Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J36: Focus Session: Graphene Growth, Characterization and Devices: SiC and Metal Substrates |
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Sponsoring Units: DMP Chair: Kurt Gaskill, Naval Research Laboratory Room: C142 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J36.00001: SiC structuring and step bunching for C-face epitaxial graphene growth John Hankinson, Yike Hu, Ming Ruan, Baiqian Zhang, Claire Berger, Walt de Heer Recent research at Georgia Tech has focused on understanding and improving the epitaxial graphene growth process. Electronic experiments have demonstrated the excellent properties that high quality epitaxial graphene can posses when grown by the confinement controlled sublimation (CCS) method in an induction furnace [1]. Here we focus on the mechanisms at work in the early stages of graphitization. Experimental observations of C-face epitaxial graphene growth have revealed that when step-pinning defects are present they seem to act as preferential graphene nucleation sites. In addition we have observed preferential graphene growth on silicon carbide sidewalls and mesas. Ongoing work seeks to take advantage of the correlation between silicon carbide structure and graphene growth by pre-patterning the SiC substrate in order to better control the graphene grown on it. With CCS growth we have created flat graphene regions extending over tens of microns with RMS roughness below 2.5 angstroms. Growth results and electronic measurements on graphene grown on structured SiC mesas will be presented. \\[4pt] [1] R. Ming et al. Materials Science and Engineering -- Reports (submitted) [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J36.00002: Novel epitaxy of graphene using substrate microfabrication Hirokazu Fukidome, Masato Kotsugi, Takuo Ohkouchi, Toyohiko Kinoshita, Thomas Seyller, Karsten Horn, Yusuke Kawai, Maki Suemitsu, Yoshio Watanabe Epitaxy of graphene on SiC is promising for device applications owing to the capability to produce large-area film. For the further applications toward integrated devices, the microscopic thickness variation of graphene should be minimized because the thickness of graphene critically determines the electronic properties, such as carrier mobility and bandgap. One of the effective solutions is the epitaxy on microfabricated substrates to spatially control surface reactions involved in the epitaxy. The controllability of the epitaxy using substrate microfabrication has been already proven for the homoepitaxy on microfabricated Si substrates. We therefore study heteroepitaxy of graphene on microfabricated 6H-SiC(0001) substrates as a model system to produce epitaxial graphene without thickness variation. It has been in fact demonstrated by using photoemission and low energy electron microscopies that the epitaxial graphene exhibits no thickness variation when the size of microfabrication pattern is small (below 10 micrometer). Further the shape of the microfabrication pattern is also influential to the microscopic variation of the graphene. The controlled epitaxy of graphene by substrate microfabrication is thus demonstrated to be vital for future integrated graphene devices. [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J36.00003: Selective Epitaxial Graphene Growth on SiC via AlN Capping Farhana Zaman, Miguel Rubio-Roy, Michael Moseley, Jonathan Lowder, William Doolittle, Claire Berger, Rui Dong, James Meindl, Walt de Heer Electronic-quality graphene is epitaxially grown by graphitization of carbon-face silicon carbide (SiC) by the sublimation of silicon atoms from selected regions uncapped by aluminum nitride (AlN). AlN (deposited by molecular beam epitaxy) withstands high graphitization temperatures of 1420$^{o}$C, hence acting as an effective capping layer preventing the growth of graphene under it. The AlN is patterned and etched to open up windows onto the SiC surface for subsequent graphitization. Such selective epitaxial growth leads to the formation of high-quality graphene in desired patterns without the need for etching and lithographic patterning of graphene itself. No detrimental contact of the graphene with external chemicals occurs throughout the fabrication-process. The impact of process-conditions on the mobility of graphene is investigated. Graphene hall-bars were fabricated and characterized by scanning Raman spectroscopy, ellipsometry, and transport measurements. This controlled growth of graphene in selected regions represents a viable approach to fabrication of high-mobility graphene as the channel material for fast-switching field-effect transistors. