Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session P31: Nanotubes: Theory and Experiment |
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Sponsoring Units: DCMP Chair: Nicholas Kioussis, California State, Northridge Room: Baltimore Convention Center 328 |
Wednesday, March 15, 2006 11:15AM - 11:27AM |
P31.00001: Building and Deploying Community Nanotechnology Software Tools on nanoHUB.org -- Non-Equilibrium Green's Function Simulations of the Impact of Atomic Defects on the Performance of Carbon Nanotube Transistors. Neophytos Neophytou, Shaikh Ahmed, Diego Kienle, Mark Lundstrom, Gerhard Klimeck The Network for Computational Nanotechnology (NCN) is a multi-university, NSF-funded initiative with a mission to lead in research, education, and outreach deploying a unique web-based infrastructure (http://nanoHUB.org) to serve the nation's National Nanotechnology Initiative. Around 30 research codes/community tools are available and all the NCN services are free of charge. One such community tool is the CNTFET simulator based on NEGF techniques and the Finite-Element-Method (FEM) to treat three-dimensional (3D) electrostatics. We are able to simulate electronic transport in experimentally demonstrated 3D CNT devices with atomistic potential and charge resolution. Currently, we are investigating the effects of atomistic defects in the CNT devices such as vacancies and charged impurities. [Preview Abstract] |
Wednesday, March 15, 2006 11:27AM - 11:39AM |
P31.00002: Separation of single-walled carbon nanotubes into metallic and semiconducting groups: a simple and large-scale method Jing Lu, Y. Maeda Separation of a large number of single-walled carbon nanotubes (SWNTs) into groups each with specifically metallic and semiconducting properties is an extremely important task for technology application. Even though effective methods (1, 2) have been devised, they suffer from drawbacks such as either the yield is low (3) or expense is high (4). In this work, we study the problem from a theoretical approach, we notice that based on the first principles calculations the binding strengths of methylamine to the semiconducting [13, 0] SWNT are only 36$\sim$61\% of that to the metallic [7, 7] SWNT, which suggests that the amines is much more attractive toward the pure metallic than the semiconducting SWNTs. Therefore starting from as-prepared SWNTs and with the assistance of amines, we achieved SWNTs with enriched metallic properties over semiconducting in a convenient and large-scale manner. References: (1) D. Chattopadhyay, L. Galeska, F. Papadimitrakopoulos, Journal of the American Chemical Society 125, 3370 (MAR 19, 2003). (2) H. P. Li et al., Journal of the American Chemical Society 126, 1014 (FEB 4, 2004). (3) R. Krupke, F. Hennrich, H. von Lohneysen, M. Kappes, SCIENCE 301, 344 (JUL 18, 2003). (4) M. Zheng et al., Science 302, 1545 (NOV 28, 2003). [Preview Abstract] |
Wednesday, March 15, 2006 11:39AM - 11:51AM |
P31.00003: Polaron superconductivity model for Li-doped nanotube-zeolite composite Xianxiang Huang, Ping Sheng We propose a polaron superconductivity model for Li-doped nanotube-zeolite composite, in which the 4 Angstrom carbon nanotubes are embedded in the zeolite matrix, with a nanotube-nanotube wall separation of less than 10 Angstroms. The small separation implies inevitable nanotube-nanotube coupling, leading to a 3D anisotropic superconductor. Here we calculate the mean-field superconducting transition temperature based on the fact that each adsorbed Li atom, situated in the middle of the nanotube, donates an electron to the nanotube so as to form an ion-electron system. In addition, the Li ion is trapped in a shallow well formed by the (5,0) nanotube, with a periodicity of 4.3 Angstroms. So the Li vibration resembles that of an optical phonon. We have evaluated both the electron-electron interaction and the electron-phonon interactions in the presence of the screening effect, and solved the Eliashberg-Gorkov equation to obtain the superconducting transition temperature. [Preview Abstract] |
Wednesday, March 15, 2006 11:51AM - 12:03PM |
