Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session B31: Insulating Nanostructures |
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Sponsoring Units: DCMP Chair: Babak Nikoobakht, National Institute of Standards and Technology Room: Baltimore Convention Center 328 |
Monday, March 13, 2006 11:15AM - 11:27AM |
B31.00001: Structural and electronic properties of aluminate nanotubes Kee Joo Chang, Yong-Ju Kang Recently, lithium containing aluminate nanotubes have been synthesized by the surfactant templating method. However, their structural and electronic properties have not been clearly understood yet. In this work, using first-principles theoretical calculations, we present a stable tubular structure in the form of AlO$_{2}$, which is energetically stable with fewer strain energies, compared with MoS$_{2}$ nanotubes with similar diameters. All the AlO$_{2}$ nanotubes are metallic with pseudogaps, independent of chilality. For small diameter zigzag tubes, more electron conduction occurs through the outer O shell with longer Al-O bonds, while the whole tube wall contributes to electron conduction for large diameter tubes or armchair tubes, which have similar inner and outer Al-O bond lengths. We find that an AlO tubular form can be stabilized by hole doping. [Preview Abstract] |
Monday, March 13, 2006 11:27AM - 11:39AM |
B31.00002: Formation of SiOx nanoflowers during the VLS growth of silicon nanowires Joonho Bae, Rebecca Thompson-Flagg, Michael Marder, John Ekerdt, Chih-Kang Ken Shih We report the formation of SiOx nanoflowers at the tip of the VLS grown silicon nanowires. The morphology and complexity of the flowers can be reproducibly controlled by varying the growth conditions. ~Structural and compositional analysis of the nanoflowers formed at different stages (from open geometry to close geometry) using TEM and SEM with energy dispersive spectroscopy reveal that the flower results from selective oxidation of silicon at the interface between nanowire and the gold catalyst. ~There is no detectable oxidation in the wire region. The underlying mechanism and the intriguing pattern formation will be discussed. [Preview Abstract] |
Monday, March 13, 2006 11:39AM - 11:51AM |
B31.00003: Ferromagnetism of MnO and Mn3O4 nanowires Myung-Hwa Jung, Jeunghee Park The MnO and Mn3O4 nanowires were grown by thermal evaporation of MnCl2 under the Ar flow. The diameter is in the range 50-100 nm and the length is about 20 ?m. The MnO and Mn3O4 nanowires consist of single-crystalline cubic MnO and tetragonal Mn3O4 crystals, respectively, grown uniformly with the [100] direction. The XPS data suggest that the majority of nanowires could be MnO nanowires. The temperature-dependent FC and ZFC magnetization curves with H=0.1-30 kOe, and the hysteresis curves measured at 5-300 K provide an evidence for the ferromagnetism with TC = 12 K and 43 K, for the MnO and Mn3O4 nanowires, respectively. The hysteresis curves at low temperatures were resolved well by two ferromagnetic components based on Brillouin function form, confirming the ferromagnetism of both MnO and Mn3O4 nanowires. We conclude that the single- crystalline MnO and Mn3O4 nanowires could be excellent ferromagnetic nanomaterials. [Preview Abstract] |
Monday, March 13, 2006 11:51AM - 12:03PM |
B31.00004: Metal-insulator transition in vanadium oxide nanowires Jiang Wei, Zenghui Wang, Yujie Xiong, Younan Xia, David Cobden The oxides of vanadium are strongly correlated electronic materials. In the form of nanostructures, the correlations and the phenomena associated with them should be modified. For instance, in sufficiently thin nanowires the metal-insulator transition, which is first-order in the bulk, should become a crossover. We report on our synthesis of vanadium oxide nanowires and preliminary measurements of their transport properties. The nanowires as grown by vapor phase deposition on SiO$_{2}$ appear to be mainly V$_{2}$O$_{5}$, a semiconductor, and their conductance shows no features as a function of temperature. After annealing in hydrogen, hysteresis is seen in the conductance within a limited temperature range above room temperature, consistent with partial reduction to VO$_{2}$ which undergoes a metal-insulator transition in the bulk at 67$^{o}$ C. After further annealing, the conductance increases by two orders of magnitude and the hysteresis disappears, consistent with further reduction of the nanowires to V$_{2}$O$_{3}$ which is a correlated metal at room temperature. [Preview Abstract] |
