Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session X25: Theory and Simulation of Carbon Nanotubes |
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Sponsoring Units: DCOMP Chair: Jeffrey C. Grossman, LLNL Room: LACC 501A |
Friday, March 25, 2005 8:00AM - 8:12AM |
X25.00001: Optical and Electromechanical Properties of Graphene and Carbon Nanotubes via a Two-Field Elastic Description. Cristiano Nisoli, Vincent Crespi A two-fields continuum model for graphene and carbon nanotubes describes a wealth of phenomena inaccessible to the na\"ive continuum approach, such as optical bands in graphite and nanotubes, the hexagonal Brillouin zone in graphene, phonons spectra beyond the long-wavelength regimen and Raman active optical modes; by taking into account all the degrees of freedom of the honeycomb lattice, it is best suited for dealing with electromechanical effects, such as doping induced deformations, or strain induced band gap opening. [Preview Abstract] |
Friday, March 25, 2005 8:12AM - 8:24AM |
X25.00002: Electron excitations in doped semiconducting carbon nanotubes Eugene Pivovarov, Michael Fogler We compute the dispersion of electron excitations of a doped semiconducting carbon nanotube based on a model of a one- dimensional electron gas with Coulomb interaction and two-fold orbital degeneracy. The SU(4) symmetry of the model leads to a rich spectrum with multiple isospin modes in addition to the usual plasmons and spinwaves. A recently developed approximate mapping of the problem in hand onto integrable models enables us to do computation in the most interesting strongly correlated regime of low doping, where velocities of the isospin and plasmon modes become very different. We discuss anomalous transport and tunneling properties that may be observable in this regime. [Preview Abstract] |
Friday, March 25, 2005 8:24AM - 8:36AM |
X25.00003: Effect Of Electron Correlation On Shielding Pair Intercation Potential In Carbon Nanotubes John Adams, Yuriy Malozovsky We study the effect of short-range and exchange electron correlation in the carbon nanotubes (CNTs). We model the carbon nanotube as a tubule with electrons confined to the surface of the tubule by an attractive delta-function potential. We derived the pair interaction potential between two charges in the presence of the tubule in terms of the generalized random phase approximation (GRPA) incorporating short-range and exchange correlation. The Hubbard like local field factor for the nanotube is derived in terms of the variation procedure of the exchange part of the self-energy for the nanotube with respect to the electron's distribution function. The pair interaction potential is derived for an arbitrary position of two charges with respect to the tubule. We discuss the application of the pair interaction potential for evaluation of the energies of activation for the diffusion of the atomic particles like Li and H in carbon nanotubes. We also discuss application of the pair interaction potential for molecular dynamics simulation of carbon nanotubes. [Preview Abstract] |
Friday, March 25, 2005 8:36AM - 8:48AM |
X25.00004: Effect Of Electron Correlation In Carbon Nanotubes Russell Selva, John Adams, Yuriy Malozovsky We study the electron correlation in the armchair carbon nanotubes (CNT). We model the carbon nanotube as a tubule with electrons confined to the surface of the tubule by an attractive delta-function potential. We derived the dynamic pair interaction potential between two electrons in the tubule incorporating short-range and exchange correlation. Dispersion of plasma modes at different values of angular momentum and single-particle excitations are derived as well. We find that the plasma modes are not Landau damped and the lowest mode has acoustic behavior. We also evaluate the self-energy part due to the interaction of an electron with acoustic mode. We find that the multiple scattering of an electron on the plasma acoustic mode leads to the quasiparticle (plasmaron) that is the self-localized electron in the polarization well. [Preview Abstract] |
Friday, March 25, 2005 8:48AM - 9:00AM |
X25.00005: Dielectric constant enhancement by aligned carbon nanotubes in composites Jakub Rybczynski, Yang Wang, Brian Kimball, J.B. Carlson, Krzysztof Kempa, Zhifeng Ren We study dielectric properties of composites made of isolated, aligned metallic carbon nanotubes, uniformly distributed in a dielectric matrix. We focus on the radio-microwave frequency range. We find, that properties of these composites depend crucially on the separation, aspect ratio and orientation of the nanotubes. In general, we show that carbon nanotubes can be used to produce composites with large real part of the dielectric function and a moderate loss, at loading low enough to allow the composite to remain mechanically flexible. A detailed study of morphology, nano-structure, and dielectric properties of such composites will be presented. [Preview Abstract] |
