Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session H1: Condensed Matter |
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Chair: Gus Hart, Brigham Young University Room: Union East, 3rd Floor University |
Saturday, October 18, 2008 10:30AM - 10:54AM |
H1.00001: Electron and Phonon Transport in Thermoelectric Thin Films and Nanostructures Invited Speaker: Clean, high-efficiency energy technologies are likely to involve devices that employ more than one route to energy conversion. For example, adding a thermoelectric generator to a solar cell could improve the efficiency of overall energy production by converting unused thermal energy to electric energy. Though recent years have seen significant advances, the new developments in materials that will allow thermoelectric devices to fully realize their potential for energy conversion remain elusive. Nanoscale engineering of materials, made possible by modern tools for patterning and manipulation of matter at small length scales, has shown early promise and may lead to rapid improvement in thermoelectrics. A fairly wide range of fundamental studies reveal that the electronic, vibrational, and magnetic excitations in such systems can behave much differently than in bulk, equilibrium phases, but some measurements that are particularly important for thermoelectrics remain very challenging for systems such as thin films and nanowires. This talk will briefly introduce the challenges of thermal measurements of small samples and the fascinating physics of such systems, and describe our current work toward identifying potential breakthroughs in thermoelectric materials through direct experimental studies of electronic, vibrational, and magnetic excitations in small structures and novel materials. [Preview Abstract] |
Saturday, October 18, 2008 10:54AM - 11:06AM |
H1.00002: Spatial self-organization and self-alignment of quantum dots and rods by liquid crystals Dennis Gardner, Ivan Smalyukh We study the spatial self-assembly and self-alignment of CdSe quantum dots and rods in dilute liquid crystal (LC) suspensions. Employing the strong non-bleaching fluorescent signals from the quantum particles, we use fluorescent confocal microscopy to image the 3-D spatial location of the quantum particles. We demonstrate that LC defects and structures allow for controlled localization, alignment, and assembly of these quantum particles. Generalizing our studies for various nanoparticles of different compositions may provide new self-assembly-based methods of nanofabrication of metamaterials needed for applications such as cloaking at optical wavelengths, optical circuits, and super lenses. [Preview Abstract] |
Saturday, October 18, 2008 11:06AM - 11:18AM |
H1.00003: Diffraction by Permanent Gratings in Dye-Doped Liquid Crystal Mikail Abbasov, Gene Carlisle Permanent gratings were written in dye-doped and in dye \textit{and} carbon nanotube-doped nematic LC using low laser power without application of an electric field. The diffraction efficiency of the gratings can be modulated with applied ac fields. Cells doped with both dye CNT show greater diffraction than those doped only with dye. In order to gain further understanding of these materials we have obtained Frederiks transition, capacitance and conductivity data. The presence of CNTs has little effect on the Frederiks transition, which occurs $\sim $ 67 mV/$\mu $m. However, the CNT-doped cells exhibit greater capacitance and conductivity over a wide range of ac fields and frequencies, with significant increases beginning at the Frederiks transition. The dielectric data, which support the diffraction data, will be presented along with a grating model. [Preview Abstract] |
Saturday, October 18, 2008 11:18AM - 11:30AM |
H1.00004: Metal-to-Insulator Transition in Vanadium Dioxide Thin Films Felipe Rivera, Art Brown, Robert Davis, Richard Vanfleet Vanadium Dioxide single crystals undergo a structural first-order metal to insulator phase transition at approximately 68 degrees Celsius. This phase transition exhibits a resistivity change of up to 5 orders of magnitude in bulk specimens. We observe this structural phase transition in thin films of vanadium dioxide, however, the phase transition observed exhibits only a 2-3 order of magnitude change. We present our current progress in understanding this phase transition for polycrystalline thin films of vanadium dioxide from the view of individual particles. Particle sizes ranging 50 to 250 nm were studied by means of electron microscopy. The results of these studies, as well as some of the implications that these findings may have in incorporating this material onto electronic devices will be presented. [Preview Abstract] |
Saturday, October 18, 2008 11:30AM - 11:42AM |
H1.00005: $^{1}$H NMR In Hydrogenated Nano-Crystalline Silicon Thin Films Kristin Kiriluk, T. Su, P.C. Taylor, B. Yan, J. Yang, S. Guha Hydrogenated nano-crystalline silicon (nc-Si:H) thin films is a promising material for multi-junction solar cells. We investigated the local hydrogen environments in nano-crystalline silicon thin films by nuclear-magnetic-resonance. At room temperature, $^{1}$H NMR shows a much higher degree of hydrogen clustering than observed in typical a-Si:H, these hydrogen atoms are probably located at the grain boundaries of the nano-crystallites. As the temperature decreases, the $^{1}$H NMR shows a broadening of the lineshape of the nc-Si:H. These results suggest that the local hydrogen order in nc-Si:H is very different from that in a-Si:H, and this local order may be responsible for certain unique optoelectronic properties of nc-Si:H thin films. The dependence of the spin lattice relaxation time on temperature, however, is very similar to that of a-Si:H. This suggests that even though the local hydrogen order may be different, there is still molecular hydrogen present in nc-Si:H that relaxes the bonded hydrogen. [Preview Abstract] |
Saturday, October 18, 2008 11:42AM - 12:06PM |
H1.00006: Effects of Nanostructure Formation in InAs/GaSb Superlattices Invited Speaker: Self-organized semiconductor nanoscale structures (wells, wires and dots), based on the morphological instability of strained molecular beam epitaxial grown films, has been observed in many III-V systems and is of great importance from both a fundamental and technological point of view. In the non-common anion InAs/GaSb (001) superlattices, which has a small strain, unstable growth at a thickness of a few monolayers has been observed to form nanowire structures. In this talk, the results of a structural and optical analysis of nanostructure formation in these superlattices grown with different interfacial bonds will be presented. X-ray diffraction and kinematical modeling showed that the type of interfacial bond and the sign and magnitude of the strain in the superlattice layer are crucial for the spontaneous formation of the nanowires; therefore, with proper design of the interface, self-assembled nanostructures can be grown in material systems with small strain, which would otherwise be impossible. Optical absorption response of nanowire samples were compared to that of planar samples. The optical data suggests that by manipulating the strain state of the superlattices using various interface and buffer layer material, the optical response of the system may be controlled. Control of the nanostructure formation and the properties of the superlattices may lead to improvement in current or the development of new optoelectronic devices. [Preview Abstract] |
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