Monday, March 13, 2006 12:03PM - 12:15PM |
B31.00005: Magnetoresistive Core-Shell Nanowires Bo Lei, Chao Li, Chongwu Zhou Magnetoresistive La0.67Sr0.33MnO3 nanowires have been synthesized and studied using pulsed laser deposition with MgO nanowires working as the template. Transport studies on these novel nanowires revealed a remarkable metal-insulator transition at 325 k, accompanied by room-temperature colossal magnetoresistance 10 percent under 1 T magnetic field. Furthermore, shape-induced magnetoresistance was observed for magnetic fields applied parallel or perpendicular to the nanowire. In addition, polycrystalline La0.67Sr0.33MnO3 have been obtained by tuning the synthesis condition, leading to a low-field magnetoresistance up to 16 percent at 0.06 T. [Preview Abstract] |
Monday, March 13, 2006 12:15PM - 12:27PM |
B31.00006: Table Salt's New Application in High Throughput Growth of Zinc Oxide Nanowires from Zinc Powder Jian Yang, Wenzhong Wang, Yi Ma, D.Z. Wang, Zhifeng Ren Table salt was found to be very helpful in producing single crystal zinc oxide (ZnO) nanowires in grams quantity with a conversion efficiency of about 60-80{\%}. The growth process involves heating the mixture of zinc powder and table salt at about 600-700ÂșC in flowing gases of oxygen and argon. A conversion efficiency of only 5-10{\%} was achieved when salt was not used. The salt was completely removed by a few times water rinse. The as-grown ZnO nanowires are about 40 -- 100 nm in diameter and 5 -- 10 micrometer in length, and are grown on either zinc oxide particles or on the surfaces of the table salt crystals. Transmission electron microscope studies showed that these ZnO nanowires are highly crystallized single crystals. Photoluminescence spectra of the as-grown and salt-free ZnO nanowires using excitation of 325 nm showed that the ZnO nanowires have a very strong emission in the visible frequency without any emission from the band edge, meaning that surface states dominate the emission. The important role of the salt plays in the high conversion efficiency is discussed. [Preview Abstract] |
Monday, March 13, 2006 12:27PM - 12:39PM |
B31.00007: Growth of Ultra-long Horizontally Grown Zno NWs, their Photoluminescence and Electrical Properties Babak Nikoobakht, Michael Beversluis, Mark Vaudin, Stephan Stranick In this presentation a technique for growth of very long horizontal ZnO NWs on $(11\overline 2 0)$ sapphire surface is discussed, which is a modification to our previously published work (\textbf{\textit{Appl. Phys. Lett.}}\textbf{ 2004, 85(15), 3244)}. This technique provides the in situ alignment, predictable positioning, large scale assembly, diameter control, and production of quantum wires. A crystallographic model explaining the unique growth direction of [1$\mathop 1\limits^-00]$ is proposed, which is supported by electron-back scattering diffraction results. Two photon photoluminescence microscopy of oriented NWs with diameter about 5 nm as well as electrical characterization of individual NWs are discussed. [Preview Abstract] |
Monday, March 13, 2006 12:39PM - 12:51PM |
B31.00008: W$_{3}$O Nanowires as Gas Sensors Sharvil Desai, Biswapriya Deb, Gamini Sumanasekera, Mahendra Sunkara N$_{2}$O interaction on thin films of W$_{3}$O nanowires and nanoparticles at different temperatures and concentrations was investigated. W$_{3}$O nanowire and nanoparticle films were synthesized on quartz substrates by Hot Filament Chemical Vapor Deposition. DC resistance measurements in the Van der Pauw geometrical methods were conducted on the films. It was observed that the W$_{3}$O nanowire thin film as a gas sensor resulted in an improved sensitivity as compared to the W$_{3}$O nanoparticle thin film. Impedance Spectroscopy measurements (1mHz - 100kHz) were also performed in both films to understand the underlying mechanism for these different responses. Measurements on single W$_{3}$O nanowire will also be presented. [Preview Abstract] |