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J36.00004: Multi-Layer Epitaxial Graphene Formed from Poly-Crystalline Silicon Carbide Grown on C-Plane Sapphire Timothy McArdle, Jack Chu, Yu Zhu, Zihong Liu, Mahadevaiyer Krishnan, Chris Breslin, Christos Dimitrakopoulos, Robert Wisnieff, Alfred Grill Growth of epitaxial graphene on substrates as large as eight inches in diameter is of great interest for integration with current CMOS technology. We use ultra-high vacuum chemical vapor deposition to grow poly-crystalline silicon carbide (SiC) on c-plane sapphire wafers, which are then annealed at high temperature in vacuum to create multi-layer epitaxial graphene films. Despite the roughness and small domain size of the poly-crystalline SiC films, a thick, conformal layer of graphene is formed. Reducing the surface roughness by chemical-mechanical polishing the SiC surface prior to the anneal results in a dramatic reduction of the Raman defect band observed in the final graphene film. Additionally, the graphene formed on polished SiC demonstrates significantly more ordered layer-by-layer graphene growth and increased carrier mobility for the same carrier density as the unpolished samples. [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J36.00005: Theory of the Growth of Epitaxial Graphene on Silicon Carbide Fan Ming, Andrew Zangwill We present a one-dimensional kinetic Monte Carlo model for the growth of epitaxial graphene on 6H-SiC. The model parameters are effective energy barriers for the nucleation and subsequent propagation of graphene at step edges. For growth on vicinal substrates with half-unit-cell height steps, we predict first and second layer graphene coverages and the distribution of first-layer graphene strip widths as a function of total coverage, vicinal angle, and the model parameters. Comparing our results to experiment will provide the first quantitative insights into the kinetics of growth for this unusual epitaxial system. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J36.00006: A density-functional theory study for the mobility of carbon atoms on 6H SiC(0001) Christian Ratsch Graphene is a very promising material for many microelectronic applications because of its unique electronic properties. Among the several proposed routes to fabricate (single) layers of graphene, the growth of epitaxial graphene on 4H and 6H SiC(0001) appears to be particularly promising. The 6H SiC(0001) surface has 3 different polytypes. In this talk, results from density-functional theory calculations will be presented for the potential energy surfaces and different diffusion rates of C atoms on these different polytype surfaces. Both, the Si or C terminated surfaces will be investigated. Results for the adsorption of single and multiple graphene layers will also be presented. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 1:03PM |
J36.00007: Epitaxial graphene on SiC(0001) Invited Speaker: Epitaxial graphene on SiC is considered to open a route towards graphene based electronics such as, e.g., high frequency transistors. Recently considerable progress has been made in the growth of epitaxial graphene on SiC. On the Si-face of SiC, where the growth is slower as compared to the C-face, monolayers can be grown reliably. However, several open questions remain. Transport studies as well es photoelectron spectroscopy has shown that the pristine layers on SiC(0001) are heavily electron doped ($n=1\times10^{13}$~cm$^{-1}$). This results in rather low electron mobilities of the order of 2000~cm$^2$/Vs at 25~K. In addition, the carrier mobility shows a strong temperature dependence so that it drops to around 1000~cm$^2$/Vs at 300~K. In my presentation I will first show how chemical gating of graphene by deposition of F4TCNQ affects the carrier mobility. Hall effect measurements on samples close to charge neutrality show a carrier mobility of 29,000~cm$^2$/Vs at 25~K. Then I will discuss measurements demonstrating inertial-ballistic transport in nanoscale cross junctions fabricated from epitaxial graphene on SiC(0001). Finally, I will review recent results obtained by hydrogenation of the interface between graphene and SiC(0001). The latter process leads to a decoupling of the bufferlayer which is converted into quasi-freestanding graphene (QFMLG). The electronic, structural, and transport properties of QFMLG will be discussed in detail. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J36.00008: Structural and Electronic Properties of Graphene on Cu(111) and SiC(0001) Li Gao, Paolo Sessi, Jongweon Cho, Jeffrey R. Guest, Nathan P. Guisinger Graphene has shown attractive physical properties and is a promising new material. The structural and electronic properties of graphene on Cu(111) and SiC(0001) have been investigated by scanning tunneling microscopy and spectroscopy and Raman spectroscopy. The growth of graphene on these two substrates was achieved by thermal decomposition of ethylene on Cu(111) and thermal decomposition of SiC(0001) surface, respectively, in an ultra high vacuum chamber. On Cu(111), the nucleation of monolayer islands and two predominant domain orientations have been observed, which leads to the formation