Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S35: Molecular Electronics II |
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Sponsoring Units: DCP FIAP DMP Chair: Edwin Chandross, Bell Labs Room: LACC 511B |
Wednesday, March 23, 2005 2:30PM - 3:06PM |
S35.00001: Phonon effects in molecular conduction junctions Invited Speaker: This talk will give an overview of our work on effects of electron-phonon coupling on molecular conduction, including dephasing, dissipation and heating, then describe some recent observations, interpretations and predictions on three phenomena involving phonons in molecular junctions: (a) Heat conduction and its rectification by molecular wires$^{1,2}$; (b) inelastic electron tunneling spectroscopy$^{3-5}$ and (c) phonon-induced multi-stability, hysteresis and negative differential resistance in molecular conduction.$^{6}$ $^{1}$ D. Segal, A. Nitzan and P. H\"{a}nggi, J. Chem. Phys.\textbf{ 119, }6840-6855 (2003) $^{2}$ D. Segal and A. Nitzan, cond-mat/0405472 $^{3 }$M. Galperin, M. Ratner and A. Nitzan, J. Chem. Phys. \textbf{121}, 11965-11979 (2004) $^{4}$ M. Galperin, M. Ratner and A. Nitzan, Nano Lett., \textbf{4}, 1605-1611 (2004) $^{5}$ M. Galperin, A. Nitzan, M. A. Ratner and D. R. Stewart, to be published http://atto.tau.ac.il/$\sim $nitzan/253.pdf $^{6}$ M. Galperin, M. A.Ratner and A. Nitzan, Nano Letters, in press http://atto.tau.ac.il/$\sim $nitzan/254.pdf [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:42PM |
S35.00002: Charge injection and transport in a single organic monolayer island Invited Speaker: We report how electrons and holes, that are locally injected in a single organic monolayer island (where organic monolayers are made from sublimated oligomers (pentacene and other oligoacenes), or made from chemisorption in solution (self-assembled monolayers) of pi-conjugated moieties), stay localized or are able to delocalize over the island as a function of the molecular conformation (order vs. disorder) of this island. Charge carriers were locally injected by the apex of an atomic force microscope tip, and the resulting two-dimensional distribution and concentration of injected charges were measured by electrical force microscopy (EFM) experiments. We show that in crystalline monolayer islands, both electrons and holes can be equally injected, at a similar charge concentration for symmetric injection bias conditions, and that both charge carriers are delocalized over the whole island. On the contrary, charges injected into a more disordered monolayer stay localized at their injection point. These different results are discussed in relation with the electrical performances of molecular devices made from these monolayers (OFET, SAMFET). These results provide insight into the electronic properties, at the nanometer scale, of these molecular devices. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 4:18PM |
S35.00003: Electrical and Spectroscopic Characterization of Metal-Molecule-Metal Junctions Invited Speaker: Considerable attention has been devoted to developing an understanding of the mechanisms that dominate electrical transport in metal- molecule-metal junctions comprised of single and small ensembles of molecules. In this talk, we will present an overview of recent research on the electrical and spectroscopic characterization of molecular junctions inserted along the length of sub-40-nm diameter Au and Pd metal nanowires (i.e., in-wire junctions) fabricated by template-directed synthesis. In particular, we will show results that investigate the relationship between the temperature dependent (10 -- 300 K) current-voltage (I-V) characteristics and the vibrational spectra measured by inelastic electron tunneling (IET) spectroscopy for candidate molecular wires and bistable switching molecules. The two types of molecular wire junctions that were studied incorporate a self assembled monolayer of dithiolated oligo(phenylene- ethynylene) (OPE) molecules or their -NO$_{2}$ derivatives. The I-V of these junctions are stable and reproducible between +/-1V. Temperature independent I-V are measured for both types of junctions, which is indicative of coherent tunneling transport. Moreover, strong vibrations associated with $\upsilon $(18b) and $\upsilon $(19a) ring modes were observed in both junctions. In contrast, measurements of molecular junctions that incorporate SAMs based on aniline derivatives show reproducible bistable switching with an on-off ratio of $>$10:1 at 1V. Differences are observed in the vibrational spectra that depend on the state of the junction. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S35.00004: Critical Roles of Metal-Molecule Contacts in Electron Transport Through Molecular-wire Junctions Anton Grigoriev, Jonas Skoldberg, Goran Wendin, Zeljko Crljen We use non-equilibrium Green's function DFT methods (TranSIESTA) to study the bonding-site dependence of the transmission through metal-molecule contacts in molecular junctions of type M-S-mol-S-M for a number of different molecular systems, mainly short molecules with DTB as a reference system, and also OPVn, n=3-5. For all systems on Au(111) surfaces the transmission is quite insensitive to the bonding site. However, if S is adsorbed in an Au vacancy, or on- top of a small (3-Au-atom) island, the transmission can drop very substantially due to mismatch and changes of the HOMO structure in the contacts. However, we do not find any examples of several orders-of-magnitude reductions of the conductivity. In several systems with low zero-bias transmission at the Fermi level, we found that buried Au-S contacts (S adsorbed in Au vacancy) are associated with very sharp LUMO levels just above the Fermi level. Such a system will show extremely strong non-linear effects and might work as uni- or bi-directional voltage-controlled 2-terminal switches. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S35.00005: A Physical Interpretation of an Orhtogonal Hiolbert-Space Transformation: Transmision Antiresonances from Long-Range Hopping Seth Rittenhouse, Brad Johnson We provide the physical interpretation for a recently- introduced Hilbert space transformation from a nonorthogonal (overlapping) basis to an orthogonal basis, for the purpose of studying transport through single-molecule systems. The new Hilbert space may be interpreted as an orthogonal basis in the same {\it physical} space, wherein the basis overlap is formally transferred to the hopping matrix elements in the orthogonal system, resulting in a standard tight-binding system in an orthogonal basis with long-range hopping. We utilize the formal procedure to solve for the transmission characteristics of an impurity site (molecule) coupled with semi-infinite leads. We demonstrate that (previously predicted) transmission antiresonances are produced, in the orthogonal space, by the presence of second-nearest neighbor hopping. The parameter range in which transmission antiresonances are possible is formally outlined--a feature of the orthogonal space transformation. [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S35.00006: How does thermal motion of atoms influence rates of bridge-mediated electron transfer reactions? 1. Dynamical modulation of the effective tunneling coupling. Ilya Balabin, Spyros Skourtis, Tsutomu Kawatsu, David Beratan Understanding how thermal nuclear motion affects the electron transfer (ET) reaction rates is essential for describing a broad range of vital biological redox reactions as well as designing molecular electronic devices. Theoretical studies of biological ET reaction rates usually assume a) the superexchange ET regime (virtual bridge electronic states), and b) the Franck-Condon approximation (electronic dephasing slower than the time-dependent Franck-Condon factor decay time). We present the first investigation of the electronic dephasing effects and the first quantitative analysis of the modulation of effective tunneling coupling by nuclear dynamics. Molecular dynamics simulations coupled with extended Huckel-level quantum chemical calculations of the effective electronic coupling were performed for the blue copper ET protein azurin. We discuss effects of the donor-to-acceptor distance, tunneling pathway structure, tunneling energy, temperature, and protein motion on the dynamics of the effective tunneling coupling and the ET reaction rate. [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S35.00007: Direct Observation of a Molecular Junction using High-Energy X-ray Reflectometry Julian Baumert, Michael Lefenfeld, Eli Sloutskin, Moshe Deutsch, Colin Nuckolls, Ben Ocko Very little is known about the structure of organic molecular thin films at their rest potential. Further, it is not known whether the structure of these films is modified by an applied potential. We present a new x-ray scattering technique, which allows high-resolution structural studies of buried self-assembled monolayers (SAMs) that are sandwiched between silicon and mercury junctions. The high-energy x-ray beams, utilized in the present studies (32 keV), penetrate through the conducting silicon electrode. The x-ray reflectivity interference pattern thus provides information on the thickness and orientation of the molecules in the electronic junction. Our results, for alkane-thiol and alkane-silane layers, show that the SAMs form homogenous densely packed monolayers within the deeply buried interface. The thickness of these layers is compared with the SAMs prepared at the vapor/vacuum interfaces on mercury and silicon. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S35.00008: Programmable logic in the nanocell Jonas Skoldberg, Goran Wendin The investigated nanocell is a two-dimensional network of self- assembled metallic particles connected by molecules that show reprogrammable (i.e. can be switched between high and low conductance states) negative differential resistance (NDR). The nanocell is surrounded by four lithographically defined I/O leads at the edges of the nanocell. By selectively turning molecules on and off, the nanocell can be programmed to implement a set of logic gates. So far, no methods for programming the nanocell by only applying voltages to the access leads have been demonstrated (1). Using the nanocell circuit model described in (1), we will show that there is set of simple target circuit diagrams that implement the logic gates required for the architecture also described in (1). We will then show that the target circuit diagram is simple enough to, under certain assumptions, allow the nanocell to be programmed by applying voltages to the I/O pins. 1. C Husband, S Husband, et al. (2003). ``Logic and memory with nanocell circuits." IEEE Transactions on Electron Devices 50(9): 1865- 1875. [Preview Abstract] |
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S35.00009: Non-volatile multilevel Memory Based on Nanowire / Molecule Heterostructures Chao Li, Bo Lei, Wendy Fan, Chongwu Zhou A multilevel molecular memory device was constructed by coating In$_{2}$O$_{3}$ nanowire FETs with a self-assembled monolayer of Fe$^{2+}$-terpyridine compound. This bottom-up process takes advantage of both the nanowire and the redox-active molecules, as discrete multilevels naturally exist in an ensemble of redox-active molecules, while precise charge sensing can be carried out with a semiconducting nanowire transistor. In the demonstration, charges were precisely placed at up to eight discrete levels by altering the population of reduced / oxidized molecules. Gate voltage pulses and current sensing were used for writing and reading operations, respectively. More importantly, these devices exhibited ultralong retention up to 600 hours and great reliability. This approach solved the long-standing reliability issue by moving molecules outside the conduction path, and multilevel memory represents a conceptual breakthrough for molecular devices. [Preview Abstract] |
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