Friday, March 25, 2005 9:00AM - 9:12AM |
X25.00006: Theory of Vibrations in Suspended Nanotubes Hande \"Ust\"unel, David Roundy, Tom\'as A. Arias Vibrations of nanotubes clamped at both ends and suspended over a gate have been studied recently\footnote{V. Sazonova, Y. Yaish, H. \"Ust\"unel, D. Roundy, T. A. Arias and P. L. McEuen, Nature {\bf 431}, 284 (2004)}. In this talk, we study theoretically the effects of various parameters such as slack and downward force on the vibrations of such a suspended nanotube. We model the nanotube as a one-dimensional continuum and present results exploring a wide range of system parameters. [Preview Abstract] |
Friday, March 25, 2005 9:12AM - 9:24AM |
X25.00007: Chirality dependence of Raman cross-section of carbon nanotubes Serguei Goupalov The chirality dependence for the cross-section of Raman scattering from the radial breathing mode of carbon nanotubes observed in recent experiments [S.K.~Doorn {\it et al.,} Appl. Phys. A {\bf 78}, 1147 (2004)] is explained using the empirical tight-binding method. It is shown that the transfer and overlap integrals usually neglected while accounting for the electron energy spectrum in carbon nanotubes play a crucial role in description of the electron-phonon coupling. [Preview Abstract] |
Friday, March 25, 2005 9:24AM - 9:36AM |
X25.00008: Functional group interactions with single wall carbon NT studied by ab-initio calculations Giancarlo Cicero, Jeffrey Grossman, Aleksander Noy, Giulia Galli With the goal of designing functionalized nanotube materials, recent AFM measurements have succeeded in determining the force between individual chemical groups an single-wall carbon nanotubes (SWCNT) [1]. In order to rationalize and understand these experimental results, we have performed Density Functional Theory calculations for a number of structural arrangements of model tips functionalized with the same groups as those used experimentally. Our calculations include full geometry optimization of the composite SWCNT/tip system as well as `pulling-out' simulations to compute interaction forces. We considered (14$\times $0), semi- conducting tubes, and AFM tips where modeled by a SiH$_{3}$CH$_{2}$-X molecule, with X- representing -CN, -CH$_{3}$, -NH$_{2}$ or -CH$_{2}$OCH$_{2}$. As X is varied, computed forces reproduce the same trend as that observed experimentally when n-doped SWCNT are considered; significantly different trends are observed for neutral and p-doped tubes. We propose that the polar solvent present in the experimental setup may be responsible for the n-doping of the nanotube suggested by our calculations. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [1] M.C. LeMieux \textit{et al}, preprint [Preview Abstract] |
Friday, March 25, 2005 9:36AM - 9:48AM |
X25.00009: Amphoteric Doping of Carbon Nanotubes by Encapsulation of Organic Molecules: Vincent Meunier, Bobby G. Sumpter, Robert J. Harrison The unique structural and electronic properties of carbon nanotubes provide a tremendous potential for applications in the field of molecular electronics. Practical realizations of new nanotube-based devices hinge on a number of outstanding problems, such as the capability in achieving large-scale air-stable and controlled doping. Recent experimental evidence [Nature Materials 2, 683,2003] suggests that amphoteric doping of single-walled carbon nanotubes is possible by using simple organic molecules possessing different electron affinities and ionization energies. In order to optimize and investigate the electronic transport processes in carbon nanotubes doped with organic molecules we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our results suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. [Preview Abstract] |
Friday, March 25, 2005 9:48AM - 10:00AM |
X25.00010: Structural, Elastic, and Electronic Properties of Deformed Carbon Nanotubes under Uniaxial Strain A. Pullen, G.L. Zhao, D. Bagayoko, L. Yang We report structural, elastic, and electronic properties of selected, deformed, single-wall carbon nanotubes under uniaxial strain. We utilized a generalized gradient approximation (GGA) potential of density functional theory and the LCAO formalism. We discuss bond-lengths, tubule radii, and the band gaps as functions of tension and compression strain for carbon nanotubes (10, 0), (8, 4) and (10, 10) which have chiral angles of 0, 19.1, and 30 degrees relative to the zigzag direction. We also calculated the Young's modulus and the in-plane stiffness for each of these three nanotubes as representatives of zigzag, chiral, and armchair nanotubes, respectively. We found that these carbon nanotubes have unique structural properties consisting of a strong tendency to retain their tubule radii under large tension and compression strains. Work funded in part by US NASA (Award No. NCC 2-1344). [Preview Abstract] |
