Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y26: Focus Session: Charge Transport in Nanostructures V |
Hide Abstracts |
Sponsoring Units: DCP Chair: Massimillimo Di Ventra, University of California, San Diego Room: Colorado Convention Center 205 |
Friday, March 9, 2007 11:15AM - 11:51AM |
Y26.00001: What are `molecular wires' and how might we use them? Invited Speaker: Through-bond tunneling is generally greatly enhanced over through-space tunneling, so organic `wires' can connect electrodes over distances with $>$nS conductance over distances of several nm. Very small decay lengths (or even non-exponential decay) suggest that mechanisms other than tunneling can contribute to transport. Wires made with electroactive (reducible/oxidizable) molecules can be gated electrochemically, and can be switched without any gate at all if the field owing to the applied bias is large enough, giving rise to switching and NDR. Wires that reconcile the competing requirements of flexibility (so they can be properly bonded) with high conductance will be useful elements in nanoscale devices and sensors. [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:03PM |
Y26.00002: Molecular conductance from density functional theory calculations Daniel Kosov, Zhenyu Li We will present a plane-wave/pseudopotential implementation of a method to calculate the electron transport properties of nanostructures. We performed density functional theory based electron transport calculations of amine, dithiocarboxylate and dithiiocarbamate anchored junctions. We demonstrated that the stronger molecule-electrode coupling associated with the conjugated dithiocarbamate linker broadens transmission resonances near the Fermi energy. The conductance enhancement factor is as large as 25 is predicted for dithiocarbame anchored junctions. A microscopic origin of the experimentally observed current amplification by dithiocarboxylate anchoring groups is established. We calculated the conductance traces for amine and thiol anchored junctions as the molecules are pulled by the STM tip from the Au electrode. Our calculations show that the stretching of the thiol anchored junction during its formation is accompanied by significant electrode geometry distortion. Oppositely, the electrode for the amine terminated junction remains intact when the junction is stretched by the STM tip. Z. Li and D. Kosov, J.Phys.:Cond.Matt. 18 (2006) p.1347; J.Phys.Chem B 110 (2006) p.19116, ibid p.9893 [Preview Abstract] |
Friday, March 9, 2007 12:03PM - 12:15PM |
Y26.00003: Exploring conductance switching properties of molecular scale devices - a computational approach. Barry D. Dunietz, Alexander Prociuk, Mousumi Das, Trilisa Perrine A computational approach is used and developed to study electron transport through molecular scale devices. The study identifies and provides insight into mechanisms underlying transport switching properties. These systems include: 1. Spin-dependent electronic transport through a Porphyrin ring Ligating an Fe(II) atom, 2. Contact geometry and orientation effects of conjugated molecular transistors and 3. Chemical sensors with focus on metal recognition properties recently exhibited only for certain short peptide chains. The research also involves developing new models and methods to describe electron conductance through single molecular systems. [Preview Abstract] |
Friday, March 9, 2007 12:15PM - 12:27PM |
Y26.00004: Measurement of Single Molecule Conductance Joshua Hihath, Xiulan Li, Fang Chen, Nongjian Tao Understanding the electron transport properties of single molecules is a basic requirement for achieving molecular-scale electronic devices reliable enough for everyday use. To help elucidate the transport mechanisms involved in various single metal-molecule-metal junctions we have performed measurements while applying an electrochemical gate, changing the environmental temperature, the chemical binding at the contacts, the bias, and the molecular length in an STM break junction system. Using this system and these handles to help elucidate conduction mechanisms we have explored several molecular systems, including simple alkane chains, conjugated redox molecules, and biologically relevant molecules such as DNA and proteins, in all cases we have gained some insight into the transport capabilities of each metal-molecule system. [Preview Abstract] |
Friday, March 9, 2007 12:27PM - 12:39PM |
Y26.00005: Statistical Analysis of Electronic Transport in Alkanethiol Molecular Devices with Nanowell Structures. Hyunwook Song, Takhee Lee, Nak-Jin Choi, Hyoyoung Lee We study charge transport through nanoscale molecular monolayers. For example, alkanethiol [CH$_{3}$(CH$_{2})_{n-1}$SH] self-assembled monolayer (SAM) is one of the most standard molecular systems that has been extensively investigated, and is very useful as a control in molecular devices because their structure and configuration have been sufficiently well-characterized. Reported here is a statistical analysis of electronic transport in alkanethiol SAM using different length alkanethiols. Particularly, we fabricated more than 6,000 molecular devices with nanowell structure, a vertical type of metal-molecule-metal junctions with nanometer scale junction diameter. We investigated transport properties such as temperature-variable current-voltage I(V,T) characteristics from these mass-fabricated devices. Based on the extensive I(V,T) data, a statistical analysis of transport characteristics in alkanethiol SAM will be presented. [Preview Abstract] |
Friday, March 9, 2007 12:39PM - 12:51PM |
Y26.00006: Electronic transport of low concentrations of P3HT molecules across nanogap source-drain electrodes. Jeff Worne, Behrang Hamadani, Douglas Natelson Poly 3-hexothiophene (P3HT) is a widely studied, versatile material used in organic electronics. Little is known, however, about the electronic transport properties of individual or small groups of P3HT molecules. Initial experiments suggest that the behavior of low concentrations of molecules differ significantly from bulk P3HT. We have fabricated nanoscale P3HT transistors using electromigrated nanogap structures as source-drain electrodes and the underlying silicon/SiO$_{2}$ substrate as a gate. We present preliminary transport data on these devices as a function of temperature and electrode material. [Preview Abstract] |
Friday, March 9, 2007 12:51PM - 1:03PM |
