Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A17: Graphene: Growth and SynthesisFocus
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Sponsoring Units: DMP Chair: Joshua Robinson, Pennsylvania State University Room: 316 |
Monday, March 14, 2016 8:00AM - 8:36AM |
A17.00001: Materials Science and Engineering with Two-dimensional Atomic Layers Invited Speaker: Pulickel M. Ajayan There has been tremendous interest in recent years to study two-dimensional atomic layers which form building blocks of many bulk layered materials and devices. This talk will focus on the materials science aspects of 2D atomic layer, in particular the emerging structures based on transition metal chalcogenides. Several aspects that include synthesis, characterization and device fabrication will be explored with the objective of achieving all 2D functional structures for future technologies. The concept of nanoscale engineering and the goal of creating new artificially stacked van der Waals solids will be discussed through a number of examples. The challenges involved in scalable synthesis, doping, defect engineering, surface modifications of monolayers and the controlled creation of stacked structures and in-plane junctions from multiple compositions will be discussed. Some of anticipated applications of these materials will also be discussed. [Preview Abstract] |
Monday, March 14, 2016 8:36AM - 8:48AM |
A17.00002: Large area single crystalline graphene growth on copper foil Jaehyuck Jung, Hoang Danh Phan, Lee Changgu Graphene synthesis methods using chemical vapor deposition (CVD) have been developed dramatically in these years but still it is challenging to make large size single crystal grains which have similar properties with pristine graphene. Here we report a pita-pocket method of growing large area single crystalline graphene on copper foil. We made holes on top of the closed copper pocket to provide stable gas flow inside of pocket, and copper domains with (111) crystal orientation, which gives an advantage for hexagonal graphene crystal growth, were formed continuously during synthesis. Liquid crystal analysis and electron backscatter diffraction (EBSD) were used to observe the copper crystallographic orientation. Also we compared with a traditional pocket method and an opened flat copper foil method. Graphene from the other methods had poly-crystalinity with different orientation in contrast to graphene from the hole-pocket method. [Preview Abstract] |
Monday, March 14, 2016 8:48AM - 9:00AM |
A17.00003: Strain-Engineering the Gauge Potential of Dirac fermions in PECVD-grown Graphene Chen-Chih Hsu, Marcus Teague, Jaiqing Wang, Nai-Chang Yeh Non-trivial strain can induce pseudo-magnetic fields in graphene so that the electronic properties of Dirac fermions can be tuned by controlling the strain on graphene. Here we employ nearly strain-free single-domain PECVD-graphene$^{\mathrm{1}}$ to induce controlled strain by placing graphene on nanostructured substrates. Strain-induced gauge potentials and pseudo-magnetic fields can be manifested by the local tunneling conductance peaks at quantized energies.$^{\mathrm{2,3}}$ Additionally, pseudo-magnetic field-induced local spontaneous time-reversal symmetry breaking can be revealed by spatially alternating presence and absence of the zero mode in the tunneling conductance spectra.$^{\mathrm{2,3}}$ We also employ molecular dynamics simulations to determine the spatial distribution of the pseudo-magnetic field for a given nanostructure. We find that a tetrahedron-like nanostructure can be an effective “valley splitter” to separate the trajectories of Dirac fermions of opposite pseudo-spins. Proper design and arrangement of several valley filters can function as a “valley propagator” to guide valley-polarized currents. We plan to verify the valley Hall effect associated with a valley splitter and to assess the feasibility of realistic valleytronic applications. 1. D.A. Boyd et al. Nat. Comm. 6, 6620 (2015). 2. N.-C. Yeh et al. Surface Science 605, 1649-1656 (2011). 3. N.-C. Yeh et al. Acta Mechanica Sinica (in press). [Preview Abstract] |
Monday, March 14, 2016 9:00AM - 9:12AM |
A17.00004: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 9:12AM - 9:24AM |
A17.00005: SPALEED Studies of~the Growth of Zero to Mono-layer Graphene on SiC(0001) M. Hupalo, M. T. Hershberger, H. Hattab, D. C. McDougall, M. Horn von Hoegen, M. C. Tringides The growth of graphene on SiC was studied in detail with SPA LEED to understand the transition from zero to monolayer graphene with increasing temperature starting at 1200\textdegree C. Both the changing diffraction spots with annealing and their line shapes are studied in detail until a fully completed monolayer is obtained with only 6x6 spots remaining. In particular we focus on two strong features not investigated previously: (i) superstructures spots at n/13 locations present between the specular and the graphene spots. These spots are possibly related to different coincidence lattices before graphene locks into its final 6x6 orientation. (ii) The presence of a very broad background intensity covering \textasciitilde 60{\%} of the BZ both around the specular and graphene spots whose origin is still unknown. Detailed studies of the dependence of this background component on energy and comparison between the graphene and specular spots suggest that the origin is not due to the standard variation with electron energy, i.e. a g(s) curve caused by the topography. Throughout the literature this broad background has been seen in graphene grown in different types of substrates. We comment on possible reasons for the origin of the background. [Preview Abstract] |
