Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session K16: Focus Session: Molecular-Scale Electronics II |
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Sponsoring Units: FIAP Chair: Ravindra Pandey, Michigan Technological University Room: Baltimore Convention Center 312 |
Tuesday, March 14, 2006 2:30PM - 2:42PM |
K16.00001: Inelastic scattering effects on single molecule spectroscopy: Consequences for Negative Differential Resistance Jason Pitters, Robert Wolkow The adsorption of styrene and cyclopentene on Si(100) has been studied with scanning tunneling microscopy and spectroscopy. Blinking of molecules in images and irregularities in current-voltage spectra and in current-time traces are analyzed. It is also shown that NDR-like features in IV spectra of both styrene and cyclopentene molecules are not consistently present.~Such erratic behavior cannot be accounted for by voltage controlled resonant alignment of adsorbate and substrate energy levels but is consistent with random configuration change driven by inelastically scattered electrons. These random processes, which include molecular rearrangement, desorption and/or decomposition occur with increasing frequency at larger voltage and current settings.~It is concluded that the molecules studied do not exhibit negative differential resistance due to a resonant tunneling mechanism. Conditions where resonant NDR may be observed are discussed. [Preview Abstract] |
Tuesday, March 14, 2006 2:42PM - 2:54PM |
K16.00002: Calculations of the structural, electronic and transport properties of self-assembled monolayers of porphyrins on the Si(001) surface Filipe J. Ribeiro, W. Lu, J. Bernholc Self-assembled monolayers (SAMs) of organic molecules on surfaces have very promising technological applications. The oxidation states of porphyrins are currently being explored to store charge in a controllable way, aiming at the development of multi-state molecular memories. We present the results of theoretical calculations on the structural, electronic and transport properties of chemisorbed porphyrins on a hydrogen-passivated Si(001) surface. Density-functional calculations were performed to optimize the structural parameters of the adsorbed porphyrins using a real-space multi-grid approach. Electron transport properties for a porphyrin molecule attached to two Si(001) leads were calculated using a non-equilibrium Green's function method in a basis of optimally localized orbitals. Our results show that the current, negligible at low voltages, exhibits a very strong non-linear behavior for bias voltages above 1.5 V, including multiple regions of negative differential resistance (NDR). The multiple NDRs may lead to multi-state molecular devices. [Preview Abstract] |
Tuesday, March 14, 2006 2:54PM - 3:06PM |
K16.00003: Theory of molecular hysteresis switch Mortko Kozhushner, Ivan Oleynik Molecular hysteresis switching has been recently observed in a series of experiments that measured the I-V spectrum of bipyridyl-dinitro oligophenylene-ethylene dithiol (BPDN) based molecular devices [1]. The experimental observations clearly show the presence of Coulomb blockade in single organic molecules that is responsible for the voltage-induced switching. We present the theory of the hysteresis switch which explains the non-linear hysteresis I-V characteristics based on the mechanisms of Coulomb blockade and the existence of two different molecular conformations of neutral and charged states of the molecule. [1] A.S. Blum, J.G. Kushmerick, D.P. Long, C.H. Patterson, J.C. Yang, J.C. Henderson, Y.X. Yao, J.M. Tour, R. Shashidhar, and B.R. Ratna, \textit{``Molecularly inherent voltage-controlled conductance switching''} , Nature Materials \textbf{4,} 167 (2005). [Preview Abstract] |
Tuesday, March 14, 2006 3:06PM - 3:42PM |
K16.00004: Theory of Molecular Electron Transport Invited Speaker: Thanks to the curiosity and devoted research of physicists and chemists over the past century and a half, electron transport in extended system has been a well understood phenomenon and has lead to today's all pervasive, monolithic, microelectronics technology. However, despite intense interest and ensuing research since the 1950s, an understanding of electron transport in confined systems, such as molecules and nano-scale atomic particles, remains limited. In this talk, I shall present an overview of our current understanding of the physics and chemistry of electron transport in molecules and at the molecule-solid interface. The effect of electronic structure, chemical bonding, physical dimension, stereochemistry, and external perturbation on molecular electron transport will be discussed. [Preview Abstract] |
Tuesday, March 14, 2006 3:42PM - 3:54PM |
K16.00005: Electrical and structural switching in [2]rotaxane molecular electronic devices Yong-Hoon Kim, William A. Goddard III In the effort to identify good candidates of molecular electronics, two-families of redox-controllable mechanically interlocked supramolecular complexes -- bistable catenanes and bistable rotaxanes -- have attracted much attention. Carrying out large-scale first-principles matrix Green function calculations combined with classical force-field molecular dynamics simulations, we study the charge transport properties of a monolayer of full (including stoppers) bistable rotaxane molecules in their realistic folded conformations. We will discuss (i) the universal nature of the identified switching mechanism in comparison with the [2]catenane device, (ii) the robustness of the switching signal with respect to thermal fluctuations, and (iii) the nature of molecule-electrode barriers that play an important role in inducing a structural switching between the bistable conformations of the molecule, a precondition of observing the electrical switching. [Preview Abstract] |
Tuesday, March 14, 2006 3:54PM - 4:06PM |
