Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V24: Focus Session: Transport in Nanostructures VII: Si Interfaces and Carbon |
Hide Abstracts |
Sponsoring Units: DMP Chair: Michael Fuhrer, University of Maryland Room: Morial Convention Center 216 |
Thursday, March 13, 2008 11:15AM - 11:27AM |
V24.00001: Leakage current in deca-nano MOSFET by surface state hopping Hassan Raza, Edwin Kan Si surface states have been a topic of recent study [Nature 439, 703 (2006), PRB 76, 045308 (2007)]. In this work, we present transport calculations through these surface states, which result in a two-dimensional system. Among the systems being considered are: (1) pi and pi* states on Si(100):(2x1) surface with asymmetric dimer reconstruction, and (2) dangling bond wires along and perpendicular to the dimer row direction. Previously, we have reported the electronic structure of these systems in PRB 76, 045308 (2007). Here, we show that these states can give rise to significant current densities and hence may contribute to subthreshold leakage. Furthermore, the transport depends on the location of Fermi level with respect to the band edge and hence on the Fermi level pinning. We use EHT (extended Huckel theory) for the electronic structure and NEGF (non-equilibrium Green's function) formalism for the mean-field quantum transport. EHT has been applied to Si bulk and surfaces and gives quantitative agreement with experiments, e.g. band gap and band dispersions. [Preview Abstract] |
Thursday, March 13, 2008 11:27AM - 11:39AM |
V24.00002: Tunneling properties of ultra-thin SiO$_2$ barriers: a first-principles study Eunjung Ko, Hyoung Joon Choi We performed first-principles simulations of the electron tunneling through ultra-thin SiO$_2$ barriers in Si(100)/SiO$_2 $/Si(100) structures. The atomic structures of the Si/SiO$_2$ interfaces are generated by considering various silicon suboxide states observed in photoemission studies. For comparison, we also consider sharp Si/SiO$_2$ interfaces with dangling bonds. For each atomic structure, the tunneling conductance is calculated by a first-principles scattering-state method based on the {\em ab-initio} pseudopotentials and the density functional theory within the local density approximation. As a result we obtained the dependence of the tunneling probabilities on the oxide thickness and on the interfacial structures. Effects of the dangling bonds on the tunneling probabilities will also be discussed. Computational resource for this work is provided by KISTI under the 8th Strategic Supercomputing Support Program. [Preview Abstract] |
Thursday, March 13, 2008 11:39AM - 11:51AM |
V24.00003: C$_{60}$-based devices: large scale simulations and design X. H. Zheng, W. Lu, T. A. Abtew, V. Meunier, J. Bernholc C$_{60}$ is one of the most promising building blocks in the design of molecular devices, due to its spherical symmetry and structural reproducibility. In this work, the electron transport properties of two- and three-terminal devices built of C$_{60}$s are investigated. The C$_{60}$s are connected by alkane chains and then sandwiched between aluminum nanowires. The calculations are carried out using a massively parallel real-space multigrid O(N) implementation of density functional theory. The conductance and nonlinear I-V characteristics are evaluated by a nonequilibrium Green function method in a basis of optimally localized orbitals (W. Lu, V. Meunier, and J. Bernholc, PRL 2005). A conduction mechanism mediated by the LUMOs of the C$_{60}$ molecules is revealed. Due to the bias effect on the LUMO alignment, negative differential resistance (NDR) is observed in both two- and three-terminal devices at a very low bias. Since the LUMOs can be easily modified by molecular adsorption, the NDR position is tunable and can be used in sensor applications without the need for specific molecular receptors. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V24.00004: Quasiparticle Gaps of Nanostructures Weakly-Coupled to their Environments: The Case of C60/Metal Interfaces Jay Sau, Jeffrey Neaton, Hyoung-Joon Choi, Steven G. Louie, Marvin L. Cohen A new approach based on density functional theory is developed to calculate charging energies and quasiparticle energy gaps of molecular systems weakly-coupled to an external environment. The approach is then applied to the case of a C60 molecule adsorbed on the Au(111) and Ag(100) surfaces. For C60/Au(111), the calculated quasiparticle gap is reduced by 2.34 eV relative to the gas-phase, consistent with recent experiments. For the more strongly-coupled C60/Ag(100) system, the predicted gap is also reduced, but differs from experiment by 0.5eV. The discrepancy is identified as being due to screening due to charge transferred from the metal to the molecule and is resolved by solving an effective Anderson Hamiltonian within the GW approximation for the carriers in the HOMO and LUMO states, which results in an extra renormalization of the gap for the Ag(100) case. