Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P44: Focus Session: Nanoscale Transport - Metals |
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Sponsoring Units: DMP Chair: Doug Natelson, Rice University Room: Colorado Convention Center 507 |
Wednesday, March 7, 2007 11:15AM - 11:27AM |
P44.00001: Universal conductance fluctuations imply excess high frequency noise in mesoscopic gold wires. A. Trionfi, S. Lee, D. Natelson In cold, mesoscopic conductors, two-level fluctuators lead to time-dependent conductance fluctuations manifested as 1/f noise that are enhanced by quantum interference up to a universal limit (TDUCF). In Au nanowires, we measure the magnetic field dependence of TDUCF, weak localization (WL), and magnetic field-driven (MF) UCF before and after treatments that alter magnetic scattering and passivate surface fluctuators. Our coherence length data resolve a long-standing inconsistency between L$_{WL}$ and L$_{TDUCF}$, and may imply that fluctuators produce high frequency noise in excess of 1/f expectations. [Preview Abstract] |
Wednesday, March 7, 2007 11:27AM - 11:39AM |
P44.00002: Low Resistance Interfacing of Single-Crystal Gold Nanowires Birol Ozturk, Tetsuya D. Mishima, Daniel R. Grischkowsky, Bret N. Flanders We have developed an innovative approach to growing individual, single-crystal gold nanowires between targeted points on lithographic electrodes from simple salt solutions. This approach has allowed us to address a fundamental problem in nano-device-fabrication: the interconnecting of nanowires with external circuitry. That is, we have developed a Labview program which simultaneously controls a function generator and a sourcemeter. This program modulates the growth-inducing voltage to attain low contact resistances between gold nanowires and lithographic electrodes. Four-probe measurements revealed that the contact resistances of the electrode-nanowire-electrode assemblies are consistently less than 25 $\Omega $. To our best knowledge, the sub-25 $\Omega $ contact resistances are the smallest that have been attained by any single-step nanowire growth and interfacing approach. Thus, gold nanowires grown with this method are ideal for use as conducting lines in nanoelectronic and nanobiological applications. [Preview Abstract] |
Wednesday, March 7, 2007 11:39AM - 11:51AM |
P44.00003: Long Range Directional Growth of Electrochemical Nanowires Prem Thapa, Bret Flanders We report on the directional growth of crystalline metallic nanowires between targeted sites in on-chip circuitry. We observed that 200 nm diameter, needle-shaped wires grow between the electrodes after the deposition of 10 $\mu $l aqueous indium acetate solution and application of a 10 MHz alternating voltage. This effect occurs even when the electrodes are separated by as much as 100 $\mu $m. Hence, this effect is indicative of a long-range interaction, which is surprising given that this occurs in an electrolytic solution where Debye screening is expected. In this talk, we will discuss the possible origin of this long-range interaction. This capability provides an innovative way to interface multiple nanowires to a single cell membrane, enabling the future study electrophysiological events in live cells. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:03PM |
P44.00004: Scanning Tunneling Spectroscopy of Few-Atom Nb Nanoclusters on an Ultrathin Insulating Surface. C.D. Ruggiero, T. Choi, J.A. Gupta The study of small metallic clusters offers insight into the evolution of electronic structure from atomic orbitals to bulk-like band structure. We report scanning tunneling spectroscopy on small Nb clusters ranging in size from a single atom to a few atoms. All data were collected using a low-temperature ultrahigh vacuum scanning tunneling microscope operating at 5K. Insulating islands of CuN ($\sim $5nm x 5nm) were grown on a Cu(100) surface in order to decouple deposited Nb clusters from the metal substrate. Tunneling spectra on a bare CuN island reveal an insulating gap exceeding 4eV despite a thickness of only one monolayer. The dI/dV spectra of few-atom Nb clusters on CuN islands reveal a pronounced peak that may be associated with an atomic resonance. The peak position shifts in energy by as much as 0.5eV as a function of cluster size. http://www.physics.ohio-state.edu/$\sim $jgupta [Preview Abstract] |
Wednesday, March 7, 2007 12:03PM - 12:15PM |
