Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session V39: Focus Session: Negative Differential Resistance I |
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Sponsoring Units: FIAP Chair: Udo Pernisz, Dow Corning Corporation Room: Colorado Convention Center 502 |
Thursday, March 8, 2007 11:15AM - 11:51AM |
V39.00001: Negative Differential Resistance Phenomena in Molecular Metal-Insulator-Metal Junctions Invited Speaker: Negative-differential-resistance (NDR) phenomena have been observed in metal-insulator-metal (MIM) junctions composed of various materials and are of interest because of their potential for producing bistability, oscillation, and gain in electronic circuitry. Recently, NDR has been observed by a number of different techniques in molecular MIM junctions based on self-assembled monolayers of nitro-substituted oligo(phenlyene-ethynylene) (OPE). Like NDR in other MIM systems, the mechanism behind the NDR in molecular MIM junctions is not well understood. We have recently investigated Hg-C14//OPE-Au bilayer molecular junctions that exhibit stable NDR characteristics over many bias sweeps, thereby permitting a systematic study of this effect. Our results on the variation of NDR peak with sweep rate, the charge flow during the NDR branch, the current-voltage characteristic for cyclic sweeps and other details of the characteristics suggest that the NDR is caused by charge storage (oxidation or reduction) within the junction that acts to modify the effective tunneling parameters. Quantitative estimates of the stored charge, the tunneling barrier height and effective mass also support this basic physical picture. These results will be compared with those for other MIM junction systems and discussed in the context of proposed mechanisms for this system. The physical picture developed here should be useful for understanding molecular MIM junctions at a fundamental chemical level. [Preview Abstract] |
Thursday, March 8, 2007 11:51AM - 12:03PM |
V39.00002: Characterization of Electrical Devices Based Upon Organic Monolayers Directly Attached to Si. C.A. Richter, C.A. Hacker, N. Gergel-Hackett, L.J. Richter, T.C. Allison, V. Mujica, C.A. Gonzalez We present the results of electrical measurements of alkane monolayers directly attached to Si-substrates. Molecular electronic test structures consisting of thiol or alcohol terminated molecules covalently attached via UV-assembly to Si (n-type, p-type, $<$100$>$, or $<$111$>)$ in oxide defined ``wells'' were characterized by capacitance-voltage and current-voltage (IV) measurements. These results are compared to models based on a first-order expansion of the system's Green function and a new method for the Si-molecule contact that predict a negative differential peak in the IV measurements due to an alignment between the Fermi energy of the Si substrate and the molecular LUMO. The structure of the molecular monolayers under full metallization was assessed with a novel backside incident FTIR technique and depth-profiling XPS. Au fully displaces the molecular monolayers (and forms a silicide), while Ag does not react with the underlying Si and forms a Ag/molecule/Si junction. [Preview Abstract] |
Thursday, March 8, 2007 12:03PM - 12:15PM |
V39.00003: Voltage-controlled non-linear characteristics of interdigitated MIM devices Bonnie Ludwig, Alex Hegyi, Christopher Kelly, Damian Khan, Mark Banaszak Holl, Bradford Orr Self-assembly was key to creating the first metal-molecule-metal (M-mol-M) junctions in Au-(HSiO$_{1.5})_{n}$-Au devices. Metal-insulator-metal (MIM) junctions are simple thin-film devices that, after application of an electroforming pulse, self-assemble into a system of conductive critical links. Electroforming causes the voltage-controlled response of the device to change from ohmic behavior to an unusual combination of nonlinearities including negative differential resistance (NDR), multiple rewriteable resistance states, and random telegraph signal (RTS) noise. The specific physical or chemical changes that cause these effects are unknown. Certain Au-(HSiO$_{1.5})_{n}$-Au devices have voltage-controlled behavior that is indicative of a reduced number of critical links. A comparison of the electronic behavior of MIM devices on two different size scales will be presented that provides further insight into the nature of individual critical links in these devices. [Preview Abstract] |
Thursday, March 8, 2007 12:15PM - 12:27PM |