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V24.00005: ABSTRACT WITHDRAWN |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V24.00006: Electron-phonon scattering effects on transport properties of carbon nanotube devices using time-dependent wave-packet approach Hiroyuki Ishii, Nobuhiko Kobayashi, Kenji Hirose Single-walled carbon nanotubes have been expected as nanoscale electronic devices, because the nanotubes are very good conductors exhibiting ballistic transport properties. However, the electronic current is saturated by the electron-phonon coupling. To realize the application of carbon nanotube devices, understanding of the scattering mechanism is required. We investigated the electron-phonon coupling effect on the transport properties of the nanotubes with micron order channel length, using the time-dependent wave-packet approach under a tight-binding approximation [1]. The vibrational atomic displacements in real space are introduced through the time-dependent transfer energies. We solved the time-dependent Schr\"odinger equation and obtained the diffusion coefficients of the electronic wave packets. From these data, we can extract the mean free path and conductance. We clarified the difference of the phonon scattering effects on the conductance of the metallic nanotube and the semiconducting one. Furthermore we investigate the channel length dependence of resistance from ballistic to diffusive transport characteristics. [1] S. Roche \textit{et al.}, PRL 95 (2005) 076803 [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 12:39PM |
V24.00007: ABSTRACT WITHDRAWN |
Thursday, March 13, 2008 12:39PM - 12:51PM |
V24.00008: Electron transport through functionalized carbon nanotubes Nicolas Bruque, Rajeev Pandey, Md. Khalid Ashraf, Roger Lake Single molecule functionalization of single walled carbon nanotubes (CNT)s by B. R. Goldsmith, et. al. [1] and single molecule bridges of single wall CNTs by X. Guo, et. al. [2] are elegant examples of CNT contacts to individual molecules for electronic applications. CNTs are of the same physical size as the molecule they contact providing a well-defined covalent bond between CNT electrodes and a molecule. The above two systems are studied to determine how a chemical absorbate and linker influence transport through metallic CNTs. The first system consists of a stand alone metallic CNT with a single oxygen adsorption site, matching a proposed final chemical process for a HNO$_{3}$ oxidation and reduction process. The second system consists of a CNT-Amide-(CH)$_{n}$-Amide-CNT structure in which both CNTs are metallic. Transmission calculations, using our DFT (FIREBALL)-NEGF code show that the amide linker suppresses transmission compared to a direct CNT-polyene linkage studied in [3]. 1. B. R. Goldsmith, et. al., Science, \textbf{315}, 77 (2007). 2. X. Guo, et. al. Science, \textbf{311}, 356 (2006). 3. N. Bruque, et. al. Phys. Rev. B, \textbf{76}, 205322 (2007). [Preview Abstract] |
Thursday, March 13, 2008 12:51PM - 1:03PM |
V24.00009: Multiple Quantum Well Structures of Graphene Haldun Sevincli, Mehmet Topsakal, Salim Ciraci Based on first-principles calculations we predict that periodically repeated junctions of graphene ribbons of different widths form multiple quantum well structures having confined states. These quantum structures are unique, since both constituents of heterostructures are of the same material. The width as well as the bad gap, even the magnetic ground state for specific superlattices are modulated in direct space. Orientation of constituent ribbons, their width and length, the symmetry of the junction and their functionalization by adatoms are structural parameters to engineer electronic and magnetic properties of the quantum structure. Not only the size modulation, but also composition modulation such as the heterojunction of BN in honeycomb structure and graphene gives rise to confined states. Devices made from these graphene quantum structures display negative differential resistance. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V24.00010: Direct measurement of electric-field-screening length in thin graphite film H. Miyazaki, K. Tsukagoshi, S. Odaka, Y. Aoyagi, T. Sato, S. Tanaka, H. Goto, A. Kanda, Y. Ootuka Electric-field-screening length in thin graphite film has been clarified by means of dual gating method. Sandwich type device structure which two gate electrodes are situated over and beneath a graphite film was constructed with Al top electrode. The Al electrode naturally generates thin gate insulator at graphite/Al interface, which enables extremely low voltage operation. Ambipolar charge conduction in a graphite film can be tuned by both top and back gate voltages. A scan of the top gate voltage ($V_{tg})$ generates a resistance peak in the ambiploar response. The back gate voltage ($V_{bg})$ shifts the ambipolar peak depending on the graphite thickness. The shift is larger in thinner film. The thickness-dependent peak shift is clarified in terms of the inter-layer screening length $\lambda $ to the electric field in the dual-gated graphite film. We assume that the gate-induced carriers decay exponentially from both surfaces, and that the conductivity in each layer increases proportionally to the induced carrier density. Then the condition for the ambipolar resistance peak in $V_{tg}$ scan is obtained as a function of $V_{bg}$, $\lambda $, and the graphite film thickness $d$. Applying this model to the thickness-dependence, we obtained a screening length of 1.2 nm experimentally. [Preview Abstract] |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V24.00011: Surface Potentials and Layer Charge Distributions in Few-Layer Graphene Sujit Datta, Douglas Strachan, Eugene Mele, A.T. Charlie Johnson Elucidating the electronic interaction between an insulating substrate and few-layer graphene (FLG) films is crucial for graphene device applications. We have performed electrostatic force microscopy (EFM) of FLG films. Our measurements reveal that the FLG surface electrostatic potential increases with film thickness, approaching a `bulk' value for samples with five or more graphene layers - contrasting sharply with behavior expected for conventional conducting or semiconducting films. This is in quantitative agreement with the analytic predictions of a nonlinear Thomas-Fermi theory of the interlayer screening by graphene's relativistic low energy charge carriers. Furthermore, our measurements are able to resolve previously unseen electronic perturbations extended along crystallographic directions of stressed samples, likely resulting from long-range atomic defects. [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V24.00012: Valley contrasting physics in graphene: magnetic moment and topological transport Qian Niu, Di Xiao, Wang Yao We investigate physical properties that can be used to distinguish the valley degree of freedom in graphene systems with broken inversion symmetry. We show that the pseudospin associated with the valley index of carriers has an intrinsic magnetic moment, in close analogy with the Bohr magneton for the electron spin. There is also a valley dependent Berry phase effect that can result in a valley contrasting Hall transport, with carriers in different valleys turning into opposite directions transverse to an in-plane electric field. These effects can be used to generate and detect valley polarization by magnetic and electric means, forming the basis for the so-called valleytronics applications. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V24.00013: Quantum transport of 2D Dirac fermions: the 2D symplectic symmetry class of Anderson localization and the Z2 topological term Shinsei Ryu, Christopher Mudry, Hideaki Obuse, Akira Furusaki We discuss the quantum transport of the 2D non-interacting Dirac Hamiltonian, which, underlies theoretical descriptions of graphene and surface states of 3D Z2 topological insulators. For a random scalar potential type disorder, a Z2 topological term is derived in the non-linear sigma model encoding the physics of Anderson localization in the symplectic symmetry class. Unlike the Pruisken term (Chern integer) in the IQHE, the Z2 topological term cannot be expressed, in general, as an integral of a local quantity, but as a sign of the Pfaffian of a family of Dirac operators. The Z2 topological term has a significant effect on the renomalization group flow of the conductance. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700