Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L36: Focus Session: Graphene Structure, Dopants and Defects: Adsorbates |
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Sponsoring Units: DMP Chair: Dmitry Abanin, Princeton University Room: C142 |
Tuesday, March 22, 2011 2:30PM - 2:42PM |
L36.00001: First-principles calculations of gated adatoms on graphene Kevin T. Chan, Hoonkyung Lee, Marvin L. Cohen The two-dimensional surface of graphene is well-suited for adsorption of adatoms or molecules. The application of a gate voltage can be used to precisely control the electron concentration of the adsorbate-graphene system. Such control over electronic properties of adsorbates on graphene might have useful applications in areas such as catalysis and hydrogen storage. In this work, the gating of a variety of adatoms adsorbed on graphene is studied using first-principles calculations. We compute the projected density of states, local electrostatic potential, and charge density of the adatom-graphene system as a function of gate voltage. We demonstrate that adatoms on graphene can be ionized by gating, and that the ionization causes a sharp change in the electrostatic potential. Additional interesting features of our results are also discussed. [Preview Abstract] |
Tuesday, March 22, 2011 2:42PM - 2:54PM |
L36.00002: High-resolution measurement of SiO2 surface potential using scanning Kelvin-probe microscopy William Cullen, Kristen Burson, Mahito Yamamoto, Michael Fuhrer It is now widely recognized that the dominant contribution to disorder in SiO$_2$-supported graphene is due to scattering from charged impurities. These charged impurities give rise to a conductivity which is linear in carrier density, and create electron-hole puddles in graphene. The screened potential variation produced in graphene has been imaged using scanning tunneling microscopy/spectroscopy (STM/STS) by spatially mapping the variation in the Dirac point, revealing a length scale of ~20 nm for the charge puddles. However, there is a substantial gap in resolution between the STM measurements and previous measurements with much greater potential sensitivity but limited spatial resolution. Here we attempt to bridge this gap using scanning Kelvin-probe microscopy (SKPM) of SiO$_2$ in ultrahigh vacuum. Our measurement takes advantage of the high spatial resolution allowed by UHV non-contact AFM while maintaining UHV control of the sample environment.\\[4pt] [1] Y. Zhang et al., Nature Physics 5, 722 (2009)\\[0pt] [2] J. Martin et al., Nature Physics 4, 144 (2008) [Preview Abstract] |
Tuesday, March 22, 2011 2:54PM - 3:30PM |
L36.00003: Revealing the dominant scatterer in Graphene on SiO$_{2}$ Invited Speaker: Freely suspended graphene sheets display high-field effect mobility, reaching 2$\times $10$^{5}$ cm$^{2}$ /V s. Yet, suspended graphene sheets are fragile and impractical for most experiments and applications. Graphene sheets on SiO$_{2}$ are easier to handle but possess low-carrier mobilities, which can even vary by an order of magnitude from sample to sample. Poor and unpredictable transport properties reduce the utility of SiO$_{2}$-bound graphene sheets for both fundamental and applied sciences. Therefore, understanding the impact of substrates is crucial for graphene science and technology. We [1] have measured the impact of atomic hydrogen adsorption on the electronic transport properties of graphene sheets as a function of hydrogen coverage and initial, pre-hydrogenation field-effect mobility. The saturation coverages of atomic hydrogen for different devices are found to be proportional to their initial mobility, indicating that the number of native scatterers is proportional to the saturation coverage of hydrogen. By extrapolating this proportionality, we show that the field-effect mobility can reach 1.5$\times $10$^{4}$ cm$^{2}$ /V s in the absence of the hydrogen-adsorbing sites. The affinity to atomic hydrogen is the signature of the most dominant type of native scatterers in graphene-based field-effect transistors on SiO$_{2}$. The dominant scatterer is identified by comparing the reactivity of charge puddles, ripples and resonant scatterers to atomic hydrogen. \\[4pt] [1] J. Katoch, J.H. Chen, R. Tsuchikawa, C. W. Smith, E.R. Mucciolo, and M. Ishigami, Uncovering the dominant scatter in graphene sheets on SiO2, Physical review B. Rapid Communications, 82, 081417 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 3:30PM - 3:42PM |
