Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P37: Focus Session: Graphene Structure, Dopants, and Defects: Strain Engineering II |
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Sponsoring Units: DMP Chair: Michael Crommie, University of California, Berkeley Room: C146 |
Wednesday, March 23, 2011 8:00AM - 8:36AM |
P37.00001: Beller Lectureship Talk: Gauge fields in graphene Invited Speaker: Graphene is a unique material with many special features not found in other systems. Elastic strains, and also topological defects, act on the charge carriers in the same way as effective gauge fields. The emergence of these fields, their dependence on sample parameters, and their relevance to experiments will be reviewed. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P37.00002: Limits on electron quality in suspended graphene due to flexural phonons Eduardo V. Castro, H. Ochoa, M.I. Katsnelson, R.V. Gorbachev, D.C. Elias, K.S. Novoselov, A.K. Geim, F. Guinea The temperature dependence of the mobility in suspended graphene samples has been investigated. In clean samples, flexural phonons become the leading scattering mechanism at temperature $T > 10\,\,$K, and the resistivity increases quadratically with $T$. Flexural phonons limit the intrinsic mobility down to a few m$^2$/Vs at room $T$, a value that is routinely achievable for graphene on a substrate. Their effect can be eliminated by applying strain. Similar qualitative behavior, even though with important quantitative differences, has been found for suspended bilayer graphene. [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P37.00003: Topological defect clustering and plastic deformation mechanisms in functionalized graphene Ricardo Nunes, Joice Araujo, Helio Chacham We present ab initio results suggesting that strain plays a central role in the clustering of topological defects in strained and functionalized graphene models. We apply strain onto the topological-defect graphene networks from our previous work [1], and obtain topological-defect clustering patterns which are in excellent agreement with recent observations in samples of reduced graphene oxide [2]. In our models, the graphene layer, containing an initial concentration of isolated topological defects, is covered by hydrogen or hydroxyl groups. Our results also suggest a rich variety of plastic deformation mechanism in functionalized graphene systems. \\[4pt] [1] Joice da Silva-Araujo, H. Chacham, and R. W. Nunes, Phys. Rev. B 81, 193405 (2010).\\[0pt] [2] C. Gomez-Navarro et al., Nano Lett. 10, 1144 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P37.00004: Electronic states of graphene grain boundaries Andrej Mesaros, Stefanos Papanikolaou, C.F.J. Flipse, Darius Sadri, Jan Zaanen Recent scanning tunneling spectroscopy measurements on graphite grain boundaries have identified zero energy peaks in the local density of states. These features are tied to intriguing magnetic properties observed in such samples, but are not found in existing theoretical models. We therefore study amorphous grain boundaries in graphene, and find stable structures along the boundary, responsible for local density of states enhancements both at zero and finite energies. We also consider the low energy continuum theory of arrays of dislocations forming a grain boundary in graphene. It predicts the appearance of localized zero energy states, pending the atomic scale dislocation core structure. We discuss possible stable dislocation core structures that actually carry such states. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P37.00005: Spectromicroscopy measurements of surface morphology and band structure of exfoliated graphene Kevin Knox, Andrea Locatelli, Dean Cvetko, Tevfik Mentes, Miguel Nino, Shancai Wang, Mehmet Yilmaz, Philip Kim, Richard Osgood, Alberto Morgante Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter research. ~However, crystal deformations in these 2D systems are known to adversely affect conductivity and increase local chemical reactivity. Additionally, surface roughness in graphene complicates band-mapping and limits resolution in techniques such as angle resolved photoemission spectroscopy (ARPES), the theory of which was developed for atomically flat surfaces. Thus, an understanding of the surface morphology of graphene is essential to making high quality devices and important for interpreting ARPES results. In this talk, we will describe a non-invasive approach to examining the corrugation in exfoliated graphene using a combination of low energy electron microscopy (LEEM) and micro-spot low energy electron diffraction (LEED). We will also describe how such knowledge of surface roughness can be used in the analysis of ARPES data to improve resolution and extract useful information about the band-structure. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P37.00006: Snap-through instability of graphene on corrugated substrates Cesar Chialvo, Scott Scharfenberg, Nikhita Mansukhani, Richard Weaver, Nadya Mason We discuss atomic force microscopy measurements of the interplay between interfacial bonding energy and strain energy in few-layer-graphene (FLG) placed on micro-scale corrugated metallic substrates. For fixed corrugation amplitude and wavelength, the theoretical strain energy of conformed FLG scales with the third power of its thickness. We present evidence of a so-called ``snap-through instability,'' where the behavior of the FLG abruptly changes, as a function of thickness, from fully conformed, to completely detached. The large FLG thickness, and by implication strain energy, at the snap-through point implies that the FLG-substrate bonding is larger than expected for van der Waals forces. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P37.00007: A Quantitative Characterization of Thermally Excited Ripples in Graphene Donald Priour, Jr In the framework of an atomistic model, we calculate the amplitude and typical wavelength of undulations in graphene sheets with length scales similar to those encountered in experiment. As part of a quantitative treatment, bond bending and stiffness constants are fixed by appealing to phonon frequency dispersion curves measured experimentally and from \textit{ab initio} electronic structure calculations. Equilibrium thermodynamic quantities, such as mean square atomic deviations and the average length scale (i.e. the typical ``wavelength'') of graphene ripples, are calculated in the context of statistical mechanical Monte Carlo simulations. Thermally induced rippling is examined for suspended graphene, as well as graphene in the presence of a substrate, where the attractive coupling of atomic species to the substrate layer is modeled with a Lennard-Jones potential. The contribution of quenched substrate disorder to undulations in the graphene sheet relative to the component of graphene ripples due purely to thermal fluctuations is studied by examining graphene sheets bound to substrates with various levels of intrinsic positional disorder. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P37.00008: Wrinkling of graphene membranes supported by silica nanoparticles on substrates Mahito Yamamoto, William Cullen, Michael Fuhrer, Theodore Einstein The challenging endeavor of modulating the morphology of graphene via a patterned substrate to produce a controlled deformation has great potential importance for strain engineering the electronic properties of graphene. An essential step in this direction is to understand the response of graphene to substrate features of known geometry. Here we employ silica nanoparticles with a diameter of 10-100 nm to uniformly decorate SiO$_{2}$ and mica substrates before depositing graphene, to promote nanoscale modulation of graphene geometry. The morphology of graphene on this modified substrate is then characterized by atomic force spectroscopy. We find that graphene on the substrate is locally raised by the supporting nanoparticles, and wrinkling propagates radially from the protrusions to form a ridge network which links the protrusions. We discuss the dependence of the wrinkled morphology on nanoparticle diameter and graphene thickness in terms of graphene elasticity and adhesion energy. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P37.00009: Magnetoresistance of Metal-Shunted Graphene Devices Paul Campbell, Adam Friedman, F. Keith Perkins, Jeremy Robinson Graphene, a single atomic layer of hexagonally arranged carbon atoms, presents the optimal platform to study magnetoresistance (MR) effects because of its temperature-independent mobility and linear band structure with zero band gap. Extraordinary magnetoresistance (EMR) can be realized in metal-shunted graphene devices. Here, due to the different magnetic-field-dependent resistances of the metallic shunt, graphene, and shunt-graphene interface, current flows easily through the shunt in zero and low magnetic field, while in high magnetic field, more current flows around the shunt and is redistributed in the graphene. Devices made from chemical vapor deposition (CVD) graphene grown on copper and transferred to a SiO$_{2}$/Si substrate with Ti/Au shunts display gate-tunable longitudinal MR of $\sim $600{\%} at 12 T and also show promise for use as Hall sensors. Graphene magnetoresistance devices have many possible applications including magnetic field sensors and magnetic read-heads. In contrast with the many proposed electronic uses for graphene, which necessitate the creation of a band-gap, graphene magnetoresistance devices that exploit LMR or EMR provide a use for as-grown or deposited graphene. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P37.00010: A Graphene-Based Biosensor Amal Kasry, Ali Afzali, George Tulevski, Bernhard Menges, Satoshi Oida, Matthew Copel, Libor Vyklicky Graphene, a single layer of carbon atoms, has attracted significant interest in several applications including biosensors. In this work graphene was grown by the CVD method. Optical parameters of graphene such as refractive index and extinction coefficient were measure by a mix of techniques including ellipsometer, XPS, Raman Spectroscopy, SPR and MEIS. Determining the optical properties of graphene allowed for study of its ability to sense biomolecular interactions. We also examined graphene modification by electrostatic interaction utilizing a molecule synthesized by IBM Research. Successful modification was proven by XPS, Raman Spectroscopy, and SPR. Studies of the chemical modification, along measurement of electrical and optical properties of graphene are components of our work to develop highly sensitive graphene-based sensors. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P37.00011: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P37.00012: Graphene-Silicon Schottky Diodes Chun Chung Chen, Mehmet Aykol, Chia-Chi Chang, A.F.J. Levi, Stephen B. Cronin By depositing mechanically exfoliated graphene on top of silicon substrates, the graphene-silicon Schottky barriers are observed. The resulting current-voltage characteristics exhibit rectifying diode behavior with a barrier energy of 0.41 eV on n-type silicon and 0.45 eV on p-type silicon at room temperature. The ideality factor is also evaluated for bilayer, three layer, and multiple layer graphene-silicon Schottky diodes at various temperatures. These results indicate that the number of graphene layers and the ambient temperature are major influences for the ideality factor of graphene-silicon Schottky diodes. In this work, photocurrents are observed under 532 nm laser illumination. The transparency of the thin graphene layer allows the underlying silicon substrate to absorb the laser light and generate a photocurrent. The full current-voltage characteristics under illumination are also reported. Spatially resolved photocurrent measurements also reveal the importance of inhomogeneity and series resistance in these devices. [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P37.00013: Conductance-Based Temperature Programmed Desorption with Single Defect Resolution Deng Pan, Patrick C. Sims, Brad L. Corso, Philip G. Collins The controlled functionalization of nanotubes and graphene requires methods of chemically attacking these inert surfaces and of removing unwanted oxidation damage. The appeal of reversible chemistries is rarely achieved: the degraded electrical properties of reduced graphene oxide compared to pristine graphene indicates residual damage that remains poorly understood. Using a high temperature, UHV apparatus to perform electrical measurements in situ, we investigate the thermal desorption of adducts that can restore conductivity in oxidized nanographites. The majority of our measurements are accomplished using SWCNTs, due to their enhanced sensitivity to even single point defects. Discrete conductance jumps accompanying the removal of different types of adducts provide a characterization method that directly distinguishes the relative electronic effects of phenolic, epoxide, and carboxylic defects. The electronic measurements complement more traditional, temperature programmed desorption from bulk material, which is insensitive to electronic disorder. [Preview Abstract] |
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