Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q36: Focus Session: Graphene Structure, Dopants, and Defects: Nanoparticles |
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Sponsoring Units: DMP Chair: Joshua Robinson, Penn State University Room: C142 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q36.00001: Manipulating graphene mobility and charge neutral point with ligand-bound nanoparticles as charge reservoir Deqi Wang, Xinfei Liu, Le He, Yadong Yin, Di Wu, Jing Shi In this work, we first demonstrate a significant enhancement in carrier mobility in SiO2-supported graphene decorated with a layer of ligand-bound nano-particles (NPs) such as iron oxide, titanium dioxide, or cadmium selenide acting as a charge reservoir. By transferring charges between graphene and the NP reservoir through the molecules, we show a remarkable reversible tunability in mobility (4,000 -- 19,000 cm2/Vs) in the same device, which unambiguously proves that the charged impurity scattering is the prevailing mechanism for graphene mobility. In addition, the charge neutral point can also be independently tuned over a wide gate voltage range. Finally, we study the thermopower of graphene sample with different mobility. By properly taking account of the high temperature effects, we obtain good agreement between the Boltzmann transport theory and our experimental data. [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q36.00002: Imaging grain boundaries in monolayer graphene by transmission electron microscopy Kwanpyo Kim, Zonghoon Lee, William Regan, C. Kisielowski, M. Crommie, A. Zettl Using transmission electron microscopy (TEM), we investigate the structure of grain boundaries in large-area monolayer polycrystalline graphene sheets at micron and atomic length scales. At micron scale, grain boundary mapping is performed by electron diffraction and dark field imaging techniques. The atomic scale imaging by an aberration-corrected ultra-high resolution TEM reveals an alternating pentagon-heptagon structure along the high-angle tilt grain boundary. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q36.00003: Electromagnetic interaction of graphene with nanoparticles: applications to nanoscale imaging spectroscopy and plasmonics L.M. Zhang, A.H. Castro Neto, Michael Fogler Interaction of graphene-covered substrate with a nearby nanoscale particle is studied theoretically. Graphene is shown to induce broadening and frequiency shifts of electromagnetic resonaces (cavity modes) localized near the particle. The effect is strongly enhanced for substrates that possess narrow surface polariton excitations. In turn, the coupling to polaritons modifies the spectrum of graphene plasmons. The theory is applied to model scanning near-field optical microscopy (SNOM) experiments where the role of nanoparticle is played by the sharp tip of the scanned probe. The origin of the extraordinary fine spatial resolution of SNOM is explained and proposals for detecting the novel modes by SNOM in the infrared and THz domains are outlined. Also discussed are other applications, including infrared and Raman scattering from graphene covered by a layer of colloidal nanoparticles. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:27PM |
Q36.00004: Interlayer Physics in Few Layer Graphenes Invited Speaker: Few layer graphenes (FLG's) represent a family of materials with physical properties distinct from those of single layer graphene and bulk graphite. Their electronic behavior is determined by the nature of electronic motion between layers and by the interactions of electrons in different layers. This talk reviews our experimental and theoretical work studying aspects of nanoparticle growth on FLG's that are determined by this interlayer physics. We observe and analyze: (1) a systematic film thickness dependence of the surface potential for FLG's deposited on SiO$_{2}$ substrates, (2) a related thickness dependence of the sizes of gold nanoparticles that nucleate on the exposed surface of FLG's and (3) a shape instability for growing nanoparticles formed from low workfunction metals adsorbed on FLG's. Finally we discuss some novel aspects of the interlayer electronic motion that are controlled by the rotational registry of neighboring layers. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q36.00005: Energetics and Electronic Structure of Transition Metal Adatoms and Clusters on Graphene Christopher Porter, David Stroud Using density functional theory (DFT), we calculate both the atomic arrangement and electronic structure of transition metal (TM) adatoms, and clusters of adatoms, on graphene. We use a periodic arrangement of unit cells which typically include about 64 C atoms. For Fe on graphene, we have found that the stable position of the adatom is above the center of a hexagon of C and that most of the relaxation in the graphene occurs in the six C atoms closest to the adatom. We use DFT to map out a potential energy surface for Fe adatoms on graphene at any point in the unit cell, allowing an estimate of the energy barrier for an adatom to hop from one energy minimum to another. We also calculate the lowest energy configurations of pairs and larger clusters of TM adatoms on graphene. Finally, we have calculated the electronic structure and density of states associated with the adatoms and clusters on graphene, and have extended these calculations to spin- dependent properties, using a spin density functional approach. These results should be relevant to electronic and spin transport properties of graphene, both of which are expected to be strongly influenced by TM adatom impurities. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q36.00006: Doping efficiencies and physisorption of small molecules on graphene Alexander Samuels, David Carey Ab initio calculations have been employed to study the doping efficiencies of NO$_{2}$, NO and NH$_{3}$ on graphene. We have used both the local density approximation (LDA) and the generalised gradient approximation (GGA) to obtain the molecular binding energies and have employed the Hirshfield charge transfer method to calculate the charge transfer. Spin polarised calculations were employed for the open shell molecules (NO and NO$_{2})$ and we explored the effects of different adsorption sites and orientations. It was found that for all orientations of the molecule and using both LDA and GGA functionals that the adsorption of NO$_{2}$ results in p type doping of graphene with 0.06 e transferred to the molecule. For NO, LDA calculations show a p type behaviour with 0.03 e transferred per molecule but both n and p type doping of 0.003 -- 0.004 e/molecules is calculated using a GGA functional. Finally for NH$_{3}$ both donor and acceptor behaviour (0.03 -- 0.05 e/molecule) is calculated. In all cases the origin of the doping is related to the relative position of the HOMO and LUMO molecular orbitals with respect to the graphene Dirac point and low energy density of states. The effect of molecular adsorption on electron scattering is also discussed. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q36.00007: Surface Functionalization of Graphene Field Effect Transistors with Polyhistidine-Tagged Proteins Ye Lu, Joseph Mitala, Jong-Hsien Lim, Mitchell Lerner, Zhengtang Luo, Nicholas Kybert, Brett Goldsmith, Bohdana Discher, A.T. Charlie Johnson We have developed a facile and reliable method to covalently functionalize the surface of graphene field effect transistors (FETs) with polyhistidine-tagged proteins We demonstrated success of chemical functionalization by both atomic force microscopy (AFM) and Raman spectroscopy. Additionally, we characterized the electronic properties of graphene FETs at successive functionalization stages. The specificity enabled by such functionalization, along with the two dimensional nature and intrinsic high sensitivity of graphene, facilitates the emergence of graphene as a promising candidate in surface biochemistry research as well as graphene-based biosensor applications. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q36.00008: First principles simulations of molecules and nanostructures subjected to ion irradiation Kalman Varga, Sergiy Bubin, Bin Wang, Sokrates Pantelides In the framework of real-time real-space time-dependent density functional theory complemented with classical molecular dynamics for ions, we have studied the behavior of small molecules and nanostructure fragments, such as graphene sheets, irradiated by charged energetic particles. In particular, we have investigated the importance of electronic excitations and examined the regime when bond breaking (or defect formation) occurs. Based on the microscopic description of these processes, several quantities that are of interest for ion beam physics have been determined, such as the amount of energy transferred to the target system and the distribution of this energy between electronic excitations and vibrational motion. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q36.00009: Point and Line Defect-mediated Binding of Metal Nanoparticles to Graphene Ioanna Fampiou, Ashwin Ramasubramaniam The synthesis of well dispersed, size-controlled metal nanoclusters on carbon supports is highly desirable since such clusters have been shown to possess enhanced catalytic activity and selectivity in a variety of chemical reactions. However, metal clusters interact rather weakly with defect-free carbon supports and can coarsen over time leading to loss of surface area and thence catalytic activity. Defects in carbon supports play an important role in enhancing metal-carbon bonding, thereby reducing the propensity for cluster coalescence. Using a combination of density functional theory and empirical potential simulations, we examine the interaction of metal Pt clusters with point (vacancies, holes) and line defects (dislocations, grain boundaries) in graphene. We compare and contrast the binding energies and diffusivities of clusters bound at defects and on pristine graphene. Our results suggest possible avenues for controlling the dispersion of Pt catalyst clusters on carbon supports via defect engineering. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q36.00010: Molecular Mechanics on Graphene Surface and its Detection Kabeer Jasuja, Nihar Mohanty, Vikas Berry In this talk, we demonstrate that the light-induced reversible mechanical motion of an azo-molecule-tethered on graphene can be sensitively detected electronically by motion-induced molecular-gating of graphene (without external gate). The \textit{in-situ} mechanical actuation of the azo-molecule is shown to redistribute the fermionic density \textit{via} due to the change in the proximity of electron-rich benzene moiety of the azo molecule. The results demonstrate that the ultra-sensitive platform offered by graphene makes it possible to electrically detect molecular-scale mechanics. We envision that this research will enable development of next-generation graphene based actuating systems with applications including FETs, optoelectronic-switches and nano-pistons. [Preview Abstract] |
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