P31.00004: Theoretical Model for a Carbon Nanotube-Based Magnetometer at Non-Zero Temperatures Vladimir Dobrokhotov, Chris Berven We present a complete description of electronic current in metallic single-walled carbon nanotubes under the influence of axially oriented magnetic fields at nonzero temperatures. We include in our model [1] the diameter of the carbon nanotube, the temperature and length of the nanotube. We find that the current in a zigzag carbon nanotube that is metallic at zero magnetic field is strongly modulated by varying the magnitude of an axially oriented magnetic field. We use this property, to propose a design of a carbon nanotube based directional magnetometer that could be designed to sense magnetic fields from 1 T to 8 T and at temperatures from 0 K up to 100 K. [1] Vladimir Dobrokhotov and Christopher Berven, ``Electronic Transport Properties of Metallic CNTs in an Axial Magnetic Field at nonzero Temperatures: A Model of an Ultra-small Digital Magnetometer,'' accepted for publication 11-2005 Physica E [Preview Abstract] |
Wednesday, March 15, 2006 12:03PM - 12:15PM |
P31.00005: Effect of Short-Range Electron Correlation in Nanotubes Andrew Kinchen, Russell Selva, Yuriy Malozovsky We study the effect of short-range electron correlation in the zigzag and armchair carbon nanotubes (CNT). We derived the dynamic pair interaction potential between two electrons in the tubule incorporating Hubbard type local field factor. The dispersion of plasma modes at different values of angular momentum, and chirality angle and single-particle excitations are derived as well. We also evaluate the self-energy part due to the interaction of an electron with acoustic mode. [Preview Abstract] |
Wednesday, March 15, 2006 12:15PM - 12:27PM |
P31.00006: Electron Standing Waves in Semiconducting Carbon Nanotubes: Spatially-Resolved Scanning Tunneling Spectroscopy Se-Jong Kahng, Hajin Kim, Sungjun Lee, Young Kuk Electronic modulation patterns were observed, from the gap states of semiconducting single-wall carbon nanotubes, using spatially-resolved scanning tunneling spectroscopy. Some modulations show single peaks, with the period twice of the lattice constants, while others show double peaks.. Both modulations are localized within a few nano-meters, enclosed by exponential decay functions. The modulation patterns are well understood in terms of the squared wavefunctions, derived from the simple quantum mechanical potential well models. Our model can be applied to the bound states of metallic carbon nanotubes as well. [Preview Abstract] |
Wednesday, March 15, 2006 12:27PM - 12:39PM |
P31.00007: Electronic structure of carbon nanotubes adsorbed on Si(001) vicinal surfaces. S. Berber, A. Oshiyama We have investigated adsorption of carbon nanotubes on Si(001) vicinal surfaces using Density Functional Theory total energy and electronic structure calculations. Energetically favorable adsorption orientations and positions of carbon nanotubes were searched by total energy calculations, and detailed atomic structure of carbon nanotubes adsorbed at most probable adsorption sites have been obtained by full structure relaxation. Adsorption energy shows both direction and site dependence since the carbon nanotube form covalent bonds with the clean vicinal surface. Charge transfer between the nanotube and the surface happens mainly at the interface, which results in a quasi one-dimensional electron channel. Electronic states of carbon nanotube and silicon surface are highly rehybridized and mixed. A metallic carbon nanotube could behave as small gap semiconductor depending on adsorption site. Insertion of $sp^3$ bonded carbon atoms in $sp^2$ bond network introduces energy gap in electronic structure of the nanotube near Fermi level. This energy gap could be eliminated if there are surface states available for charge transfer. But such surface states are not available for particular nanotube directions, and non-metallic electronic structure appears. Dangling bond states of silicon surface, which appears as energy bands near the Fermi level, attracts electrons from the nanotube provided that these states are localized near the nanotube. Termination of surface dangling bonds in the vicinity of adsorbed nanotube could help tune the electronic properties of adsorbed nanotube. [Preview Abstract] |