Monday, March 14, 2016 9:24AM - 9:36AM |
A17.00006: Growth of Graphene on Cu Single Crystal Substrates Tyler Mowll, Eng Wen Ong, Parul Tyagi, Zachary Robinson, Carl Ventrice A common technique for synthesizing single-layer graphene films is CVD on Cu foil substrates. However, the presence of crystalline defects in the CVD graphene films results in a reduction in the transport properties. In order to achieve a better understanding of the influence of the surface termination of the Cu substrate on the crystallization of graphene during the CVD process, a systematic study of graphene growth on Cu(100), Cu(110), and Cu(111) crystals has been performed. The graphene synthesis is done in a UHV chamber that has been modified to perform graphene growth at pressures as high as 100 mTorr. The precursor gas used is ethylene. This growth procedure allows for the preparation of the clean Cu surfaces in UHV, growth under typical CVD conditions, and characterization of the graphene in UHV, without exposing the sample to atmospheric contaminants. Our results indicate that the surface termination of the Cu substrate has a strong influence on the decomposition rate of the ethylene and the rotational alignment of the graphene grains as they nucleate on each surface. For Cu(111), single-domain graphene growth can be achieved for ethylene pressures of 5 mTorr or less. For both Cu(100) and Cu(110), a minimum of two graphene domains is always observed. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A17.00007: Strain sensing through the optical properties of graphene: Comparing indentation of epitaxial- and CVD-grown graphene Erin L. Wood, Yanfei Yang, Will Gannett, Gordon A. Shaw, Randolph E. Elmquist, Mark W. Keller, Angela R. Hight Walker The unprecedented mechanical and electrical properties of graphene have garnered great interest, yet critical understanding of deformation processes is needed before robust devices are realized. Raman spectroscopy is an information rich, non-destructive probe of mechanical, structural, and electrical properties of graphene through analysis of the prominent bands; D, G, and G'. Previous reports on strained graphene have been largely limited to graphene transferred to flexible substrates and have produced divergent results regarding shifting and splitting in the G band. To systematically evaluate strain, we compare as-grown graphene on either Cu or SiC to the blank substrates which are well understood. Strain was applied by micro- or nano-indentation and Raman mapping was collected of the deformed area providing validation of the applied strain. Confocal Raman microscopy is diffraction limited, however, and localized strain cannot be spatially resolved at the nanoscale. To overcome this, an AFM probe was co-located within the Raman laser focus to obtain sub-diffraction spatial resolution. This also increases the sensitivity to the surface, allowing for observation of the D peak within a micron of nano-indents, which was unseen in confocal Raman spectroscopy. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A17.00008: Oxygen-Activated Growth and Bandgap Tunability of Large Single-Crystal Bilayer Graphene Yufeng Hao, james hone, rodney ruoff, Luigi Colombo Distinct from zero-bandgap single-layer graphene, Bernal-stacked bilayer graphene (BLG) is a semiconductor whose bandgap can be tuned by a transverse electric field, making it a unique material for a number of electronic and photonic devices. In this presentation, we will focus on the most recent progress in the identification of new growth mechanisms towards large-area single-layer BLG on Copper: multiple control experiments and first-principles calculations are used to support the proposed mechanisms. We emphasize that trace amount of impurities on metal surface are critical to initiate graphene growth and affect the growth kinetics. Furthermore, contrary to the traditional viewpoint that graphene growth is always surface-limited process, our new observations strongly suggest that metal bulk plays a role to feed carbon species for graphene growth. State-of-the-art structural characterizations and electrical transport measurements of the CVD graphene layers will be presented as well. [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A17.00009: In-Situ Measurements of Graphene Mechanics