Y26.00007: Adsorption and conductance of BDT on the Au(111) surface A. Fazzio, Renato B. Pontes, Frederico D. Novaes, Antonio J.R. da Silva Molecular electronics is a new trend in the science and technology at the nanometer-scale. A prototypical system where transport properties have been widely studied both experimentally and theoretically is benzene-1,4-dithiolate (BDT) on Au(111). We present, using Total Energy Density Functional Theory calculations, a detailed study of such a system for different surface coverages and sites, and we find that except at high enough coverages, the BDT lowest energy configuration has the molecule almost lying down on the Au surface. We also find that when the BDT is bridging two Au(111) leads, this lying down configuration still has the lowest energy when compared to the standing up configuration (by approximately 0.4 eV). We have also calculated, using a DFT-based non-equilibrium Green's Function formalism, the conductance for a variety of BDT configurations, including how they vary as a function of the separation between the leads. We find that due to resonant features in the conductance, it can vary significantly depending on the distance between the leads. We also calculate the total energy, forces and conductance for a variety of BDT configurations for different separation between leads. We thank the Brazilian agencies FAPESP and CNPq, and CENAPAD-SP for computer time. [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:15PM |
Y26.00008: Ab-Initio calculations of electron transport properties of Si-Porphyrin-Si devices Filipe J. Ribeiro, Wenchang Lu, Jerry Bernholc We present results of numerical calculations of the electronic transport properties of devices consisting of porphyrin molecules connected to Si(100) leads. Our calculations are based on ab-initio ultrasoft pseudopotentials and the generalized gradient approximation (GGA) to the exchange and correlation energy functional. Transport properties were calculated using a non-equilibrium Green's function method in a basis of optimally localized orbitals. We studied three different molecules: H2-, Zn-, and Ni-porphyrins. The somewhat different alignments of the HOMO and LUMO levels of the molecules with the top of the valence and bottom of the conduction bands of the Si leads has strong implications on the I-V characteristics of the devices. In particular, the turn-on voltages are different for the different molecules. In addition, if the Si leads are heavily doped n-type, regions of negative differential resistance exist in all three systems. [Preview Abstract] |
Friday, March 9, 2007 1:15PM - 1:27PM |
Y26.00009: Role of dephasing and surface states in Si based molecular electronics Hassan Raza We study the effect of an unpaired dangling bond (DB) on occupied molecular orbital conduction through a styrene molecule bonded to a n++ H:Si(100)-(2$\times $1) surface. For molecules relatively far from the DB, we find good agreement with the reported experiment using a model that accounts for the electrostatic contribution of the DB, provided we include some dephasing due to low energy phonon modes. However, for molecules within 10{\AA} to the DB, we have to include electronic contribution as well along with higher dephasing to explain the transport features. Apart from this, we study the electronic band structure of unpaired and paired DBs, DB wires and clusters on H:Si(100)-(2$\times $1) surface using Extended H\"{u}ckel Theory (EHT) and report their effect on the Si band gap. An unpaired DB introduces a near-midgap state, whereas a paired DB leads to $\pi $ and $\pi $* states. The unpaired and paired DB wires introduce states in similar fashion however with larger dispersion. Furthermore, different DB clusters exhibit states that can be interpreted as superposition of states due to unpaired and paired DBs. (cond-mat/0607226,0611417) [Preview Abstract] |
Friday, March 9, 2007 1:27PM - 1:39PM |
Y26.00010: Time-Resolved, Single Molecule Spectroelectrochemistry of Conjugated Polymers in Contact with ITO John Grey, Rodrigo Palacios, Wei-Shun Chang, William Miller, Allen Bard, Paul Barbara Time-resolved, single molecule spectroelectrochemistry was used to study excited-state interfacial electron transfer between single conjugated polymer (MEH-PPV) molecules (possessing about 200 redox sites) and an indium tin oxide (ITO) electrode. Decay kinetics and emission yields were obtained while cycling the electrode potential in the range of -.5V to +.5V (Silver wire), which lies between the reduction (-1.5 eV) and oxidation potentials (0.8 eV) of the ground state. At +0.5 V, the emission intensities and average lifetimes were observed to increase about 20{\%} whereas at -0.5 V both values decrease by the same amount. Several possible origins of the potential-induced intensity modulation are proposed. [Preview Abstract] |
Friday, March 9, 2007 1:39PM - 1:51PM |
Y26.00011: Renormalized Couplings and the Insulator and Metallic Behavior of Double-Stranded DNA Efta Yudiarsah, Sergio E. Ulloa Electronic transport in double-stranded DNA is studied using a ladder model in a tight-binding Hamiltonian, withRealistic on- site energies [1] and hopping constants [2]. The effect of DNA molecules coupling to leads is studied on periodic poly (dG)-poly(dC) sequences with an embedded TGGGGT defect group. The differential conductance features diminish gradually and vanish at small coupling. The influence of counter-ions, local fields, and interaction with phonons can renormalize the hopping constants; we study the role of increasing intra-strand hopping on $\lambda$-phage DNA sequences. Increasing coupling results in the electronic transport of $\lambda$-sequences to change from insulator to metallic. Differential conductance $dI/dV$ at low bias is vanishingly small for bare hopping constants found in the literature [2], and increases rapidly if they are enhanced by more than 5 times. Even at large uniform intra-chain coupling (1 eV), $dI/dV$ drops drastically at low bias for sequences longer than 300 base pairs. Electron-phonon interactions are also considered. The diagonal (local) interaction results in polaronic effects while the non-diagonal terms yield phonon- assisted hopping. [1] S. Roche, Phys. Rev. Lett. 91, 108101 (2003). [2] A. A. Voityuk \emph{et al.}, J. Chem. Phys. 114, 5614 (2001). [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