V39.00004: Scanning Probe Microscopic Characterization of Electronic Properties of Self-Assembled Organic Monolayers on Au Surface Govind Mallick, Shashi Karna The surface ordering and electronic properties of $\sigma $-bonded 1-dodecanethiol molecules and a series of $\pi $-bonded molecules of comparable length self-assembled on Au-on-mica surface have been studied by atomic force and scanning tunneling microscopic measurements. The molecular-level surface-probe microscopic images show a higher degree of ordering in the monolayers of $\sigma $-bonded molecule compared to that of the conjugated $\pi $ molecules. This is explained in terms of a larger molecular volume and intermolecular repulsion in the later than the former. Electronic measurements reveal, as expected, a higher tunnel current in the $\pi $-bonded molecules compared to $\sigma $-bonded molecules. [Preview Abstract] |
Thursday, March 8, 2007 12:27PM - 12:39PM |
V39.00005: Absolute Negative Resistance Induced by Directional Electron-Electron Scattering in a Two-Dimensional Electron Gas Ismet I. Kaya A ballistic conductor is restricted to have positive three terminal resistance just as a Drude conductor. Intercarrier scattering does not influence the conductivity of the latter transport regime and does not exist in the former. However, as the electron energies increased, in the intermediate regime, single or few intercarrier scattering events starts to dominate the transport properties of a conductor with sufficiently small dimensions. A three-terminal device formed by two electrostatic barriers crossing an asymmetrically patterned two dimensional electron gas displays an unusual potential depression at the middle contact, yielding absolute negative resistance. The device displays momentum and current transfer ratios that far exceed unity. The observed reversal of the current or potential in the middle terminal is interpreted as the analog of Bernoulli's effect in a Fermi liquid. The results are explained by directional scattering of electrons in two dimensions. [Preview Abstract] |
Thursday, March 8, 2007 12:39PM - 12:51PM |
V39.00006: Resonant tunnelling assisted electrical switching in amorphous-carbon multilayer-superlattice structures Somnath Bhattacharyya, S. R. P. Silva Negative differential resistance (NDR) in an amorphous carbon (a-C) double barrier resonant tunnel diode (DB-RTD) with an estimated cut-off frequency well into the gigahertz regime is reported [1]. Presently we extend this work in carbon multi-layer superlattice structures by showing room temperature resonant tunnelling and establish a high value of the phase coherence length of $\sim $10 nm for low-dimensional amorphous materials. By applying a high bias, these structures are modified with reversible current switching of up to four orders of magnitude with a NDR signature and multiple peaks representative of resonant tunnelling in the ON state. In addition to the formation of filamentary channels by applying high bias, all these features are also explained using concepts based on tunnelling through the interface of the carbon layers, quantum-dot heterostructures and the presence of a confined two dimensional electron gas. This switching behavior and its tunability have been tested by applying a microwave signal up to 100 GHz which suggest the potential for novel high-speed memory devices. [1] S. Bhattacharyya, S.J. Henley, E. Mendoza, L.G-Rojas, J. Allam and S.R.P. Silva, Nature Mater. \textbf{5}, 19 (2006). [Preview Abstract] |
Thursday, March 8, 2007 12:51PM - 1:03PM |
V39.00007: Negative Differential Resistance in Covalently-Bridged Carbon Nanotube Junctions K.H. Khoo, Y.-W. Son, Marvin L. Cohen, J.B. Neaton, Steven G. Louie Recently, negative differential resistance (NDR) was observed in IV characteristics of carbon atomic wires connected across multi-wall carbon nanotubes.$^{1}$ Motivated by these results, we calculated IV characteristics of carbon atomic wires covalently bridging capped single-wall armchair carbon nanotubes using an \textit{ab-initio} scattering-state formalism based on density functional theory.$^{2}$ Our calculations for carbon chains with an odd number of atoms yield currents orders of magnitude larger than that of even chains, demonstrating clear even-odd behavior. We also observe NDR for odd chains and shorter even chains, in agreement with experiment. The current drop at higher voltages is attributed to an energy mismatch between localized nanotube ``cap states'' on different leads, possibly a generic feature of carbon nanotube molecular junctions. [1] T. Yuzvinsky \textit{et al., Nano Lett.} 10.1021/nl061671j (2006). [2] H.J. Choi, M.L. Cohen and S.G. Louie, to be published. This work supported by NSF Grant No DMR04-39768 and DOE Contract No DE-AC02-05CH11231. Computational resources from NERSC and SDSC. [Preview Abstract] |
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