Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D28: Focus Session: Graphene Growth, Characterization, and Devices: Metal Substrates |
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Sponsoring Units: DMP Chair: Kevin McCarty, Sandia National Laboratory Room: C156 |
Monday, March 21, 2011 2:30PM - 2:42PM |
D28.00001: Theory of the Growth of Epitaxial Graphene on Close-Packed Metals Andrew Zangwill, Dimitri Vvedensky We present a simple rate theory of epitaxial graphene growth on close-packed metals. Motivated by recent low-energy electron microscopy experiments [E. Loginova, N.C.Bartelt, P.J. Feibelman, and K.F. McCarty, New Journal of Physics, {\bf 10}, 093026 (2008)], our theory supposes that graphene islands grow predominantly by the addition of five-atom clusters, rather than solely by the capture of diffusing carbon atoms. With suitably chosen kinetic parameters, we find quantitative agreement with (i) the measured time-evolution of the adatom density and (ii) the measured temperature-dependence of the adatom density at the onset of nucleation by assuming that the smallest stable precursor to graphene growth is an immobile island composed of six five-atom clusters. [Preview Abstract] |
Monday, March 21, 2011 2:42PM - 2:54PM |
D28.00002: Graphene Growth on Cu Surface: A Theoretical Study Zhenyu Li, Ping Wu, Wenhua Zhang, Jinlong Yang, J. G. Hou Graphene is an important material with many unique properties and a great application potential. A promising way to produce wafer-size graphene is chemical vapor deposition (CVD) on metal surfaces. To improve sample quality, it is important to understand the atomic details during graphene CVD growth. In this talk, some relevant elementary processes on Cu surface have been studied from first principles. Although diffusion of atomic carbon on Cu (111) surface is almost barrierless, coalescence of carbon atoms on the surface is found to be hampered by an intermediate bridging-metal structure. The fact which makes things more complicated is that thermodynamic analysis indicates that the main species on the Cu surface during graphene growth is not the simplest atomic carbon. Therefore, CxHy species should be explicitly considered for initial stage growth of graphene on Cu surface. [Preview Abstract] |
Monday, March 21, 2011 2:54PM - 3:06PM |
D28.00003: Graphene Made Easy: A Simple Method to Grow Large-Area Single-Layer Graphene on Copper Foils S. Gadipelli, I. Calizo, J. Ford, G. Cheng, A. H. Walker, T. Yildirim In order to realize the remarkable properties of graphene in practical devices, an easy, scalable, and inexpensive synthesis method is necessary. Currently the most promising approach is through chemical vapor deposition (CVD). However, this method requires expensive CVD furnaces and flow controllers, as well as a large amount of explosive gases (H$_{2}$ and CH$_{4})$. Consequently, it is desirable to establish alternative methods to grow large-area, single-layer graphene that are simple and that can be carried out in an ordinary research laboratory. In this talk, we will discuss our systematic study of the parameters that are critical for high-quality, single-layer graphene formation. Our results not only shed light on the graphene growth mechanism, but have also yielded a straightforward synthesis method that requires neither H$_{2}$/CH$_{4}$ nor any special CVD equipment. We have prepared graphene samples at the inch scale that have been characterized by Raman spectroscopy, optical transmittance, and sheet resistance measurements. Our method is simple, safe, and economical and will be of value to both fundamental researchers and nanodevice engineers. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:42PM |
D28.00004: Graphene on metals - structure and properties Invited Speaker: The ``metal route'' to graphene, i.e., the epitaxial growth of graphene on a metal surface by chemical vapor deposition (CVD) of hydrocarbon molecules and the following transfer of the graphene film to an insulating support, has recently made great progress [see, e.g., S. Bae et al., Nature Nanotechnol. 5, 574 (2010)]. However, structurally and from their charge carrier mobilities, metal-grown graphene samples have not yet reached the quality of exfoliated graphene, most likely resulting from uncontrolled processes during the CVD. In order to better understand how graphene interacts with metal surfaces we have performed a series of surface science studies. As experimental techniques we have applied STM, ARPES, LEED, and SXRD, mainly on Ru(0001)/graphene, and we have performed extensive DFT analyses. We find a short metal-graphene separation, a strong deformation of the graphene, a lifting of the Dirac point, and shifts of the electronic bands. The structural and electronic properties evidence surprisingly strong interactions of the graphene with the Ru surface which are probably prototypical for other metals such as Co, Ni, and Pd. A second group of metals, namely Ir, Pt, Cu, Ag, and Au, only show weak interactions. In situ STM experiments at high temperatures (between 380 and 780 C) show that the usual ``carpet mode'' by which graphene grows across steps of the metal surface [P. W. Sutter et al., Nature Mater. 7, 406 (2008)] can lead to defects. However, the growth mode changes at high temperatures and low pressures of the hydrocarbon precursor, partially a result of the relatively high Ru-graphene interactions. They lead to a faceting of the surface, and one can grow extremely large single-crystalline graphene films on single terraces in this way. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 3:54PM |