L36.00004: Magnetic field effects on the local electronic structure near a single impurity in Graphene Ling Yang, Jian-Xin Zhu, Shan-Wen Tsai Impurities in graphene can have a significant effect on the local electronic structure of graphene when the Fermi level is near the Dirac point. We study the problem of an isolated impurity in a single layer graphene in the presence of a perpendicular magnetic field. We use a linearization approximation for the energy dispersion and employ a T-matrix formalism to calculate the Green's function. We investigate the effect of an external magnetic field on the Friedel oscillations and impurity-induced resonant states. Different types of impurities, such as vacancies, substitutional impurities, and adatoms, are also considered. [Preview Abstract] |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L36.00005: Tunable magnetoresistance behavior in suspended graphitic multilayers through ion implantation Carlos Diaz-Pinto, Xuemei Wang, Sungbae Lee, Viktor Hadjiev, Debtanu De, Wei-Kan Chu, Haibing Peng A linear positive magnetoresistance (MR) is often observed in graphitic multilayers, yet its origin remains inconclusive. Recently, a non-Markovian transport theory predicts a strong positive MR in two dimensional systems under the influence of both short- and long-range disorders, while a negative MR is expected with only one type of disorder. Here, we address the role of disorders on the MR behavior of suspended graphitic multilayers through ion implantation. Boron implantation is found to drastically change the MR behavior: the linear positive MR transforms into a negative MR after the introduction of short-range disorders (boron), in consistence with the non-Markovian theory. This suggests that the origin of the unexplained linear positive MR in graphitic structures is the non-Markovian transport under the interplay between long-range disorders (charged surface adsorbents) and short-range disorders (defects inside the lattice). After ion implantation, short-range disorders dominate, leading to a distinct negative MR behavior. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L36.00006: Raman spectroscopic study of chemically-doped few layer graphenes PingHeng Tan, WeiJie Zhao, Jun Zhang, Jian Liu Graphene, the latest carbon allotrope discovered at 2004, has attracted intensively scientific interest owing to its distinctive properties. Chemical doping is expected to substantially increase the density of free charge carriers by charge transfer and to modify the Fermi level of doped materials. Here, we investigated charge transfer and optical phonon mixing in few layer graphenes in detail by utilizing sulfuric acid as an electron-acceptor dopant. Sulfuric acid molecules are found to be only physically adsorbed on the surface layers of graphenes and no intercalation happens. The top and bottom layers of bilayer graphenes can be intentionally doped differently by concentrated sulfuric acid. The difference of hole doping between the top and bottom layers results in phonon mixing of symmetric and antisymmetric modes in bilayer graphenes. The Raman frequency evolution with the doping level qualitatively agrees with recent ab initio theoretical calculations. Sulfuric acid molecules can be expected as a stable electron-acceptor dopant for graphenes to study the physical properties of few layer graphenes at different doping levels. [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L36.00007: The doping mechanism in graphene Razvan A. Nistor, Dennis M. Newns, Glenn J. Martyna Doping graphene by adsorbing chemical species on its surface is one way to control the carrier concentration of this novel material. Using large-scale {\it ab initio} simulations and electronic structure calculations, we show the carbon layer acts as a metal catalyst facilitating the disproportionation reaction of adsorbed chemical species on its surface. This reaction leads to the formation of charge transfer complexes which thereby dope the graphene. We also investigate the charge transfer in graphene-silicon and defected graphene-silicon-oxide interfaces. Our microscopic understanding of the doping mechanism in graphene, which brings to light the catalytic power of the material, is important in the development of carbon-based electronics. [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:30PM |
L36.00008: Understanding Graphene Coatings: Characterization of Solvent Exfoliated Few-Layer Graphene by Raman Scattering Jorge Camacho, Lester Lampert, Willson Arifin, Robby Flaig, Timothy Rue, Tyler Krisko, James Hamilton Graphene has unique properties like its ballistic transport at room temperature combined with chemical and mechanical stability and these properties can be extended to few-layer of graphene. Potential large-area applications that include transparent conductive coatings and fuel cell electrodes require dispersing graphene in a fluid phase. Graphene nano-platelets can be synthesized by dispersion and exfoliation of graphite in organic solvents such N-methyl-pyrrolidine (NMP) and cyclohexylpyrrolidone (CHP). However, liquid-phase exfoliation produces graphene with defects that can disrupt the electronic properties. One of the remaining questions is whether the defects created during synthesis can be minimized. We report a Raman spectroscopic study showing that defects in few-layer graphene produced by liquid-phase exfoliation of graphite can be controlled by the type or mixture of solvents used. [Preview Abstract] |