Wednesday, March 15, 2006 12:39PM - 12:51PM |
P31.00008: The II-VI nanostructure zoo Philip Lindan, Samantha Lister We present predictions of a completely new family of nanotubes, related nanostructures and fullerene-like cages formed from the II-VI semiconductor mercury telluride. Our predictions are supported by first-principles calculations on the structures. The structures are remarkable in several ways: They are all more stable than the planar form of HgTe from which they are formed; they are radically altered from the tetrahedral bulk forms, and a strong interaction with the electronic structure results in a semimetal-semiconductor transformation; and for the larger armchair tubes isomerisation leads to striking structures formed from heavy modification of the tube, accompanied by large changes in the bandgap. For the nanotubes two simple rules for preferred coordination of Hg and the Hg-Te-Hg bond angles explain the structural stability of the nanotubes, and the formation of their exotic isomers. The cage structures are based upon the Archimedean and Platonic solids, where key requirements in terms of numbers of vertices, number of triangular faces and their connectivity determine the viable subset of structures. [Preview Abstract] |
Wednesday, March 15, 2006 12:51PM - 1:03PM |
P31.00009: Nonlinear ac conductivity of disordered Luttinger liquids Bernd Rosenow, Thomas Nattermann We consider low energy charge transport in one-dimensional electron systems with short range interactions under the influence of a random potential. At zero temperature, the linear ac conductivity vanishes like $\sim \omega^2 (\ln (1/\omega))^2$. Much less is known about the \emph{non-linear conductivity}. At zero temperature and frequency, charge transport is only possible by tunneling of charge carriers, which can be described by instanton formation. The nonlinear dc conductivity is characterized by $I \sim \exp( - \sqrt{E_0 / E}) $ provided the system is coupled to a dissipative bath [1]. Combining RG and instanton methods, we calculate the nonlinear ac conductivity and discuss the crossover between the nonanalytic field dependence of the electric current at zero frequency and the linear ac conductivity at small electric fields and finite frequency [2].\\[0.5cm] [1] S.~Malinin, T.~Nattermann, and B.~Rosenow, Phys. Rev. B {\bf 70}, 235120 (2004).\\[0cm] [2] B.~Rosenow and T.~Nattermann, accepted for publication in Phys. Rev. B; preprint cond-mat/0408042. [Preview Abstract] |
Wednesday, March 15, 2006 1:03PM - 1:15PM |
P31.00010: Renormalization of a single impurity potential of arbitrary strength in a Tomonaga-Luttinger liquid Kenji Kamide, Yuji Tsukada, Susumu Kurihara We study the renormalization flow of a single impurity potential of arbitrary strength in a Tomonaga-Luttinger liquid (TL). It is known that an impurity potential in TL is effectively renormalized by electron-electron interaction, with different manners in weak and strong potential limits for spin dependent models $K_{s}\neq1$. This fact strongly suggests that the fixed points of an impurity potential should shift as varying potential strength. In order to determine the scaling fixed points at arbitrary potential strength, we extend boundary bosonization scheme to the problem of arbitrary potential strength, and calculate the local density of states (LDOS) as a function of temperature and distance from the impurity. The impurity scaling flow is determined from the ratio between LDOS at the boundary and in the bulk. For $K_{s}=1 $, the phase boundary is given by $K_{\rho}=1$ irrespective of the potential. For $K_{s}\neq 1$, we find that the fixed points shift from $K_{\rho}\sim 2-K_{s}$ to $K_{\rho}=1/K_{s}$ as increasing the potential strength from $0$ to $\infty$. We also discuss how the scaling behavior appears in transport experiments. [Preview Abstract] |
Wednesday, March 15, 2006 1:15PM - 1:27PM |