of numerous domain boundaries with increasing coverage [1]. Raman spectroscopy verifies the single layer thickness and shows the defect-induced bands for graphene on Cu(111). On SiC(0001), the electronic structure of the first two carbon layers on top of the $6\sqrt 3$ surface reconstruction has been studied by scanning tunneling spectroscopy. \\[4pt] [1] L. Gao, J. R. Guest, and N. P. Guisinger, Nano Lett. 10, 3512 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J36.00009: Wafer scale synthesis of bilayer graphene film Kyunghoon Lee, Seunghyun Lee, Zhaohui Zhong The discovery of electric field induced bandgap opening in bilayer graphene paves the way for making semiconducting graphene without aggressive size scaling, or using expensive substrates. Despite intensive research, synthesizing homogeneous bilayer graphene in large size has proven extremely challenging, and the size of bilayer graphene was limited to micrometer scale by exfoliation Here we demonstrate homogeneous bilayer graphene films over at least square inch area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. Bilayer coverage of over 99{\%} is confirmed by spatially resolved Raman spectroscopy. The result is further supported by electrical transport measurements on bilayer graphene transistors with dual-gate configuration, where field induced bandgap opening is observed in 98{\%} of the devices. The size of our bilayer graphene film is only limited by the synthesis apparatus and can be readily scaled up, thus enabling wafer scale graphene electronics and photonics. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J36.00010: Visualizing graphene grown by chemical vapor deposition on metal substrates at the atomic scale Liuyan Zhao, Kwang Rim, Christopher Gutierrez, Rui He, Keunsoo Kim, Hui Zhou, Tony Heinz, Philip Kim, Aron Pinczuk, George Flynn, Abhay Pasupathy We present an atomic-scale scanning tunneling microscopy (STM) study of large-area graphene films grown by chemical vapor deposition (CVD) on metal substrates. We will first describe experiments where pristine graphene is grown in UHV conditions on single crystal Cu(111) and Cu(100) surfaces. We will compare this with graphene grown on copper foils and thin films in a typical low-pressure tube furnace. We will describe the effect of substrate quality and orientation on the quality and electronic structure of the graphene film produced. Finally, we will describe experiments where the graphene film is doped by nitrogen during growth. We will describe the bonding environment and the local electronic structure caused by the incorporation of nitrogen atoms into the graphene lattice. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J36.00011: Graphene Growth and Defects on Ni(111) Matthias Batzill, Jayeeta Lahiri Using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) we have investigated the growth of graphene on Ni(111) surfaces by carbon segregation from the bulk. We reveal two distinct growth modes for graphene growth. Between 480 and 650 C graphene forms on clean Ni(111) and below 480 C graphene grows by an in-plane conversion of a surface carbide phase. This is the first time that graphene formation is observed by transformation of a surface carbide. STM indicates that a lattice-matched, one-dimensional in-plane domain boundary between graphene and the carbide forms and graphene grows by replacing Ni-atoms with carbon at this interface. In addition to the growth of graphene we will also briefly discuss atomic-scale defects that can be synthesized in Ni-supported graphene. In particular we emphasize the formation of an extended line-defect with metallic properties [1]. \\[4pt] [1] J. Lahiri, Y. Lin, P. Bozkurt, I.I. Oleynik, M. Batzill Nature Nanotechnol. 5, 326 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J36.00012: Atomic Structures and Electronic Scattering of Graphene Edges Jifa Tian, Helin Cao, Jongweon Cho, Li Gao, Jeffrey R. Guest, Nathan P. Guisinger, Wei Wu, Qingkai Yu, Yong P. Chen The success of growing monolayer gaphene on Cu foils has stimulated intense interests to study its structural and electronic properties at the atomic scale. Here we present a scanning tunneling microscopy (STM) investigation on single crystalline graphene islands synthesized on polycrystalline Cu foils by chemical vapor deposition (CVD). Our studies reveal that most of the graphene edges are macroscopically parallel to the zigzag directions with microscopic roughness. The observed rough edges follow the zigzag directions at atomic scale and make many 120-degree turns. Strong electron scattering was observed from a rarely-occurring armchair-oriented edge, and there is little such scattering observed from zigzag-oriented edges. In addition, we also observed nearly periodic parallel lines attributed to the surface dislocations of the Cu underneath graphene. [Preview Abstract] |
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