Tuesday, March 22, 2011 4:30PM - 4:42PM |
L36.00009: First Principles Study of Interactions between Dopant Atoms in Graphene Nabil Al-Aqtash, Igor Vasiliev We study the interactions between the boron (B) and nitrogen (N) dopant atoms in graphene. Our calculations are carried out using density functional theory combined with the generalized gradient approximation for the exchange-correlation functional. The total energies, equilibrium geometries, electronic charge distributions, and densities of states of doped graphene sheets are examined in cases of B-B, N-N, and B-N co-doped graphene. The interaction energy between the two dopant atoms is found to be inversely proportional to the square of the separation distance. We find the B-B and N-N interactions to be repulsive and the B-N interaction to be attractive. The changes in the density of states observed in B- and N-doped graphene are explained in terms of electronic charge transfer. [Preview Abstract] |
Tuesday, March 22, 2011 4:42PM - 4:54PM |
L36.00010: Bonding and charge transfer induced by metal adatom adsorption on graphene Xiaojie Liu, C.Z. Wang, M. Hupalo, Y.X. Yao, M.C. Tringides, Wen-Cai Lu, K.M. Ho Structures and adsorption energies of alkali, simple, transition as well as rare earth metal adatoms on graphene were studied systematically by first-principles calculations. Bonding character and charge transfer between the metal adatoms and the graphene were also analyzed using the quasi-atomic minimal basis set orbitals (QUAMBOs) approach. We showed that the interaction between the alkali metal adatoms and graphene can be characterized as ionic with minimal effects on the lattice and electronic states of the graphene layer. On the other hand, transition metal adsorption exhibits strong covalent bonding and induces large distortion in the lattice and electronic states of the graphene. For trivalent simple metal adatom adsorption, mixed covalent and ionic bonding is observed. Interaction of rare earth adatoms with graphene can be either ionic or covalent depending on the specific elements. Charge redistributions upon the metal adsorptions also induce significant electric dipole moments and changes in the magnetic moments of the adatoms. These results are confirmed by STM studies of the nucleated island density in epitaxial growth experiments. [Preview Abstract] |
Tuesday, March 22, 2011 4:54PM - 5:06PM |
L36.00011: Transport properties of metalo-organic functionalized graphene Stefan C. Badescu, Victor M. Bermudez, Thomas L. Reinecke Transition metal atoms can act as strong covalent anchors for organic molecules on graphene. The hybridization between the metallic d orbitals and the p orbitals of graphene provides a doping method without breaking C-C bonds. Using first-principle calculations for a range of adsorbed transition metals we identify the induced impurity levels and we reveal a dependence of the spin states on adsorbate coverage. We construct sets of maximally localized Wannier functions that interpolate accurately the calculated bandstructures. These sets are used then to describe the electronic transport from the dilute regime to finite coverages. [Preview Abstract] |
Tuesday, March 22, 2011 5:06PM - 5:18PM |
L36.00012: The electronic structure and chemical bonding of graphene doped with Group IA and Group VIIA elements: A density functional theory study Yiming Mi, Shuichi Iwata The ground state geometry and the electronic structure of graphene doped with group IA and VIIA elements were calculated with the first principles plane wave pseudopotential approaches within the density functional theory formalism in this paper. In terms of the generalized gradient approximation(GGA), GW approximation and optimizing atomic positions, a reliable geometry of the structure was acquired. The calculated formation energies for different configurations under ambient temperature implied that a new kind of material will produce. The results acquired here allow one to suggest new material with semiconductor or semimetallic behavior by adjusting the relative concentration of the doped atoms carefully. [Preview Abstract] |
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