TcSUH
Bi-Weekly Seminar
Oxygen Ion Conductivity and Electronic Conductivity in the Bi-Ru-Alkaline Earth Oxides
Date: Friday March 26, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Bismuth-alkaline earth oxides include a rhombohedral solid solution that is a very good oxygen ion conductor perpendicular to the c-axis at relatively low temperatures (1 S cm-1 at 600-700°C). There is complete mutual on-site solubility between Ba, Sr, and Ca. The Bi content ranges from <10 to 30 cation %. The conductivity mechanism, the variation of conductivity and other properties of the oxide with temperature, and the phase relations of this phase will be discussed. The rhombohedral oxide dissolves many materials potentially used as electrodes. We have synthesized a new rhombohedral oxide saturated in Ru. It has the same oxide conductivity as the Ru-free phase. Phase relations in the Bi-Ru-Sr-Ba-O system will be discussed. The rhombohedral phase is in equilibrium with an alkaline earth ruthenate (not ruthenium oxide) under oxidizing conditions. Alternative electrode materials include Bi-Ru pyrochlores.
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Bi-Weekly Seminar
Rutherford Scattering of Identical Ions-A Test of Quantum Mechanics at MeV Energies with Massive Particles
by: Ki B. Ma
Date: Friday February 20, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Elastic Rutherford scattering between positively charged ions is mediated by the repulsive Coulomb potential. Its differential cross section according to classical mechanics comes out to be the same as the exact quantum mechanical result. Its characteristic 1/E2 energy dependence and cosec4(/2) angular dependence have been well established since 1911. Not predicted by Rutherford then, and missed in Goldberger and Watson2 even as late as 1964, these results break down when the scattering ions are identical, and oscillations in the differential cross section as a function of the scattering angle appear instead of the familiar smooth dependence. This behavior is thoroughly discussed in Landau and Liftshiz3 (1965), but the oscillations were summarily declared to vanish “on averaging over even a small range of values of. This oscillatory behavior is a hallmark of quantum mechanical interference. Dictated by the exchange symmetry of the scattering particles and without a classical counterpart, it constitutes a test for the validity of quantum mechanics versus classical mechanics, a test that can be conducted using massive particles at MeV energies, at room temperature. Here, we report preliminary results on the observation of quantum interference in the Rutherford scattering of carbon from carbon at incident energies between 1 and 4 MeV.
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Bi-Weekly Seminar
Interface and Processing Effects on Oxide Thin Film Epitaxy
Date: Friday November 21, 2003
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Understanding the epitaxial mechanisms, interface structures, and processing condition effects has become a technically important issue in oxide thin film epitaxy and device fabrication. We have systematically investigated the effects from strains, substrate surface step terraces, misfit dislocations, and processing partial pressures and temperatures on the epitaxial behavior and physical properties of various as-grown ferroelectric (Ba,Sr)TiO3, ferromagnetic (La,Ca)MnO3, and highly ionic conductive oxide Gd:CeO2 thin films. Many interesting phenomena have been observed in these systems. For instance, misfit edge dislocation spacings in the ferroelectric Ba0.6Sr0.4TiO3 thin films on (001) LaAlO3 can be adjusted by processing oxygen partial pressures. Strain energy in the highly ionic conductive Gd:CeO2 thin films on (001) LaAlO3 can be released by unique directionally aligned nanoparticles. Models of the surface-step-terrace that induce the formations of conservative and non-conservative nano domain boundary structures have been developed to understand the microstructure-property relationships. Details will be presented in the talk.
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Bi-Weekly Seminar
Magnetic Nanowires
by: Dr. Li Sun
Date: Friday November 07, 2003
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Nanoscience and technology as an emerging interdisciplinary research area has caught a lot of attention in recent years. Nanostructured materials exhibit novel properties bulk samples do not possess, however, fabrication of well-controlled nanostructures, understanding physics at the reduced dimensionality and device application of individual nanomaterial still remain challenging. Here we use nanowires as an example to show how magnetic properties of materials can be designed and tuned by nanofabrication. Magnetic shape anisotropy, finite size effects and magnetization switching in these quasi-one dimensional structures has been studied. Manipulation and potential application of individual single elemental and multi-component magnetic nanowires will be discussed.
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Bi-Weekly Seminar
Dielectric Properties of Biological Cell and Protein Suspensions
Date: Friday October 31, 2003
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The charges in live cells can be polarized by an electric field, creating a dipole moment for each cell. As a result, a suspension of live cells in water has an enormous dielectric response at low frequencies, and this response decreases rapidly with increasing frequency. The magnitude of the low-frequency dielectric response has been shown theoretically to correlate with the cell’s membrane potential. Recently, we have been exploring new applications, such as sensors designed to detect biological warfare agents inside sealed containers. Another ongoing study is the dielectric response of tubulin dimers, in an attempt to determine their intrinsic dipole moment. Tubulin is the protein that comprises microtubules -- remarkable structures that form much of the cellular cytoskeleton. In addition, due to their high concentration in neuronal axons, microtubules have been proposed to play a role in information processing. We are investigating several approaches to performing linear and nonlinear dielectric spectroscopy, ranging from simple direct electrode methods to techniques that employ SQUIDs.
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