Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z6: Nanotubes and Nanowires (non-carbon): Other Phenomena |
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Sponsoring Units: DCMP Chair: Yanjie Zhou, Purdue University Room: 302 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z6.00001: Thin-Film Nanowire Networks for Transparent Conductor Applications: Simulations of Sheet Resistance and Percolation Thresholds Karen I. Winey, Rose M. Mutiso, Michelle C. Sherrott, Aaron R. Rathmell, Benjamin J. Wiley Thin-film metal nanowire networks are being pursued as a viable alternative to the expensive and brittle indium tin oxide (ITO) for transparent conductors. For high performance applications, nanowire networks must exhibit high transmittance at low sheet resistance. Previously, we have used complimentary experimental, simulation and theoretical techniques to explore the effects of filler aspect ratio (L/D), orientation, and size-dispersity on the electrical conductivity of three-dimensional rod-networks in bulk polymer nanocomposites. We adapted our 3D simulation approach and analytical percolation model to study the electrical properties of thin-film rod-networks. By fitting our simulation results to experimental results, we determined the average effective contact resistance between silver nanowires. This contact resistance was then used to quantify how the sheet resistance depends on the aspect ratio of the rods and to show that networks made of nanowires with L/D greater than 100 yield sheet resistances lower than the required 100 Ohm/sq. We also report the critical area fraction of rods required to form a percolated network in thin-film networks and provide an analytical expression for the critical area fraction as a function of L/D. [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z6.00002: A simple method to make an electrical connection between ZnO microwire and substrate through nanoscale metal evaporation Hakseong Kim, Jinkyung Lee, Hoyeol Yun, Sang Wook Lee We developed a simple method to make an electrical connection with nanoscale electrodes on microscale wire using suspended Poly(methyl methacrylate) (PMMA) strings. Less than 90 nm height of Ti/Au made a complete electrical connection on the ZnO microwires of which diameter is around 2 $\mu $m. A cross linked PMMA string was bridged between ZnO microwire and substrate for making good electrical connection. The contact resistance of ZnO microwire fabricated by this method was much lower than that of device fabricated by standard E-beam lithography and evaporation. This fabrication method is readily extendible to prepare nano scale electrodes on various micro sized materials and serves as a pathway for studying their mesoscopic transport phenomena. [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z6.00003: High-performance Flexible Photodetectors based on Aligned Cadmium Sulfide Nanowire Networks Dong-Guk Cho, Kwang Heo, Hyungwoo Lee, Yongju Park, Jinho Park, Hyun-Jin Lim, Duhee Yoon, Changhee Lee, Miyoung Kim, Hyeonsik Cheong, Jonghyurk Park, Jikang Jian, Seunghun Hong We developed a method to mass-produce aligned cadmium sulfide (CdS) nanowire (NW) network channels for highly flexible and high-performance photodetectors. In this method, CdS NWs were aligned along the molecular patterns on flexible substrates by a directed assembly strategy. The aligned CdS NW patterns were utilized as the channel of flexible photodetectors. The photodetectors based on \textit{aligned} CdS NWs showed $\sim$ 10 times higher photosensitivity and $\sim$ 100 times faster photoresponse than those based on \textit{randomly-oriented} CdS NW networks. Additionally, the stable photoconductive characteristics of our flexible photodetectors were maintained even when the photodetectors were bent down to a 0.2 mm radius of curvature. This simple but efficient strategy should pave the way for the large-scale fabrication of low-cost and high-performance flexible photodetectors based on the aligned CdS NW networks. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z6.00004: Growth of aligned Mo$_6$S$_6$ nanowires on a Cu(111) Maral Aminpour, Duy Le, Dezheng Sun, Wenhao Lu, Chen Wang, Quan Ma, Ludwig Bartels, Talat S. Rahman We report the possibility of using the Cu(111) surface for growing molybdenum sulfide nanowire (Mo$_{6}$S$_{6})$ based on density functional theory and scanning tunneling microscopy investigations [1]. A small lattice mismatch between the nanowires and strong substrate interactions lead to epitaxial growth of the nanowires at alignment with the substrate crystallographic axes and at a preferred inter-wire separation.