D28.00005: Second-layer graphene growth from below on metals Shu Nie, Elena Starodub, Norman Bartelt, Kevin McCarty Once a metal substrate is covered by the first graphene layer, CVD processes slow greatly. However, C dissolved in the metal can still segregate to the surface under the first graphene layer. To determine whether these C atoms nucleate a new layer below or above the first layer, we examine growth on Ir(111), where one-layer graphene has several discrete in-plane orientations relative to substrate directions. LEED reveals that the 1st and 2nd graphene layers are not always rotationally aligned in-plane. This misalignment allows determining which sheets are on the top and the bottom by varying the electron energy and thus the escape depth. We first use LEEM to determine the spatial distribution of rotational domains in a single-layer film. We then cool and observe 2nd layer growth. We find that the top sheet of the bilayer has the exact same domain structure as the initially grown single layer. Thus, new layers are added from below. In this mechanism the nucleation and growth of the 2nd layer strongly depends on the difficulty in debonding the 1st layer from the substrate. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D28.00006: Low Temperature Graphene Growth by Down-Stream Chemical Vapor Deposition Lola Brown, Mark Levendorf, Chad Hunter, Jiwoong Park Integration of high quality graphene directly onto the surface of metal provides a novel way of controlling the functionality of metal surfaces. This can be used to control the chemical and physical surface interactions and enhance energy transfer through the surfaces, thus allowing for new sensors, flexible electronic devices and better electrodes for organic photovoltaics. However, the implementation of a pristine graphene layer in patterned devices is currently limited, due to the high temperature growth ($\sim $1000 C) and contamination of the graphene surfaces during transfer. This work presents graphene grown at low temperatures (below 750 C) using down-stream chemical vapor deposition (DS-CVD), where a metallic growth substrate is positioned down-stream from the CVD furnace ``hot zone''. High quality graphene is produced using long growth times ($\sim $ 60 minutes) and low gas flow rates. We study graphene quality and grain structure using Raman spectroscopy and dark-field transmission electron microscopy (DF-TEM). We demonstrate the strength of this technique by growing graphene on thin and micro patterned copper films, and three dimensional structures. [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D28.00007: Evolution of graphene islands growing on Cu foils Joseph Wofford, Shu Nie, Norman Bartelt, Kevin McCarty, Oscar Dubon Using low-energy electron microscopy we investigate, in real time, the growth of graphene monolayers on Cu foils. Graphene islands evolve from an initially compact form into an increasingly ramified, four-lobed shape, reflecting the symmetry of the (100)-textured Cu surface. Diffraction analysis reveals that each lobe is an individual graphene domain, differentiated by a rotation about the film normal, making the islands polycrystalline. An inspection of the morphological evolution of the graphene lobes shows the growth fronts posses an angularly dependent velocity, which is consistent with a growth mode dominated by edge kinetics. The fast growth direction of each lobe tends to align with the $<$001$>$ in-plane directions of the Cu surface but not with a high symmetry direction of the graphene lattice. Finally, the implications of this unexpected growth mechanism on the formation of high-quality graphene films on Cu foils are evaluated. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D28.00008: Characterization of Graphene Films Grown on Cu-Ni Foil by XPS P. Tyagi, R.L. Moore, Z.R. Robinson, C.A. Ventrice, Jr., D.D. Moody, W. Priyantha, R. Droopad, C. Magnuson, D. Munson, S. Chen, R.S. Ruoff Monolayer graphene films can be grown on Cu substrates by the catalytic decomposition of methane molecules. The solubility of carbon in Cu is negligible at the growth temperatures typically used for graphene growth, which results in the formation of films that self-terminate at a monolayer. In an attempt to enhance the catalytic activity of the surface, use of Cu-Ni alloy foils has been investigated. Growth is performed in a CVD system at a temperature of 1000~\r{ }C with pure CH$_{4}$. To determine the graphene coverage and the surface alloy composition during the different phases of growth, XPS measurements have been performed on the Cu-Ni foils before anneal, after anneal in H$_{2}$, and after growth of graphene. Analysis of the C-1s core emission for graphene/Cu is used as reference for monolayer growth. Before anneal, the measurements indicate that the surface is Ni-rich and heavily oxidized. After annealing in H$_{2}$, only a small amount of oxide remained and the Cu:Ni alloy fraction was similar to the bulk. After growth of the graphene overlayers, only trace amounts of oxygen are present, indicating uniform graphene growth. [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D28.00009: Effects of heat-treatment and hydrogen adsorption on Graphene grown on Cu foil Jongweon Cho, Li Gao, Jifa Tian, Helin Cao, Qingkai Yu, Jeffrey Guest, Yong Chen, Nathan Guisinger Graphene has recently been a subject of intense research efforts due to its remarkable physical properties as an ideal two-dimensional material. While numerous different methods for graphene synthesis are being explored, CVD-grown graphene on Cu foil presents the possibility of a large-scale and high-quality synthesis of graphene. [1] To improve the quality of graphene films