P31.00011: Adsorbed monolayers on suspended single-walled carbon nanotubes Zenghui Wang, Jiang Wei, Robert Dormaier, Oscar Vilches, David Cobden A monolayer of adsorbates on a single-walled carbon nanotube presents the possibility of extending earlier studies of two-dimensional monolayer systems on graphite to the quasi-one-dimensional regime, by effectively imposing cylindrical boundary conditions. The monolayer can be detected either via its effect on the nanotube's conductance or by using the nanotube itself as a vibrating microbalance. Many adsorbates are known to affect the conductance, through a variety of mechanisms. Amongst these are O$_{2}$ and the noble gases Xe and Kr, whose phases and ordering on 2D graphite are well known. Our experiments so far have indicated that the presence of an O$_{2}$ layer on a nanotube close to liquid nitrogen temperatures can be detected using a threshold shift. We are now fabricating individual suspended nanotube devices with the initial aim of studying cylindrical commensurability effects on the phases of noble gases using the microbalance technique. [Preview Abstract] |
Wednesday, March 15, 2006 1:27PM - 1:39PM |
P31.00012: Superplastic single-walled carbon nanotubes J.Y. Huang, S. Chen, Z. Wang, K. Kempa, S.H. Jo, Y.M. Wang, G. Chen, M.S. Dresselhaus, Z.F. Ren Theoretical prediction on the maximum achievable tensile strain of a single-wall carbon nanotube (SWCNT) is less than 20{\%}, but experiments indicate a much lower attainable strain of less than $\sim $6{\%}. Here we report that, at temperatures of above 2000\r{ }C, SWCNTs deform superplastically, with a tensile elongation to failure nearly 280{\%}, and a diameter reduction of fifteen times. With this remarkable dimension change, the electronic property changes correspondingly from a metal with a pseudogap to a semiconducting state with a tunable gap up to 2 eV. Such superplastic deformation originates from plastic deformation mechanism dominated by the nucleation and motion of the kinks as well as atom diffusion in SWCNTs at high temperatures. Variable range hopping conduction is observed in the localized state due to scattering by point defects and kinks in the quasi-one-dimensional system. [Preview Abstract] |
Wednesday, March 15, 2006 1:39PM - 1:51PM |
P31.00013: Unoccupied electronic states of Multiwall Carbon Nanotubes Arrays Patricio H\"{a}berle, Samuel Hevia, Rodrigo Segura, Wladimir Ib\'{a}\~{n}ez We have grown multiwall carbon nanotube (MWCNT) arrays by CVD both from pyrolysis of Fe-Phthalocyanine and decomposition of Acetylene on Fe covered SiO$_{2 }$/Si(111) substrates. The characteristic diameter of the tubes is 50 nm for both type of samples. Even though the films show good alignment in the bulk, they do present some disorder of the tubes at the top of the films. Inverse photoemission spectra from these samples are similar to those obtained from HOPG. The main differences are in: the non existence of what has been recognized as an image charge state on graphite and some additional intensity very close to the Fermi level ($\varepsilon _{F})$. A similar intensity has been measured previously by photoemission in a symmetrical position with respect to $\varepsilon _{F}$. This increased metallic character could, at this point, be interpreted as defects from the closure of the tubes or as a manifestation of van Hove oscillations in the unoccupied density of states. [Preview Abstract] |
Wednesday, March 15, 2006 1:51PM - 2:03PM |
P31.00014: Electrostatics of Straight and Wiggly Nanotubes in External Electric Field Mikhail Raikh, Eugene Mishchenko Distribution of charge induced in a straight nanotube (NT) by external electric field parallel to the NT axis is found as a function of the NT length and radius. As the voltage drop along the NT exceeds the gap, positive and negative charge regions emerge at the NT ends. These regions are separated by a neutral strip at the NT center. External field is unscreened within the neutral strip, while it is strongly suppressed outside the strip. For a NT of a wiggly shape, the induced charge distribution represents alternating positively and negatively charged regions separated by neutral strips. [Preview Abstract] |
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