\\[4pt] [1] Duy Le, Dezheng Sun, Wenhao Lu, Maral Aminpour, Chen Wang, Quan Ma, Talat S. Rahman, Ludwig Bartels [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z6.00005: Structural Characterization and Transport Properties of GaN nanowires in non-serrated and newly discovered serrated morphologies Zheng Ma, Adam Friedman, Latika Menon We present results on the synthesis, structural characterization and transport properties of single crystal GaN nanowires in two different morphologies (non-serrated and serrated nanowires). The synthesis of these two types of nanowires is carried out in chemical vapor deposition with Au catalysts. Different from the regularly non-serrated GaN nanowires, the GaN nanowires in ``serrated'' morphology have been newly discovered by our group. By controlling the growth conditions, it has been demonstrated that GaN nanowires with regular periodic serrations along the surface of the nanowire can be produced under specific conditions as for large-sized Au catalysts and excess concentration of gallium oxide. Detailed structural and morphological characterization studies reveal interesting features for these two growth modes. In an attempt to understand how these structural and morphological variations impact the electrical properties, transport studies on single GaN nanowires (both serrated and non-serrated) are currently underway. The transport properties, namely current versus voltage will be obtained for such nanowires which in turn will reveal important information on the potential applications of such wires in optoelectronic devices. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z6.00006: On/off-current Ratio and Ambipolar Behavior of Narrow Bandgap III-V Nanowire FETs Yanjie Zhao, Drew Candebat, Collin Delker, Yunlong Zi, David Janes, Joerg Appenzeller, Chen Yang III-V nanowires (NW) are promising candidates for future device applications due to the high bulk mobility. Yet the small bandgap may result in undesirable high off-current. Here we establish a simple but reliable model that quantitatively explains how channel bandgap and Schottky barriers at metal contacts affect the ambipolar characteristics and the achievable on/off-current ratios of NW-FETs. Thus one can gain insights of the expected transfer characteristics of a given channel material with certain device structure, and the optimal choice of materials for different device applications in ultimately scaled cases. The physics of electron transport in both ideal case (no Schottky barrier) and practical case (with Schottky barrier) is studied. The impact of Schottky barriers is evaluated by numerical calculation of the tunneling current, and is found to play a critical role for the different characteristics observed. A universal plot of on/off ratio vs. bandgap is presented. The excellent agreement between our simulation predictions and experiment results from InAs, InSb, Ge NWs and CNTs highlights the potential of our approach for understanding narrow bandgap NW-FETs, bridging material development and device applications, and guiding future transistor design. [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z6.00007: Resistive Switching in Metal-Nanowire/Polymer Nano-Gap Devices Rose M. Mutiso, James K. Kikkawa, Karen I. Winey We recently presented the first examples of reversible resistive switching in bulk, glassy polymer nanocomposites. At compositions near the percolation threshold, Ag nanowire-polystyrene composites exhibit reversible resistive switching upon increase voltage at room temperature. We proposed that switching in these materials is the result of the field-induced formation of Ag filaments that bridge adjacent nanowire clusters, extending the percolation network and decreasing the sample's bulk resistivity. To further understand the switching mechanism and explore possible applications, we have designed and fabricated single-gap nanowire devices comprised of lithographically-defined metal lines separated by polymer-filled nano-gaps. We have successfully demonstrated reversible resistive switching in our nano-gap Ag/PS devices when the gap size is 20 - 100nm, observing highly reversible switching behaviors in some samples with high on/off ratios for over 50 cycles. Preliminary ex-situ high resolution imaging of the devices shows significant gap remodeling after a switching event, implying that the switching mechanism is linked to some form of electromigration of Ag electrodes. Additional ex- and in-situ characterization studies to elucidate observed trends are in progress. [Preview Abstract] |
Friday, March 22, 2013 12:39PM - 12:51PM |
Z6.00008: Nonlocal Response of Plasmonic Nanowire Metamaterials in the ENZ Regime Brian Wells, Anatoly Zayats, Viktor Podolskiy Nanowire metamaterials are a class of materials formed by an array of aligned plasmonic nanowires embedded in a dielectric host which exhibit strongly anisotropic behavior. For a wide range of excitation frequencies, the optical properties of these systems are dominated by two waves with different polarizations. In contrast to this behavior, in the epsilon-near-zero (ENZ) frequency range, excitation of additional wave mode has been observed. In this frequency range the contribution of spatial dispersion becomes increasingly important and a modified dispersion relationship for the anisotropic metamaterials must be used. The properties of the additional wave need to be taken into consideration during design and analysis of the properties of nanowire-based systems$.$ Here we present analytical and computational studies of the nonlocal optical response of plasmonic nanowire metamaterials. Dispersion of photonic modes of plasmonic metamaterials have been studied as a function of wavelength, geometry, and material parameters. A new analytical description of the optical properties of nonlocal nanowire systems has been developed. It is shown that the optical response of the system results from the coupling of conventional effective-medium-dominated oscillations with plasmon-polariton-type oscillations. The presented model is in agreement with numerical solutions of Maxwell's equations. [Preview Abstract] |