Monday, March 13, 2006 12:51PM - 1:03PM |
B31.00009: Semiconducting Oxide Nanobelt Field Effect Transistors: Characteristics and Applications Yi Cheng, P. Xiong, Lenwood Fields, J.P. Zheng, R. Yang, Z.L. Wang Single-crystalline ZnO and SnO$_{2 }$nanobelts with thickness of 10 -150 nm were synthesized by thermal evaporation of oxide powders without any catalyst. Field-effect transistors have been fabricated based on these oxide nanobelts, using a doped-Si/SiO$_{2}$ substrate. Multi-terminal electrical contacts to individual nanobelts were defined by photolithography, which enabled us to correlate the FET characteristics with the behavior of the contacts. FETs with nonohmic high-resistance contacts showed enhancement mode Schottky barrier FET behavior. In contrast, in devices with low-resistance ohmic contacts, characteristics of an n-channel depletion-mode FET were observed, with ON/OFF ratio as high as 10$^{3}$ (ZnO) and 10$^{5}$ (SnO$_{2})$, and well-defined linear and saturation regimes. Electrical measurements also revealed high transconductance and field-effect mobility for these nanobelt FETs. Effects of surface oxygen adsorption and desorption have been studied by monitoring the transport properties of SnO$_{2}$ nanobelt FET in different gas flow. Importantly, the FET characteristics of the SnO$_{2}$ device showed significant modification by a 2{\%} hydrogen gas flow at room temperature. *This work is supported by NSF NIRT grant ECS-0210332. [Preview Abstract] |
Monday, March 13, 2006 1:03PM - 1:15PM |
B31.00010: Electromechanical Properties of GaN Nanowires Chang-Yong Nam, Papot Jaroenapibal, Douglas Tham, David E. Luzzi, John E. Fischer, Stephane Evoy GaN, an important wide and direct bandgap semiconductor for optoelectronic devices, also possesses excellent thermal stability, chemical inertness, and a high piezoelectric constant, making it suitable for high temperature chemical sensors and transducers. While one-dimensional GaN nanowires have attracted extensive research recently for nano-scale optoelectronic devices, their high aspect ratio, straightness and smooth surfaces suggest potential in nanoelectromechanical system (NEMS) applications such as high sensitivity mass sensing. In spite of such importance, electromechanical properties of GaN nanowires have not been accessed so far. Here, we investigate Young's modulus $E$ and resonance quality $Q$ of GaN nanowires by \textit{in-situ} detection of electromechanical resonances in a transmission electron microscope. For the largest nanowire diameter observed (84 nm), $E$ is close to the theoretical value of bulk GaN ($\sim $300 GPa) and gradually decreases for smaller diameters. Also we find $Q$ generally higher than that of conventionally micromachined nano-scale Si resonators despite the larger surface-to-volume ratio, implying significant advantage of GaN nanowires in NEMS applications. Most nanowires display two closely-spaced resonances, which we attribute to low-symmetry triangular cross-sections. [Preview Abstract] |
Monday, March 13, 2006 1:15PM - 1:27PM |
B31.00011: Electronic and Transport Characteristics of Two-Phase Coaxial Gallium Nitride Nanowires V.M. Ayres, B.W. Jacobs, M.A. Crimp, R.E. Stallcup, A. Hartman, M.A. Tupta, J.B. Halpern, M.Q. He We will present results of investigations of electronic and transport characteristics of two-phase coaxial gallium nitride nanowires. The$\sim $50-100 nm gallium nitride nanowires grown in a direct reaction of metal gallium vapor with flowing ammonia at 850-900\r{ }C without a catalyst have a two phase coaxial zinc-blende/wurtzite structure, shown by high resolution TEM and nanodiffraction experiments. The electronic characteristics were investigated by STM. The transport characteristics were investigated in 2-point and 4-point probe configurations using a Keithley-Zyvex KZ100 Nanoprobing System, in which specially sharpened $\sim $30 nm radius tungsten nanoprobes were coupled to an ultra low noise semiconductor characterization system. The transport experiments were performed under direct SEM observation. Results indicating coaxial transport with different transport characteristics will be presented. [Preview Abstract] |