K16.00006: Low temperature transport study of the nitro molecules Nabanita Majumdar, Z. Martin, N. Swami, L. Harriott, Y. Yao, J. Tour, D. Long, R. Shashidhar Various research groups, including ours, have observed switching with memory behavior at room temperature from a monolayer of oligo(phenylene ethynylene) (OPE) molecules with a nitro sidegroup.$^{1,2}$. This switching behavior has the potential to be used in molecular electronic devices. However, the transport mechanisms of this ``nitro'' molecule are not well understood. Understanding the transport mechanisms of the nitro molecules may help identify the underlying cause of the switching behavior. We performed a systematic study of the transport characteristics of OPE molecules with and without a nitro side group in our nanowell test device$^{3}$ at various temperatures between 60K and 300K. We observed non-switching exponential current-voltage characteristics from OPEs without the nitro side group. The mechanism of transport was determined to be hopping with a transport barrier of 0.03$\pm $.01 V between 100K to 300K. Switching with memory behavior as well as non-switching exponential I-V characteristics were observed from the nitro molecules at various temperatures. The transport mechanism in switching devices was determined to be hopping with an activation barrier of 0.26$\pm $.08 V between 200K and 300K. However, a significantly lower activation barrier similar to that of OPEs without a nitro group was estimated for the nitro molecule devices that did not show any switching behavior. [Preview Abstract] |
Tuesday, March 14, 2006 4:06PM - 4:18PM |
K16.00007: Theoretical Study of Spin-Polarized Electron Tunneling via C$_{60}$ Molecules Haiying He, Ravindra Pandey, Shashi Karna The controlled injection and transport of spin-polarized electrons through organic molecules has drawn increasing attention in recent years due to its potential applications in molecular and molecular-nano hybrid electronics and sensors. In this talk, we will present the results of a theoretical study of spin-polarized electron tunneling via C$_{60}$ molecules in contact with ferromagnetic nickel electrodes. In this system, the resistance varies as the magnetic moments in the two electrodes are tuned from parallel to anti-parallel alignment. Particular attention is given to the chemical bonding features in the molecule-electrode interface, which leads to the observed difference in magnetoresistance. [Preview Abstract] |
Tuesday, March 14, 2006 4:18PM - 4:30PM |
K16.00008: Is Electron Transport In Boron Nanotube Ballistic? Kah Chun Lau, Ranjit Pati, Ravindra Pandey, Shashi P. Karna The electron transport in single-walled boron nanotube is studied using the Landauer-Buttiker multi-channel approach in conjunction with the tight-binding method. The calculated results predict a ballistic transport in boron nanotubes, with a relatively lower resistances as compared to that of a single-walled carbon nanotube. The electron-deficient character in bonding of elemental boron may be attributed to its higher conductivity. [Preview Abstract] |
Tuesday, March 14, 2006 4:30PM - 4:42PM |
K16.00009: Active Transport Orbitals in Electron Propagator Calculations on Molecular Wires. Yuri Dahnovsky, V.G. Zakrzewski, Alexey Kletsov, J.V. Ortiz \textit{Ab initio} electron propagator methodology may be applied to the calculation of electrical current through a molecular wire. A new theoretical approach is developed for the calculation of the retarded and advanced Green functions in terms of the electron propagator matrix for the bridge molecule. The calculation of the current requires integration in a complex half-plane for a trace that involves terminal and Green function matrices. Because the Green function matrices have complex poles represented by matrices, a special scheme is developed to express these ''matrix poles'' in terms of ordinary poles. An expression for the current is derived for a terminal matrix of arbitrary rank. For multi-terminal terminals, the analytical expression for the current is given in terms of pole strengths, poles and terminal matrix elements of the electron propagator. It is shown that Dyson orbitals with high pole strengths and overlaps with terminal orbitals are most responsible for conduction of electrical current. [Preview Abstract] |
Tuesday, March 14, 2006 4:42PM - 4:54PM |
K16.00010: Electron Propagator Calculations on Molecular Wires. J.V. Ortiz, V.G. Zakrzewski, Alexey Kletsov, Yuri Dahnovsky Several molecular wires are studied by an \textit{electron propagator }method using a non-self-consistent formalism for the calculation of Keldysh functions. This approach is based on diagrammatic approximations for describing electron correlation in a bridge molecule that have been successful in the \textit{ab initio} determination of electron binding energies. In this work, we compute nonequilibrium Keldysh functions in order to find the dependence of current on applied voltage for particular molecular wires. Quantum chemical calculations are performed for several molecular bridges and require additional computational method development of established electron propagator techniques. The extended molecule approach is adopted. Results are compared with experimental data and other quantum chemical approaches, especially those based on density functional theory. [Preview Abstract] |
Tuesday, March 14, 2006 4:54PM - 5:06PM |
K16.00011: Molecular conductance at finite voltage: bias driven evolution of Kohn-Sham-orbitals Max Koentopp, Ferdinand Evers, Kieron Burke Ground state density functional theory calculations yield the exact electron density if the exact exchange-correlation functional is employed. The evolution of the equilibrium density with parametric changes in the Hamiltonian, e.g.\ realized by a change in the electrostatic potential, can provide crucial information about transport properties, like the Coulomb blockade. To test our ideas, we perform model calculations using the quantum chemistry package TURBOMOLE for a diode molecule, which exhibits the structure of a double quantum dot and has been investigated experimentally [1]. In particular, we explain the origin of the characteristic peak structure in the differential conductance. Our results are consistent with the interpretation that the stepwise increase of the conductance occurs when the number of occupied levels of one of the dots, that have an energy above the lowest unoccupied level of the other dot, increases by one.\newline \newline [1] M. Elbing, R. Ochs, M. Koentopp, M. Fischer, C. von H\"anisch, F. Weigend, F. Evers, H. Weber, M. Mayor, Proc. Nat. Acad. Sci. USA {\bf 102}, 8815 (2005). [Preview Abstract] |
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