Friday, March 25, 2005 10:00AM - 10:12AM |
X25.00011: Carbon Nanotubes under Hydrostatic Pressure: The Deformation Transition Marvin L. Cohen, Catalin D. Spataru, Steven G. Louie, Rodrigo B. Capaz, Paul Tangney Isolated single-wall carbon nanotubes (SWNTs) deform from their usual cylindrical shape to a collapsed or oval cross-section upon increase of hydrostatic pressure. We use classical molecular-dynamics simulations to study the structural properties of isolated SWNTs under pressure near this deformation transition. Within our model, we find two distinct behaviors depending on the nanotube diameter $d$. For $d > d_c \approx 12$ \AA, SWNTs collapse from a circle to a peanut or racetrack cross-section at a critical pressure $P_c$ with a discontinuous change in volume. The van der Waals interactions between the opposite walls of the tube play a crucial role in driving this discontinuous transition. For a range of pressures, both circle and collapsed cross-sections are locally stable and the system shows hysteresis. For $d < d_c$, the transition is continuous, from a circle to an oval cross-section. RBC acknowledges financial support from the John Simon Guggenheim Memorial Foundation and Brazilian funding agencies CNPq, CAPES, FAPERJ, Instituto de Nanoci{\^e}ncias, FUJB-UFRJ and PRONEX-MCT. This work was supported by NSF Grant No. DMR04-39768 and by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. DOE under Contract No. DE-AC03-76SF00098. Computational resources have been provided by NERSC and NPACI. [Preview Abstract] |
Friday, March 25, 2005 10:12AM - 10:24AM |
X25.00012: Velocity dependence of friction during relative sliding motion of finite concentric carbon nanotubes Paul Tangney, Stephen B. Fahy, Marvin L. Cohen, Steven G. Louie Carbon nanotubes are promising candidate materials for use in the construction of nanoscale mechanical devices. Indeed, some prototype mechanical elements such as linear and rotational bearings have already been realized experimentally. A crucial question for the ultimate functionalization of these devices is the efficiency with which they can operate. In this work the effects of friction on pristine nanotube-based mechanical devices are examined. Molecular dynamics simulations are used to study the rate and mechanism of dissipation of mechanical energy during relative motion (along the tube axis) of both capped and uncapped nanotubes moving inside a larger concentric carbon nanotube. A strong and complex dependence of dynamic friction on velocity is observed. Some unique features of friction in nanoscale devices are pointed out and it is shown how these features may be related to the observed behaviour. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. [Preview Abstract] |
Friday, March 25, 2005 10:24AM - 10:36AM |
X25.00013: Remarks on Edge States with the Aharonov-Bohm Flux Ken-ichi Sasaki, Yoshiyuki Kawazoe, Riichiro Saito, Shuichi Murakami It was shown theoretically that zigzag edges of graphite ribbon and of nanotube contain peculiar localized states whose energy eigenvalue exists between conduction and valence band. We point out that there are two critical edge states in metallic zigzag nanotubes whose localization length is sensitive to the mean curvature of a nanotube and they can be controlled by the Aharonov-Bohm flux along tubule axis. [Preview Abstract] |
Friday, March 25, 2005 10:36AM - 10:48AM |
X25.00014: Resonant Tunneling at Carbon Nanotube Telescope Junctions Young-Woo Son, Marvin L. Cohen, Steven G. Louie We present a first-principles study of the quantum conductance of carbon nanotube `telescope' junctions. The junctions consist of two partially overlapping concentric metallic or semiconducting carbon nanotubes. The quantum conductance of the open system is calculated using a newly developed scattering state approach~\footnote{Hyoung Joon Choi, Marvin L. Cohen, and Steven G. Louie, {\it to be published}} combined with {\it ab initio} electronic structure calculations. Localized states associated with the edges of each nanotube are found to contribute resonant tunneling channels and the resulting conductance spectra are very sensitive to the adsorption of gaseous particles. The spin-dependent conductances of semi-metallic $(3n,0)$ nanotube telescope junctions will also be discussed. This work was supported by NSF Grant No. DMR04-39768 and by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy under Contract No. DE-AC03-76SF00098. Computational resources have been provided by NPACI. [Preview Abstract] |
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