Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A30: Graphene: Structure, Defects, and FunctionalizationFocus
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Sponsoring Units: DMP Chair: Nathan Guisinger, Argonne National Laboratory Room: 293 |
Monday, March 13, 2017 8:00AM - 8:36AM |
A30.00001: Self-assembly of environmental adsorbates on graphene and other 2D materials Invited Speaker: Patrick Gallagher Graphene sheets on atomically flat substrates are expected to be flat. Yet recent studies of nominally flat graphene using high-resolution atomic force microscopy have revealed an apparently corrugated surface: topography scans show large-scale periodic structures of stripes whose period is 4 nm and whose amplitude can be a few tenths of a nanometer. I will present scanning probe and optical measurements that show that these stripes are self-assembled environmental adsorbates, the chemical identity of which is still under study. This self-assembly appears to be common on 2D materials, as the same phenomenon occurs on sheets of hexagonal boron nitride, and 4 nm-periodic stripes were recently observed on molybdenum disulfide by another group. I will discuss the impact of the self-assembled stripes on the frictional, optical, and electronic properties of graphene samples. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A30.00002: Templated Functionalization of Epitaxial Graphene Michael Bedzyk, Jonathan Emery, Gavin Campbell, Sumit Kewalramani, Justice Alaboson, Xiaolong Liu, Itamar Balla, Mark Hersam Nanoscale control and integration of disparate materials on graphene is a critical step towards the development of graphene-based electronics and sensors. Among different graphene substrates, epitaxial graphene (EG) on SiC provides several advantages for functionalization, including high electronic quality, tunable substrate coupling, wafer-scale processability, and crystalline ordering that can template commensurate growth. Exploiting the wafer-scale registry of EG on SiC to template self-assembly and heterostructure materials; we have demonstrated multiple avenues toward functionalization that each offer distinct modifications to the electronic and chemical properties of the underlying graphene. The local functionalized structure and electronic nature is revealed through scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The precise multi-length scale structure at and below the top surface layer is determined via simultaneous grazing incidence small- and wide- angle X-ray scattering (GISAXS/GIWAXS), which gives the relative orientations of the in-plane lattice vectors of the EG, SiC, and functionalized material. We used this scan-probe/X-ray scattering method to examine systems of epitaxial MoS2 and organically templated OPA nanowires on EG/SiC(001). [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A30.00003: Electronic transport properties of tungsten-decorated monolayer graphene Jamie Elias, Erik Henriksen The impact of tungsten adatoms on the electronic properties of monolayer graphene has been studied. Using a cryogenic probe capable of \textit{in situ} deposition of sub-monolayer coatings of most metals, we have evaporated tungsten onto the surface of graphene devices. For dilute coatings up to a 2.5\% coverage, the adatoms are found to donate electrons to the graphene, becoming charged impurities that reduce the carrier mobility. In addition, multiple lines of evidence point to the adatoms being isolated, point-like charge impurities, rather than clusters. Analysis of the conductivity at zero magnetic field, as well as the ratio of transport to quantum scattering times, suggests the adatoms are located approximately 1 nm above the surface. Surprisingly, this is about five times higher than predicted by density functional theory. Furthermore, we find a large discrepancy between the expected density of adatoms based on geometric changes in the evaporation source, when compared with the induced change in electron density due to charge doping. We hypothesize that both this discrepancy in evaporation densities, and the 1 nm separation, are a consequence of a remnant layer of PMMA residues from device fabrication. [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A30.00004: Transport properties of contaminated metal-graphene interfaces Bernhard Kretz, Christian S. Pedersen, Daniele Stradi, Mads Brandbyge, Aran Garcia-Lekue Interfaces between 2D nanostructures and bulk materials play an important role for a wide range of nanotechnology applications. Recently, graphene-metal contacts have been extensively studied and built into devices. In the process of fabricating such graphene-metal devices, contamination of the contact, and thus, doping of the graphene, may occur. Theoretical and experimental studies have shown, that controlled edge doping can significantly change the electronic structure of graphene.[1] Nevertheless, when occurring in an uncontrolled manner, edge-contamination has the potential of hugely modifying the electronic properties of graphene-metal interfaces in unforeseen ways. In our work, we carry our first-principles transport calculations to systematically investigate the influence of different edge-contaminations on the electronic and transport properties of graphene-metal contacts. Our studies shed light on the impact of the contaminants, as well as of the metal and of the contact conformation, on the conductance properties of such interfaces. \newline [1] P. Wagner et al., J. Phys. Chem. C 117, 26790 (2013); J. Cai et al, Nat. Nano 9, 896 (2014). [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:24AM |