Monday, March 13, 2006 1:27PM - 1:39PM |
B31.00012: In-situ STM-TEM Studies of Individual GaN Nanowires Mitra Taheri, Blake Simpkins, Pehr Pehrsson, Rhonda Stroud The electronic and structural properties of individual GaN nanowires were studied using a scanning tunneling microscopy (STM) stage that operates inside a high-resolution transmission electron microscope (TEM) allowing simultaneous evaluation of electrical, compositional, and structural properties with nm-scale resolution. The GaN nanowires were prepared by atmospheric CVD on SiO$_{2}$/Si substrates. Catalyst metal deposition consisted of electron-beam lithography patterned Ni dots, enabling diameter- and position-controlled nanowire growth for device-compatible processing. A focused ion beam- scanning electron microscope with an in situ micromanipulator was used to extract single GaN nanowires from the substrate and attach them to copper TEM supports. Analysis of I-V characteristics of individual wires, and any correlation with microstructure, such as wire dimensions, growth habit and defect concentration will be presented. [Preview Abstract] |
Monday, March 13, 2006 1:39PM - 1:51PM |
B31.00013: Spatially Resolved Luminescence from CdSe Nanowires Yong-Joo Doh, Kristin N. Maher, Lian Ouyang, Jiwoong Park, Hongkun Park We report photoluminescence (PL) and electroluminescence (EL) from devices incorporating single cadmium selenide (CdSe) nanowires. Electrical measurements and spatially resolved optical measurements are carried out simultaneously at room temperature, and under constant uniform illumination ($\lambda$ = 480 nm). At low bias voltages ($V$), photoluminescence is observed along the length of the wire, with a spectral peak at 706 nm. Once $V$ exceeds $\pm {1}$V, the PL intensity begins to decrease, and above $V = \pm {2.5}$V localized emission can be seen at one of the contacts (at the positively biased electrode). The EL spectrum shows a peak that is broadened and blue-shifted in comparison to the PL. A mechanism for the observed light emission will be discussed. [Preview Abstract] |
Monday, March 13, 2006 1:51PM - 2:03PM |
B31.00014: Compositional and magnetic ordering in Mo$_{6}$S$_{9-x}$I$_{x}$ nanowires Teng Yang, Shinya Okano, David Tomanek We investigate the effect of atomic ordering and geometry on the relative stability and electronic as well as magnetic structure of Mo$_{6}$S$_{9-x}$I$_{x}$ nanowires using {\em ab initio} Spin Density Functional calculations. The skeleton of these unusually stable nanowires consists of Mo octahedra, which are decorated with S and I atoms and connected by sulfur bridges. These sulfur bridges turn out to be bi-stable, providing the nanowires with the unusual capability to stretch by 20\% at no energy cost. Depending on the degree the nanowires have been stretched, they may reversibly acquire or lose their magnetic moment. The ordering of the decorating atoms, observed in these nanowires, reflects our finding that the total energy depends sensitively on the atomic arrangement at a given stoichiometry. [Preview Abstract] |
Monday, March 13, 2006 2:03PM - 2:15PM |
B31.00015: Dielectric properties and band gap determination of individual nanostructures via valence electron energy loss spectroscopy Shaul Aloni, David Okawa, Michael Johnson, Michael Rousseas, Alex Zettl Recent developments in electron energy loss spectroscopy allow us to measure the dielectric properties near the band gap of the material with resolution better then 0.2 eV. The energy loss spectra in the 0-50 eV range carries information about the dielectric properties of the nanostructures providing information about the plasmon excitations and allows accurate bandgap determination of individual nanostructures. [Preview Abstract] |
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