During Annealing Aaron Hui, Roberto De Alba, Abhilash Sebastian, Jeevak Parpia Graphene shows great potential as a material for a new generation of mechanical nanodevices. However, current methodologies used for fabricating graphene structures involve polymer resists for transfer and patterning, which degrades mechanical performance. To improve surface quality, high current or high temperature annealing of graphene is commonly employed. Previous studies of graphene mechanics have focused on performance after annealing or temperature-dependent behavior from 4K-300K. Here we present real-time, in-situ measurements of graphene mechanical resonance during high temperature annealing from 300K-600K. Upon heating, reversible changes in mechanical frequency are indicative of graphene thermal contraction. Discontinuous and irreversible changes are also seen, corresponding to graphene slipping and mass desorption. Both reversible and irreversible changes in quality factor are also observed. Characterizing the effects of annealing on the structural properties of graphene will enable more precise engineering for particular applications, such as mass sensing. [Preview Abstract] |
Monday, March 14, 2016 10:12AM - 10:24AM |
A17.00010: Effective structural properties in polycrystalline graphene Zubaer Hossain This talk will discuss effective structural properties in polycrystalline graphene under the presence of atomic scale heterogeneity. Polycrystallinity is ubiquitous in solids, but theories describing their effective behavior remain limited, particularly when heterogeneity is present in the form of nonuniform deformation or composition. Over the decades, exploration of the effective transport and strength properties of heterogeneous systems has been carried out mostly with random distribution of grains or regular periodic structures under various approximations, in translating the underlying physics into a single representative volume element. Although heterogeneity can play a critical role in modulating the basic behavior of low-dimensional materials, it is difficult to capture the local characteristics accurately by these approximations. Taking polycrystalline graphene as an example material, we study the effective structural properties (such as Young's Modulus, Poisson's ratio and Toughness) by using a combination of density functional theory and molecular dynamic simulations. We identify the key mechanisms that govern their effective behavior and exploit the understanding to engineer the behavior by doping with a carefully selected choice of chemical elements. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A17.00011: Pump-induced far-infrared reflection in quasi-intrinsic graphene Martin Mittendorff, Ryan J. Suess, Thomas E. Murphy, Harald Schneider, Manfred Helm, Stephan Winnerl We present an experimental far-infrared pump-probe study on multilayer epitaxial graphene that is complemented by a straightforward theoretical model. To gain deeper insights into the pump-induced change in the complex conductivity in the far-infrared, pump-probe measurements recording both transmission and reflection were performed. These measurements reveal a pump-induced increase of the transmission at low pump fluence, and a decreased transmission at high pump fluence due to a strong pump-induced reflection. Modelling the temperature dependent conductivity for interband and intraband processes in combination with an energy balance equation reproduces the observed results. [Preview Abstract] |
Monday, March 14, 2016 10:36AM - 10:48AM |
A17.00012: Atomic intercalation -- a practical method to determine the nanoscale adhesion energy of graphene on HOPG Jun Wang, Dan Sorescu, Seokmin Jeon, Alexei Belianinov, Sergei Kalinin, Arthur Baddorf, Petro Maksymovych A detailed analysis of atomic intercalates in graphite provides a direct estimate of the nanoscale elastic adhesion of a graphene sheet atop highly ordered pyrolytic graphite (HOPG). Atomic intercalation is carried out using conventional ion sputtering, creating ``blisters'' in the top-most layer of the HOPG surface. Scanning tunneling microscopy coupled with image analysis and density functional theory is used to reconstruct the atomic positions and the strain map within the deformed graphene sheet. To estimate the adhesion energy we invoke an analytical model originally devised for macroscopic deformations of graphene. This model yields a value of is 0.221 \pm\ 0.011 J/m$^{\mathrm{2}}$ for the adhesion energy of graphite, which is in surprisingly good agreement with reported experimental and theoretical values. This implies that mechanical properties of graphene scale at least to lengths of a few nanometers. The simplicity of our method enables analysis of elastic mechanical properties in many two-dimensional layered materials and provides a unique opportunity to investigate the local variability of mechanical properties on the nanoscale. [Preview Abstract] |
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