Bulletin of the American Physical Society
2005 TSAPS/AAPT/SPS Joint Fall Meeting
Thursday–Saturday, October 20–22, 2005; Houston, TX
Session B4: Nanotechnology |
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Room: Waldorf Astoria C 210C |
Friday, October 21, 2005 2:00PM - 2:12PM |
B4.00001: Crystallography of metallic nanowires fabricated by hydraulic pressure injection Zhiping Luo Metallic nanowires have exhibited enhanced mechanical and physical properties over the bulk samples. In order to link the fabrication process and their properties, knowledge of the crystallography of the nanowires is essential. In this work, by means of transmission electron microscopy (TEM) techniques, crystallographic studies have been performed on the metallic tin (Sn) and bismuth (Bi) nanowires prepared by hydraulic pressure injection method. These wires have size range from 15 - 60 nm in average diameter and up to 10 $\mu $m in length. Electron diffraction experiment showed that most of these wires are single crystals, with preferred crystallographic growing directions. The Sn nanowires were found to have body-centered tetragonal (bct) structure, and their lengths were predominantly along its $<$100$>$ direction. On the other hand, the Bi had a rhombohedral structure, which was slightly distorted from a face-centric cubic structure along the $<$111$>$ direction. Interestingly, the Bi nanowires grew not along its rhombohedral axis but along its pseudo cubic axis directions. Possible growth mechanisms will be discussed. [Preview Abstract] |
Friday, October 21, 2005 2:12PM - 2:24PM |
B4.00002: Investigation of Giant Magnetoresistance in thin Ni-Cu-NiFe Structures C.D. Stehno, W.J. Yeh During the summer of 2005, the REU program at the University of Idaho investigated the phenomenon of Giant Magnetoresistance (GMR) in Nickel/Copper/Nickel-Iron structures. Layer thicknesses were on the order of 10s of nanometers. The three-layer structures were deposited on silicone wafers by means of a magnetron-plasma sputtering system. The sputtering rate of the copper on silicon was determined to be 0.112 nm/sec at 50W and 90mm. Deposit thicknesses was measured with an elipsometer. Seven samples of varying thicknesses were made during the course of the program which yielded GMR changes between 0.15\% and 1.3\% with a Co 10nm, Cu 8nm, and CoFe 30nm structure. [Preview Abstract] |
Friday, October 21, 2005 2:24PM - 2:36PM |
B4.00003: HgSe Semiconductor Nanoclusters in Zeolite A.M. Milinda Abeykoon, E.A. Anokhina, Miguel Castro-Colin, Simon C. Moss, A.J. Jacobson, W. Donner Changing the size of small (10-50 A) nanoclusters of semi-conductors modifies their optical, electronic, magnetic, thermodynamic, and photocatalytic properties. Therefore there are variety of potential electronic, photochemical and non-linear optical applications of these nanoclusters in the industry. Studying the atomic structures of these nanoclusters is necessary for an analysis of the transition from molecular to bulk semi-conductor properties. Our primary challenge has been to produce HgSe semiconductor nanoclusters with a precise, controllable and narrow size distribution. Since a zeolite framework constrains the size and shape of species encapsulated within a pore, we use zeolite pores to contain our nanoclusters. AXS (Anomalous X-ray Scattering) technique is used in combination with the PDF (atomic pair distribution function) technique to solve for the structure of the nanocluster. We use optical absorption measurements to determine the band gap of the cluster. Finally we intend to perform Raman Spectroscopy to complement our determination of local structure and to probe the electronic properties of the semiconductor nanoclusters. [Preview Abstract] |
Friday, October 21, 2005 2:36PM - 2:48PM |
B4.00004: A Vibrating String Model to Explain Microwave Heating of Carbon Nanotubes James Roberts, Zhou Ye, Bill Deering, Krokhin Arkady Heating of carbon nanotubes (CNTs) by microwaves is described in terms of nonlinear dynamics of a vibrating nanotube. Results from the model provide a way to understand several observations that have been made. It is shown that transverse vibrations of CNTs during irradiation can be attributed to parametric resonance, as occurs in the analysis of Melde's experiment on forced longitudinal vibrations of a stretched elastic string. For many kinds of carbon nanotubes (SWNT, DWNT, MWNT, ropes and strands) the resonant parameters are found to be located in an unstable range of the parameter space of Mathieu's equation. Third degree wave equations are used to qualitatively describe the effects of phonon-phonon interactions and energy transfer from microwaves to CNTs. This result provides a way to input energy from microwaves to carbon nanotubes besides the usual Joule heating via electron-phonon interaction. This paper appears to be the first to point out the role of nonlinear dynamics in the heating of CNTs by microwaves [Preview Abstract] |
Friday, October 21, 2005 2:48PM - 3:00PM |
B4.00005: Negative static dielectric constant in a nano-colloid Jason Shulman, Feng Chen, Stephen Tsui, Yuyi Xue, C.W. Chu We have observed a negative dielectric constant ($\varepsilon'$), at low frequencies, in colloids consisting of urea coated Ba$_{0.8}$Rb$_{0.4}$TiO(C$_{2}$O$_{4})_{2}$ nanoparticles suspended in silicone oil. The dielectric constant has been shown to possess a plasma-like dispersion, which suggests that the static $\varepsilon'$ retains the negative sign. Numerous studies have previously reported negative capacitances. While explanations vary, most of the reports attribute the effect to electrochemical reactions and delayed release of carriers. Our results indicate that these cannot be the origin of the negative dielectric constant observed in the colloid. Additionally, a sign change has been observed in the off-phase currents, which is consistent with the sign change of $\varepsilon'$. [Preview Abstract] |
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