A30.00005: Manipulation of Dirac cones in metal-intercalated epitaxial graphene Cai-Zhuang Wang, Minsung Kim, Michael Tringides, Kai-Ming Ho Graphene is one of the most attractive materials from both fundamental and practical points of view due to its characteristic Dirac cones. The electronic property of graphene can be modified through the interaction with substrate or another graphene layer as illustrated in few-layer epitaxial graphene. Recently, metal intercalation became an effective method to manipulate the electronic structure of graphene by modifying the coupling between the constituent layers. In this work, we show that the Dirac cones of epitaxial graphene can be manipulated by intercalating rare-earth metals. We demonstrate that rare-earth metal intercalated epitaxial graphene has tunable band structures and the energy levels of Dirac cones as well as the linear or quadratic band dispersion can be controlled depending on the location of the intercalation layer and density. Our results could be important for applications and characterizations of the intercalated epitaxial graphene. [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A30.00006: Interactions of Metal Nanoparticles through Graphene Li-Wei Huang, Chia-Seng Chang We employed ultra-high vacuum electron microscopy to investigate the interactions of metal nanoparticles through the graphene membrane. We observe that both aligning and repelling behaviors between the particles on the two sides of the graphene can happen, depending on the specific combination of Ag/Graphene/Ag, Cu/Graphene/Cu, or Au/Graphene/Au. Our findings reveal several potential mechanisms governing the interactions between the nanoparticles on and through a graphene. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A30.00007: Purely substitutional nitrogen on graphene/Pt(111) unveiled by STM and first principles calculations Jose M. Gomez-Rodriguez, Ana Martin-Recio, Carlos Romero-Muniz, Pablo Pou, Ruben Perez Nitrogen doping of graphene can be an efficient way of tuning its pristine electronic properties. Several techniques have been used to introduce nitrogen atoms on graphene layers. The main problem in most of them is the formation of a variety of C-N species that produce different electronic and structural changes on the 2D layer. Here we report on a method to obtain purely substitutional nitrogen on graphene on Pt(111) surfaces. A detailed experimental study performed in situ, under ultra-high vacuum conditions with scanning tunneling microscopy, low energy electron diffraction and Auger electron spectroscopy of the different steps on the preparation of the sample, has allowed us to gain insight into the optimal parameters for this growth method, that combines ion bombardment and annealing. This experimental work is complemented by first-principles calculations that provide the variation of the projected density of states due to both the metallic substrate and the nitrogen atoms. These calculations enlighten the experimental findings and prove that the species found are graphitic nitrogen. This easy and effective technique leads to the possibility of playing with the amount of dopants and the metallic substrate to obtain the desired doping of the graphene layer. [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A30.00008: Ab Initio Calculations of Nitrogen Functionalization of Graphene Olivier Malenfant-Thuot, Germain Robert-Bigras, Luc Stafford, Michel C\^{o}t\'{e} Our collaboration between theorists and experimentalists aims to achieve nitrogen functionalization of graphene with the late-afterglow regime of a microwave plasma. We hope this technique will give us a better control on the functionalization due to the small density of interacting atoms in the late-afterglow and a drastic diminution of induced defects compared to standard plasma functionalization techniques. With the software package ABINIT, we carried out first-principles calculations of different nitrogen atoms configurations in a graphene sheet. We obtained their formation energies to study whether they are realistic. We found that vacancies in the graphene sheet facilitate the incorporation of nitrogen atoms and, in particular, that the substitutional doping has the lowest formation energy. We also studied the energetic of nitrogen atoms adsorbed above the carbon plane and the interactions between those atoms. Using the Nudged Elastic Band method (NEB), we were able to calculate energy barriers for the diffusion and the in-plane absorption of these atoms. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A30.00009: Study the motion of domain wall in bilayer and trilayer graphene Lili Jiang, Zhiwen Shi, Sheng Wang, Feng Wang Layer-stacking domain walls in graphene strongly alters its electronic properties and gives rise to fascinating new physics. In bilayer graphene, domain walls between AB- and BA-stacking feature quantum valley Hall edge states, which promised novel approach to control valley degree for valleytronic devices; in trilayer graphene, they are connections of in-plane heterojunctions consisting of metallic ABA-stacking and semiconducting ABC-stacking. Domain walls take the form of soliton and can move freely in crystal. Near-field infrared nanoscopy is a powerful tool for visualizing domain walls in bilayer and trilayer graphene. In this study, we use near-field nano-imaging technique to investigate the motion of domain walls in bilayer and trilayer graphene. