tip material (iridium). Data sets consisting of LL energies versus magnetic field are used to fit a model tip potential. The calculated spectrum of tip-perturbed LLs reveals the possible source of some ``extra'' peaks. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J37.00008: Scanning tunneling spectroscopy of adsorbates and vacancies on graphene Jyoti Katoch, Masa Ishigami Adsorbates and vacancies sensitively influence transport properties of graphene. We have investigated the impact of adsorbates, such as atomic hydrogen and potassium, and vacancy defects on electronic properties of graphene at atomic scale using scanning tunneling microscopy and spectroscopy Our results will be discussed in comparison with previous transport measurements to understand the effect of extrinsic disorder on transport properties of graphene. [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J37.00009: A Scanning Tunneling Microscopy and Spectroscopy Study of K-doped Graphene Jeonghoon Ha, Hongwoo Baek, Beomyong Hwang, Minjun Lee, Jungseok Chae, Young Kuk Understanding the role of impurity scattering is crucial in explaining the carrier transport phenomena in a graphene device. Although unique two-dimensional Dirac fermion behavior have been confirmed by many transport experiments, direct observation of the local electronic structure around impurities may provide detailed picture of carrier scattering. In this study the local electronic structure of potassium deposited graphene film were studied using scanning tunneling microscopy (STM) and spectroscopy (STS). Chemical vapor deposition (CVD) graphene were transferred on a SiO$_{2}$ substrate after confirming the thickness and flatness by Raman spectroscopy and atomic force microscopy. STM images show relatively long-range screening around K impurities and the spatially resolved STS revealed unique electronic structure within the screening range. It was found that the screen range varies with the applied back gate bias, suggesting carrier density dependence. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J37.00010: Scanning Tunneling Microscopy Study of Fluorinated Graphene on Copper Scott Schmucker, Joshua Wood, Rick Haasch, Joseph Lyding We probe by ultrahigh vacuum scanning tunneling microscopy (UHV-STM) the structural and electronic properties of monolayer fluorinated graphene (C$_{x}$F, x$\approx $4) synthesized by chemical vapor deposition on copper substrates and fluorinated by xenon difluoride gas [1]. The chemical composition and structure of the resulting film is probed by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and scanning tunneling spectroscopy (STS). In contrast to metallic graphene, this material exhibits a large ($>$3 eV) band gap with a muted gap state corresponding to a copper surface state near -0.4 eV. We further investigate by STM alignment between the fluorographenic surface layer and copper substrate, uniformity of fluorination, and stability of fluorinated graphene under electron bombardment and thermal annealing.\\[4pt] [1] J.T. Robinson, et al., Nano Lett. 10, 3001-2005 (2010) [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J37.00011: Scanning tunneling spectroscopy of chemical vapor deposition grown graphene Daniel Cormode, Collin Reynolds, Brian LeRoy The electronic properties of CVD grown graphene were investigated by scanning tunneling microscopy. Mono and multi layered samples were prepared by growth on copper and transferred to 300 nm SiO$_2$ substrates. Raman spectroscopy mapping was used to determine the thickness of the samples as well as characterize regions of higher disorder as evidenced by an increased D peak. The samples were then measured in ultra high vacuum by scanning tunneling spectroscopy at 5 K. The type and density of defects measured with the STM were compared with measured D peak intensity. We have examined the correlation between changes in the local density of states and disorder in monolayer graphene. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J37.00012: Directed Assembly of Iron Phthalocyanine and Pentacene Molecules on a Graphene Monolayer Grown on Ru(0001) Shixuan Du, H.G. Zhang, J.T. Sun, L.Z. Zhang, Q. Liu, J.H. Mao, Y. Pan, M. Gao, H.T. Zou, H.M. Guo, W.A. Hofer, H.-J. Gao Monolayer graphene was successfully fabricated on 4$d $transition metal surfaces. The resulting ordered Moir\'e pattern was found to be an ideal template for the formation of ordered nanoclusters and molecules. Using scanning tunneling microscopy we show the selective adsorption process and assembly of iron phthalocyanine and pentacene molecules with different structural symmetries on a graphene monolayer, epitaxially grown on Ru(0001). The combination of first principles calculations and experimental measurements suggests that the lateral dipole field is the main driving mechanism for assembling molecules into ordered arrays. These findings should be important for achieving a large scale well-defined molecule-graphene interface. And such a detailed understanding of the molecular assembly will be essential in the actual fabrication process. [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J37.00013: Ab initio scanning tunneling spectroscopy simulation of graphene with metal adatoms: weak and strong coupling regimes Gunn Kim, Jae-Hyeon Parq, Jaejun Yu, Young-Kyun Kwon Metal atoms on graphene, when ionized, can act as a point-charge impurity to probe a charge response of graphene with the Dirac cone band structure. To understand charge and spin polarization in graphene, we present scanning tunneling spectroscopy STS simulations based on density-functional theory calculations. We find that a Cs atom on graphene is fully ionized with a significant band-bending feature in the STS whereas the charge and magnetic states of Ba and La atoms on graphene appear to be complicated due to orbital hybridization and Coulomb interaction. By applying external electric field, we observe changes in charge donations and spin magnetic moments of the metal adsorbates on graphene. [Preview Abstract] |
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