Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z14: Graphene: Adsorbates and Defects |
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Sponsoring Units: DMP DCMP Chair: Bobby Sumpter, Oak Ridge National Laboratory Room: B113 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z14.00001: Electronic and transport properties of heme-b adsorbed on graphene nanoribbons Eduardo Cruz-Silva, Marcia Bojorquez-Avitia, Rodolfo Cruz-Silva, Florentino Lopez-Urias, Vincent Meunier, Mauricio Terrones, Bobby G. Sumpter Heme-B is the prosthetic group of several hemoproteins, such as several peroxidases and hemoglobin. It contains an Iron atom that can be oxidized or reduced depending on its environment. Changes in Iron oxidation state enable diverse biological functions like oxygen transport and electron transfer. In this work, we present a quantum density functional study on the adsorption of a heme-b group in graphene. The effects of heme-b adsorption on the graphene electronic structure will be shown. These changes have clear effects on the quantum transport properties of graphene, which coupled with the affinity of heme-b group to molecules like oxygen, carbon dioxide and carbon monoxide, could help to develop new graphene based amperometric biosensors. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z14.00002: Alkali and halogen adsorption on graphene using ab initio calculation ChengIng Chia, Vincent Crespi A seamless sp2 graphene sheet prevents the penetration of atoms through the sheet, yet allows the penetration of electrons. Thus, a suspended single sheet graphene forms a geometrical constraint by separating the surrounding vacuum into upper half and lower half spaces. Alkali and halogen atoms, each constrained to one of the spaces, are forced to interact electrostatically via charge transfer through the sheet. We have found that under this constraint, a K atom can break the Cl-Cl bond of a chlorine molecule and form a new class of inter-atomic interaction, with strong long-ranged Coulomb effects on the band-structure. This investigation has now been extended to other alkali atoms (Na, Rb) and halogens (Br, I) to determine the generality of these new physical effects. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z14.00003: Ab-initio study of hydrogen atom pairs adsorption on potassium doped graphene Jorge-Alejandro Tapia, Cesar Renan, Gabriel Canto, Ruben Medina-Esquivel, R. de Coss The effects of the interactions of hydrogen (H) atoms on graphene (G) with potassium (K) pre-adsorbed, were predicted by means of first-principles calculations. The results were obtained with the pseudopotentials method and the generalized gradient approximation for the exchange-correlation potential. The structural parameters, bonding, electronic structure and magnetic properties of two H atoms on potassium doped graphene (2H-K/G) system are calculated by molecular dynamics. We found an important charge transfer from the K atom towards the G surface when an H atom was adsorbed, producing a chemical bonding transition from sp$^{2}$ to sp$^{3}$ in the bonded carbon atom. The binding energy per H atom was greater in the 2H-K/G system than both H-K/G and a H atom on the single G systems (H/G). The present results suggest that the hydrogen adsorption on graphene layer could be modulated by the pre-adsorption of potassium. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z14.00004: Characterization and Control of the Barrier for Hydrogen Adsorption on Graphene Alejandro Suarez, Ljubisa Radovic, Jorge Sofo We study the chemisorption of atomic hydrogen on graphene. The barrier for chemisorption is about 0.21 eV. We explain the evolution of the partial density of states of the hydrogen and carbon atoms in graphene upon adsorption with a simple three-site Hubbard model. The barrier results from the competition between the pi-bonding between carbon atoms and the covalent bonding with hydrogen. With knowledge of the principles at play, we propose adjustments to the graphene plane which lower or eliminate this adsorption barrier. With a reduced barrier, formation of graphane can be facilitated, and applications for selective hydrogen desorption to create channels are discussed. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z14.00005: The Effect of Cluster Formation on Graphene Mobility Kathleen McCreary, Kyle Pi, Adrian Swartz, Wei Han, Wenzhong Bao, Jeanie Lau, Francisco Guinea, Mikhail Katsnelson, Shan-Wen Tsai, Roland Kawakami The transport properties of graphene are strongly influenced by the presence of impurities on the surface. Additionally, the structure of the impurities, whether in the form of clusters or isolated adatoms, has an effect on scattering. Using molecular beam epitaxy, small amounts of gold impurities are introduced to the graphene surface. When deposited at low temperatures, the resulting decrease in mobility and a shift in Dirac point is consistent with scattering from point-like charged impurities. To investigate the effect of the formation of clusters, the temperature is slowly raised to room temperature while transport properties are monitored. For a fixed amount of gold impurities, it is discovered that the formation of clusters significantly enhances the mobility and causes the Dirac point to shift back toward zero. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z14.00006: Local density of states and scanning tunneling currents in graphene Ling Yang, Nuno Peres, Shan-Wen Tsai Graphene consists of an atom-thick layer of carbon atoms arranged in a honeycomb lattice, and its low-energy electronic excitations are well described as massless Dirac fermions with spin half and an additional pseudospin degree of freedom. We study local properties of graphene with isolated impurities (diagonal and non-diagonal impurity potential) such as the local electronic spectra and real-space and k-space local density of state (LDOS) maps. Using a multimode description for an scanning tunneling microscope (STM) tip, we calculate STM currents and find that strong resonances in the LDOS at finite energies lead to the presence of steps in the STM current and suppression of the Fano factor. [Ref: N. M. R. Peres, L. Yang, and S.-W. Tsai, New J. Phys. 11, 095007, (2009)] [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z14.00007: Ab-initio study of NH3 and NH adsorption over graphene Cesar Cab, Felipe Cab, Alejandro Tapia Currently, solid state sensors for detecting chemicals are an intensive area of research and development. Solid state sensors have advantages over conventional systems such as decrease the size and cost, broadening the range of applications. In this work we study the possibility of using graphene for the detection of NH3 and NH, through structural and electronic changes induced in graphene by adsorption of both molecules. The results are obtained with the seudopotential LCAO and GGA approximation for the exchange correlation potential. Study reveals that nitrogen in the NH and NH3 molecules have affinity for the surface of graphene. Analysis of charge transfer is performed to analyze the adsorption process. The molecules have preferential sites of adsorption for NH3, which are the interstitial sites of the hexagonal lattice, the links between carbon atoms, and over the carbon atoms. In the case of NH (nitrene) these sites correspond to the spaces between links, and over carbon atoms. Also, adsorption of both molecules produces major distortions in the network of graphene, which are analyzed. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z14.00008: Physisorption of nucleobases on graphene: the role of van der Waals interactions Duy Le, Abdelkader Kara, Talat S. Rahman The physisorption of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) on graphene is studied within the generalized gradient approximation (GGA) of the density functional theory (DFT) with the inclusion of van der Waals interaction (vdW) based on the London dispersion equation. We find that the inclusion of the latter interaction increases the binding energy by about 0.5eV (from an almost zero value) and moves these nucleobases by about 0.5{\AA} toward the graphene, as compared to the results obtained with regular DFT-GGA. The binding energies of nucleobases on graphene are found to be in the following order: G$>$A$>$T$>$C$>$U, with a dispersion of about 200meV. Details of the dynamics (diffusion barriers) and adsorption characteristics of these nucleobases on graphene will be presented as well as the description of their electronic structure and nature of the bonding with the substrate. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z14.00009: Absence of a supercritical regime induced by short-range impurity scattering in gapped graphene Stepan Grinek, Zhou Lie, Jie Chen, Qinwei Shi, Frank Marsiglio We show that the changes in the electronic density of states (DOS) in graphene induced by impurity scattering with short-range potentials are completely different from those caused by the long-range Coulomb potential. The spectral weight of the state that eventually disappears into the valence band (as the strength of scattering increases) does not transform into a resonance state. Therefore no unusual screening effects related to a redistribution of the density of states in the valence band are observed. The states induced by the short-range impurities in graphene, therefore, have distinctively different properties compared with the long-range potential case. These properties, in fact, closely resemble the case of a short-range single impurity in other bipartite lattices, such as the square, body centered cubic, and simple cubic lattices. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z14.00010: Fullerenes, Zero-modes, and Self-adjoint Extensions Abhishek Roy, Michael Stone The continuum Dirac hamiltonian provides a good account of the low-energy eigenstates on an infinite sheet of graphene. It is also known that that geoemetric defects, such as the pentagons that occur in fullerenes, may be modelled by a spin connection and a non-abelian gauge field. We show here that to understand the bound states localized in the vicinity of a pair of pentagons one must, in addition to the gauge flux, consider the effect of the short-range lattice disruption near the defect. Although the defect appears as a point object to low wavelength excitations, there is additional information contained in non-trivial boundary conditions that need to be imposed at this point to ensure self-adjointness of the hamiltonian. We demonstrate that by adjusting this boundary conditions one may analytically match the results of a numerical tight-binding calculation. To appear in Journal of Physics A. Archive number: arXiv:0909.1569v1 [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z14.00011: Patterning Effects on electronic Properties of Hydrogenated Graphene Superlattices M. Yang, Y. P. Feng, T. Venkatesan, A. Ariando, C. Zhang Recently, it was found that the absorption of hydrogen atoms on graphene can modify the electronic properties greatly. This finding not only opens another possibility for tuning the electronic properties of graphene, but also allows us to pattern hydrogenated graphene to obtain the desired electronic properties. Here, we report results of density-functional based tight-binding calculations of patterning effects such as pattern edge, pattern shape (triangular and hexagonal shape) and type (zigzag and armchair), and lattice pattern (triangle and square) and size on electronic properties of hydrogenated graphene superlattices. It is found that electronic properties of hydrogenated graphene superlattices are sensitive to the pattern edge. Superlattices with zigzag edge, have very small bandgaps or are metallic. Supperlattices with armchair edge, exhibit much larger bandgaps whose magnitude is dependant on the pattern shape, lattice, and pattern size. In addition, electronic properties of a quantum dot, formed by removing a lattice from the two-dimensional hydrogenated graphene superlattices, will also be discussed. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z14.00012: Factors Contributing to Size Selection of Metal Nanoparticles on Graphene Luke Somers, Eugene Mele, Zhengtang Luo, A.T. Charlie Johnson We examine layer number dependence in the size of metal nanoparticles grown on single and multilayer graphene. Graphene offers a smooth inert substrate for nanoparticles, in particular for particles grown in situ. Upon annealing, the particles forming on thin layers are smaller. A theory based on balance between self-repulsive dipole interaction and surface tension is presented. We test this theory by examining size distributions for various metals. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z14.00013: Resonant Impurity band induced by point defects in graphene Chung-Yu Mou, Bor-Luen Huang In this talk, we shall present our theory of point defects on graphene. In particular, we shall pointed out that point defects on graphene are strongly correlated and can not be treated as independent scatters. For large on-site defect potential and finite quasi-particle lifetime, we show that defects induce an impurity band with density of state characterized by the Wigner semi-circle law. By including long-range Coulomb interaction, we show that depending on, quasi-particle lifetime and defect density, the impurity band may support ferromagnetism. Furthermore, the impurity band can enhance the conductivity of graphene to the order of 4e$^2$/h, in consistent with experimental observations. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z14.00014: Doping a graphene sheet with impurities Chih-Kai Yang It has been predicted theoretically and achieved experimentally that a graphene sheet can bond strongly with hydrogen atoms. The resulted hydrocarbon or graphane is a semiconductor with a large band gap around 3.5 eV. In the paper I discuss the density functional calculation that shows how the pristine graphene is attached to lithium, creating instead a metal. In the case of graphane, the calculation also predicts that defects and doping with transition-metal impurities can greatly enhance the conduction and generate high magnetic moments. These properties offer promising application of doped graphane as a nanoelectronic device. [Preview Abstract] |
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