P44.00005: Electron transport in magnetite nanoparticles Sungbae Lee, John T. Mayo, Vikki L. Colvin, Douglas Natelson Magnetite (Fe$_{3}$O$_{4})$ is an example of a strongly correlated, mixed valence oxide. Electron transport through small numbers of monodisperse magnetite nanocrystals (20nm in diameter) is measured on nanometer-scale three-terminal devices where nanoparticles are decorated on lithographically defined platinum electrodes. The abrupt development of discontinuities on IV curves around 120K and below strongly suggests the particles are going through the Verwey transition. Initial measurements of the full range of IV characteristics and magnetoresistive behaviors of these devices are presented. [Preview Abstract] |
Wednesday, March 7, 2007 12:15PM - 12:27PM |
P44.00006: Strong magnetic scattering from TiO$_{x}$ adhesion layers D. Natelson, A. Trionfi, S. Lee Electronic phase coherence in normal metals is incredibly sensitive to magnetic scattering. As a result, the weak localization magnetoresistance and time-dependent universal conductance fluctuations are powerful probes of magnetic impurities. We report measurements of these effects in Au and Ag nanowires, comparing samples with and without an underlying 1.5~nm thick Ti adhesion layer. Because of background oxygen, this layer is likely TiO$_{x}$, with $x < 2$. Samples with no adhesion layer show no sign of magnetic contamination. Samples with adhesion layers measured immediately after fabrication show clear evidence of strong magnetic scattering. Annealing in air reduces the concentration of scatterers, as does evaporation under conditions that encourage the formation of TiO$_{2}$. This strongly suggests that the magnetic scattering and its evolution are related to the oxidation state of the Ti, and is consistent with recent reports of ferromagnetism in oxygen-poor TiO$_{2-\delta}$. [Preview Abstract] |
Wednesday, March 7, 2007 12:27PM - 1:03PM |
P44.00007: Quantum Tunneling of Phase Slips in Al Nanowires. Invited Speaker: Superconductivity is a unique phenomenon which manifests itself, most strikingly, as the absence of electrical resistance at very low temperatures. While the resistance in 3-D Superconductors is exactly zero below the Normal-Superconducting transition temperature ($T_c$), in 1-Dimensional ones the proliferation of phase slips-- small regions which become normal allowing the phase of the order parameter to rapidly change by 2$\pi$-- can produce a residual resistance or destroy the superconductivity altogether. In the classical Langer, Ambegaokar, McCumber and Halperin theory, phase slips are caused by thermal excitation over free energy barrier that separates metastable states but Giordano suggested that Macroscopic Quantum Tunneling of phase slips through the barrier (Phys. Rev. Lett. 61, 2137 (1988)) could be significant at very low temperatures where thermally activated phase slips would be exponentially suppressed. However, despite intense experimental effort over the past 20 years, quantum tunneling of phase slips has remained controversial in 1-D superconductors. This talk will discuss the limiting case of 1-D superconductivity in an extremely long (100 $\mu$m) and narrow (5 nm--25 atoms) aluminum wire. In applied magnetic field, and at temperatures well below the superconducting transition, we find evidence ofm macroscopic quantum tunneling at temperatures where the classical theory of thermally activated phase slips would not be able to reproduce the experimental results (Phys. Rev. Lett. 97, 017001 (2006)). Not only are these results valid in linear regime, where most of the experimental data so far has been obtained, but they are consistent and supported by a newly proposed analysis in non-linear regime. These results help ruling out other scenario and establishing that, at temperatures much below $T_c$, the transport properties of superconducting 1-D nanowires are primarily determined by macroscopic quantum tunneling of phase slips. [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:15PM |
P44.00008: Observation of Josephson junction behavior in an individual superconducting NbSe$_{2}$ nanowire Zhixian Zhou, R. Jin, Gyula Eres, D. Mandrus, P. Schlottmann, Y.S. Hor, Z.L. Xiao, J.F. Mitchell Resistance and current-voltage characteristics of an individual superconducting NbSe$_{2}$ nanowire of 75 nm diameter were investigated employing four-probe transport measurements. With the absence of the dissipative motion of vortices, we find that the critical current is limited by a single asymmetric Josephson junction with unequal energy gaps across the junction and that their temperature variation is in excellent agreement with the BCS theory. The difference in the magnitude of the superconducting gap can be attributed to the existence of multiple Fermi surface sheets possessing different electronic structure and electron-phonon interactions. In addition, the temperature dependence of the critical current can be well described by the Ambegaokar-Baratoff relation. [Preview Abstract] |