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A30.00010: Critical behavior of curvature localization in graphene Mrityunjay Kothari, Moon-Hyun Cha, Kyung-Suk Kim A multilayer graphene, when compressed, elastically buckles to a triangular crinkle shape even at the early stage of post bifurcation, with its maximum local slope change within a few degrees. Our DFT calculation shows that the graphene crinkle localizes and focuses surface curvature up to more than 10$^{-1}$ nm$^{-1\, }$along a narrow ridge of approximately 1nm width, and nullifies it elsewhere. In contrast, Koiter analysis of multilayer buckling predicts a simple-mode supercritical bifurcation, and progressive weak curvature focusing up to at most 10$^{-3}$ -- 10$^{-2}$ nm$^{-1}$ in a width of tens of nm's. However, when we include flexo-electric effects explicitly in the classical model, we observe instantaneous localization of curvature, at the onset of bifurcation, down to 1 nm width with curvature focusing close to the DFT prediction. The localization produces curvatures up to three orders of magnitude higher than the maximum curvature of a single-layer graphene wrinkle with an equivalent amplitude. The computational and theoretical predictions are in good agreement with our experimental studies in which we also demonstrated aligning of charged molecules with crinkle surface charges of flexo-electric polarization. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A30.00011: Molecular dynamics study on friction of multigrain graphene Aditya Kavalur, Woo Kyun Kim In addition to its extraordinary mechanical, electronic, and chemical properties, graphene is also a promising material for solid lubrication, which can be used for both macroscopic and small-length scale devices such as MEMS/NEMS. Although a significant number of research efforts have been devoted to unveiling the physical origin of its tribological properties from both experimental and theoretical standpoints, there are still many phenomena which remain far from completely understood. Graphene synthesized by CVD (chemical vapor deposition) is featured with the multi-grain structure, which may have detrimental effects on its mechanical and tribological properties. However, the friction of polycrystalline graphene has rarely been studied. In this study, we investigate the tribological properties of polycrystalline graphene using molecular dynamics methodology. Multigrain structures are created using a novel method and tested against pristine substrates (P-M), these results are compared with pristine-pristine (P-P) interactions. The P-M models exhibit a lower and wider range of friction forces, which may be explained through their individual configurations and a novel orientation-dependent mechanism of friction. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A30.00012: Giant and Tunable Anisotropy of Nanoscale Friction in Graphene Rodrigo Capaz, Marcos Menezes, Clara Almeida, Marcelo De Cicco, Carlos Achete, Benjamin Fragneaud, Luiz Gustavo Can\c cado, Ricardo Paupitz, Douglas Galv\~ao, Rodrigo Prioli The nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction coefficient of graphene is highly dependent on the scanning direction: Under some conditions, the energy dissipated along the armchair direction can be 80\% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15\%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations. [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A30.00013: Experimental observation of ballistic nanofriction on graphene Brandon Blue, Michael Lodge, Chun Tang, William Hubbard, Ashlie Martini, Ben Dawson, Masa Ishigami Recent calculations [Guerra et al, Nature Materials, 9, 634 (2010)] have predicted that gold nanocrystals slide on graphite with two radically different friction coefficients depending on their speeds. At high sliding speeds in the range of 100?m/s, nanocrystals are expected to behave radically differently in what is known as the ballistic nanofriction regime. In this work, we present a direct measurement of ballistic nanofriction for gold nanocrystals on graphene. Nanocrystals are deposited onto an oscillating graphene-coated quartz crystal microbalance (QCM) in-situ under UHV and allowed to periodically ring down. After deposition, frictional parameters are measured as a function of oscillatory velocity to investigate the predicted velocity dependence of friction. Lubricity beyond even the predictions of ballistic nanofriction is observed at much lower surface velocities than expected, with drag coefficients approaching 8.65*10$^{\mathrm{-14}}$ kg/s. In comparison to the theoretically-predicted value of 2.0*10$^{\mathrm{-13}}$ kg/s, our results suggest a much lower interaction strength than proposed in contemporary models of nanoscopic sliding contacts even at relatively low speeds. [Preview Abstract] |
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