on Cu foil prepared by CVD and better understand its microscopic growth, atomic-scale characterization becomes of great importance. We have investigated the effects of thermal annealing and hydrogen adsorption/desorption on \textit{ex-situ} CVD-grown monolayer graphene on polycrystalline Cu foil at the atomic-scale using ultrahigh vacuum scanning tunneling microscopy, and we will report on these studies. \\[4pt] [1] Li et al, Science \textbf{324}, 1312 (2009). [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D28.00010: Imaging Grains and Grain Boundaries in Single-Layer CVD Graphene P.Y. Huang, A.M. van der Zande, C.S. Ruiz-Vargas, W.S. Whitney, M.P. Levendorf, Y. Zhu, J. Park, P.L. McEuen, D.A. Muller Single-layer graphene can be produced by chemical vapor deposition (CVD) on copper substrates on up to meter scales [1, 2], making their polycrystallinity [3,4] almost unavoidable. By combining aberration-corrected scanning transmission electron microscopy and dark-field transmission electron microscopy, we image graphene grains and grain boundaries across five orders of magnitude. Atomic-resolution images of graphene grain boundaries reveal that different grains stitch together predominantly via pentagon-heptagon pairs. We use diffraction-filtered imaging to map the shape and orientation of several hundred grains and boundaries. These images reveal an intricate patchwork of grains with structural details depending strongly on growth conditions. These imaging techniques will enable studies on the structure, properties, and control of graphene grains and grain boundaries. \\[4pt] [1] X. Li et al., Science 324, 1312 (2009).\\[0pt] [2] S. Bae et al., Nature Nanotechnol. 5, 574 (2010).\\[0pt] [3] J. M. Wofford, et al.,Nano Lett., (2010).\\[0pt] [4] P.Y. Huang et al., arXiv:1009.4714, (2010). [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D28.00011: Analysis of Substrate Grain Size and Orientation on the Growth of Graphene Films Z.R. Robinson, P. Tyagi, T.M. Murray, C.A. Ventrice, Jr., C. Magnuson, D. Munson, S. Chen, R.S. Ruoff Graphene growth on Cu foils by catalytic decomposition of methane forms predominately single layer graphene films due to the low solubility of C in Cu. One of the key issues for the use of CVD graphene in device applications is the influence of defects on the transport properties of the graphene. For instance, growth on foil substrates is expected to result in multi-domain graphene growth because of the presence of randomly oriented grains within the foil. Therefore, the size and orientation of the grains within the metal foil should strongly influence the defect density of the graphene. To study this effect, we have initiated a study of the influence of pre-growth anneal time and H$_{2}$ pressure on the grain size and structure of Cu and Cu-Ni foil substrates. Preliminary measurements of the grain size have been performed with SEM and AFM. These results show a typical lateral dimension of $\sim $100 $\mu $m for an anneal time of 30 min in 40 mTorr of H$_{2}$ at 1000 \r{ }C. Measurements are currently being performed with electron backscatter diffraction to determine the crystallographic orientation within each grain. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D28.00012: Alloy substrates: towards precise control of thickness and quality of multilayer graphene growth Shanshan Chen, Weiwei Cai, Richard D. Piner, Xuesong Li, Yanwu Zhu, Rodney S. Ruoff Graphene has gained a lot of attention due to its remarkable properties, such as high electron hole mobility, high current carrying capability and high mechanical robustness. It has been further demonstrated that the properties of graphene materials depend on the number of graphene layers present. As a result, it is highly desirable to develop reliable synthesis techniques to synthesize few- or multi-layered high quality large area graphene materials. Here we report a facile method to grow few-layer graphene films using an alloy substrate by chemical vapor deposition. The thickness and quality of the graphene and graphite films can be controlled using CVD with methane and hydrogen gas as precursors, by varying the deposition temperature and cooling rate. The optical and electrical properties of the graphene/graphite films were studied as a function of their thickness. [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D28.00013: Improving Polycrystalline Copper Surface by Hydrogen Etching for Graphene Growth Merve Arseven, Tayfun Vural, Engin Ozdas Growth of high quality, large scale pattern of graphene is the main important phenomenon to use this material in novel technological applications. CVD methods can provide an effective way to produce graphene, however, require a rigid stable substrate at high temperature processes [1]. Besides, the substrate that can be used in these processes must have low solubility of carbon to obtain mono or few layers of graphene, and be able to provide bigger grains for a large-scale growth [2]. Polycrystalline copper foil is an appropriate candidate to achieve these attributions in case of reducing the pinhole and defect density, and increase the grain size. In this study, we investigate the effect of hydrogen partial pressure, heating rate, annealing temperature and duration on the etching process to optimize the surface. Surface roughness analyses are performed by AFM, and grain size distributions are determined by the analyses of optical microscope images. [1] Sukang Bae \textit{et al}., Nature Nanotechnology \textbf{5}, 574, 2010. [1] Xuesong Li \textit{et al}., Science \textbf{324}, 1312, 2009. [Preview Abstract] |
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