Wednesday, March 7, 2007 1:15PM - 1:27PM |
P44.00009: Electric Field Effect Modulation of Charge Transport in Atomically Thin Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ Asher Mullokandov, Solomon Endlich, Joel Chudow, Yuanbo Zhang, Philip Kim We investigate the superconducting properties of mesoscopic Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (BSCCO) crystallites of thickness $\sim $2.5-4 unit cells. The crystals are mechanically extracted from the bulk, deposited on a silicon oxide substrate, and 4-probe measurements are conducted with gold contacts. In films that are 3 to 3.5 unit cells thick, the transition from the metallic to the superconducting state is observed at a critical temperature of $\sim $95K, while for 2.5 unit cell crystals the resistance versus temperature curve indicates semiconducting behavior. We also investigate resistance (conductance) variation and critical temperature shifting due to carrier density modulation via an applied gate field at temperatures from 300K to helium temperature. Electric field effect modulation of transport properties in these thin crystallites will be discussed in different temperature ranges. [Preview Abstract] |
Wednesday, March 7, 2007 1:27PM - 1:39PM |
P44.00010: Electron transport studies of superconducting Pb single-electron tunneling transistors Kang Luo, Dong-Hun Chae, Zhen Yao We investigate the electronic transport properties of superconducting Pb single-electron tunneling transistors created by electromigration of Pb nanowires. In the superconducting state, the conductance is suppressed due to the Coulomb blockade effect and the absence of density of states in the superconducting gap. Within the region of suppressed conductance, fine structures are observed which can be attributed to quasiparticle tunneling processes involving singularity matching. These features exhibit strong odd-even parity effect at 2 K and become smeared out at 4.2 K. Our preliminary results of single-molecule transistors using superconducting Pb electrodes will also be presented. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 1:51PM |
P44.00011: ABSTRACT WITHDRAWN |
Wednesday, March 7, 2007 1:51PM - 2:03PM |
P44.00012: Fabrication of Variable-Height Nanostructures via Dynamic Stencil Deposition Jeffrey Wasserman, Kristin Lucas, Soo Hyung Lee, Caitlin Crowl, Anthony Ashton, Nina Markovic Shadow masks of thin low-stress silicon nitride membranes with nanopore punctures allow for direct deposition of material with features as small as 10nm, without need for resists or other chemical exposure. We have built a device to translate the shadow mask with a nanopore relative to a substrate, allowing controllable nanoscale features to be `drawn' directly onto the substrate. By modulating the speed of the shadow mask we can vary the height of the nanostructure as it is being deposited. This allows for direct fabrication of nanowires and quantum dots, as well as controllable granular nanostructures and parallel arrays of nanostructures, not feasible using other techniques. We present in this talk our method for implementing nanoscale dynamic stencil deposition, as well as a variety of nanostructures and other components we have fabricated and studied via this deposition technique. [Preview Abstract] |
Wednesday, March 7, 2007 2:03PM - 2:15PM |
P44.00013: Sub-10 nm Device Fabrication in a High-Resolution Transmission Electron Microscope Michael Fischbein, Marija Drndic Materials are known to be susceptible to electron-irradiation induced damage during their imaging in a TEM. Though these effects are typically undesirable, we show here that electron-irradiation by the imaging beam of a HRTEM can be used to controllably sculpt metal with single-nanometer precision, thereby enabling device fabrication at a size scale that traditional fabrication methods cannot access. We have used this technique to fabricate metal structures with sub-10 nm features on silicon nitride membrane substrates. Examples include arbitrarily curved nanowires, nanometer-wide channels and nanorings. It will be shown that these ultra-small structures can be integrated into large-scale circuitry, without contact resistance. Potential applications of this technique include nanoelectronics, nanofluidics and the study of size effects on superconductivity. This work was supported by ONR Young Investigator Award (N000140410489), NSF Career Grant (DMR-0449553), NSF NSEC Grant (DMR-0425780), and NSF-IGERT (DGE-022166). [Preview Abstract] |
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