Friday, March 22, 2013 12:51PM - 1:03PM |
Z6.00009: ABSTRACT WITHDRAWN |
Friday, March 22, 2013 1:03PM - 1:15PM |
Z6.00010: First-principles study of bio-conjugated ultra-thin silicon nanowires: Interaction with a PNA-RNA double helix Xiaoliang Zhong, William Slough, Ravindra Pandey, Craig Friedrich We present the results of a first-principles study based on density functional theory of peptide nucleic acid (PNA) - ribonucleic acid (RNA) double helix conjugated silicon nanowires (SiNWs). The effects of a hexane linker functionalization, probe PNA strand immobilization, and target RNA strand hybridization on the electronic states of the ultra-thin SiNWs in a dry condition are investigated. All of these effects appear to marginally modify the core silicon states of the nanowires, manifested by a low level of p-doping in SiNWs. The intrinsic energy gap of the SiNWs is essentially unchanged, though there exist mid-gap states contributed by the PNA/RNA molecules which tend to localize near the Fermi energy. Overall, the bio-conjugation considered does not appear to significantly affect the intrinsic electronic and transmission states of the ultra-thin SiNWs. [Preview Abstract] |
Friday, March 22, 2013 1:15PM - 1:27PM |
Z6.00011: Wide bandwidth nanowire electromechanics on insulating substrates at room temperature Abhilash Sebastian, John Mathew, Shamashis Sengupta, Maheshwar Gokhale, Arnab Bhattacharya, Mandar Deshmukh We present a simple fabrication scheme for nano-scale devices on insulating substrates. Doubly clamped InAs nanowire resonators with local gate configuration are fabricated on sapphire substrates. Parasitic capacitance is reduced on insulating substrates thus enabling measurements at all temperatures and particularly above room temperature, an essential requirement for NEMS sensors. Mechanical motion of the nanowire is capacitively actuated and detected using a network analyser. This technique provides wide bandwidth radio frequency transduction and allows the nanowire oscillations to be probed at a much faster rate compared to mixing techniques. Both in-plane and out-of-plane vibrational modes of the nanowire are observed and the non-linear response of the resonators is studied. Quality factor of the resonator increases at low temperatures. We also study the relation between mechanical motion and thermal strains in the nanowire. This opens up a new approach in studying thermal properties of nanostructures. Our method of fabrication can be extended to NEMS devices on flexible substrates and other nanostructures. [Preview Abstract] |
Friday, March 22, 2013 1:27PM - 1:39PM |
Z6.00012: Enhanced Performance in Flexible Binder-free SWCNT Membrane EDLC Danhao Ma, Pralav Shetty, Kofi Adu, Ramakrishnan Rajagopalan We present results on an aqueous symmetric double layer electrochemical capacitor (EDLC) constructed with flexible binder-free single wall carbon (SWCNTs) membrane as electrodes. The capacitors were cycled from 0 to 1V @ 10 A/g for 10,000 cycles with 99.9{\%} coulombic efficiency and 94{\%} energy efficiency, and 100{\%} depth of discharge. The power performance of the aqueous symmetric SWCNTs membrane capacitor is almost 100 --1000 times better than commercial non-aqueous EDLC capacitors. [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 1:51PM |
Z6.00013: Synthesis and HRTEM Electron Diffraction Characterization of Monocrystalline V$_2$O$_5$ Luisa Tafoya, Luis Rendon, Patricia Santiago, Elizabeth Chavira, Ernesto E. Marinero, Vicente Garibay, Leonardo Gonzalez We have synthesized V$_{2}$O$_{5}$ nanorods via solvothermal synthesis. By controlling the synthesis conditions, unidirectional crystalline growth is achieved. HRTEM and XRD studies reveal that the resulting nanorods are monocrystalline and are on average 80 nm in width and readily grow to a few microns in length. Utilizing electron diffraction we investigate the growth of these nanostructures along preferential crystalline planes. XRD confirms also that the crystalline phase of the nanorods is orthorhombic. [Preview Abstract] |
Friday, March 22, 2013 1:51PM - 2:03PM |
Z6.00014: Narrow peaks in the current power spectra of nanomechanical resonators. Dong Liu, Adrian Bachtold, Joel Moser, Alex Levchenko, Mark I. Dykman We show that the power spectrum of current through a nanomechanical resonator has narrow peaks at the frequencies of mechanical modes. These peaks can be selectively downshifted to low frequencies by applying almost resonant ac source-drain or gate voltage. Our analysis refers to the Coulomb blockade regime, where the current is limited by tunneling through the contacts. Where the tunneling rate largely exceeds the vibration frequency, the analysis can be done in terms of the conductance that adiabatically depends on the displacement of the nanoresonator. In a more general case the current power spectrum near the narrow vibration-induced peaks is related to the vertex correction for the corresponding Green function. The spectral peak at low frequency can result also from the vibration nonlinearity in the absence of inversion symmetry. We note that measuring the power spectra of the current noise provides an alternative to the often complicated direct measurements of the absorption spectrum of coupled electron-vibrational systems. [Preview Abstract] |
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