Bulletin of the American Physical Society
Joint Fall 2011 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 56, Number 7
Thursday–Saturday, October 6–8, 2011; Commerce, Texas
Session D4: Nanoscience I |
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Chair: Suresh Sharma, University of Texas at Arlington Room: Sam Rayburn Center Second Floor, Room Vision |
Friday, October 7, 2011 1:40PM - 1:52PM |
D4.00001: Benchmarks and applications of novel density functionals to semiconducting polymers Benjamin Janesko Semiconducting polymers show substantial promise as the active ingredients in inexpensive, flexible, processable ``plastic electronics'' and ``plastic solar cells.'' The difficulty and expense of polymer synthesis makes computational prescreening of novel polymer candidates essential for guiding experiment. Density functional theory (DFT), particularly using hybrid exchange-correlation functionals, has been broadly applied to modeling isolated polymer chains. However, these functionals can be formally and computationally problematic for bulk polymers associating via noncovalent interactions. Screened hybrid and ``Rung 3.5'' density functionals, particuarly their dispersion-corrected variants, show promise for ameliorating these limitations. This work presents benchmarks of these new functionals for this problem, and applications to novel conjugated and nonconjugated semiconducting polymers. [Preview Abstract] |
Friday, October 7, 2011 1:52PM - 2:04PM |
D4.00002: Gold/Copper Sulphide core/shell nanoparticles for Photothermal Therapy Santana Bala Lakshmanan, Xiaoju Zou, Wei Chen One of the biggest successes in photothermal therapy (PTT) is the use of gold (Au) nanoparticles. But its disadvantage is that it is too expensive and in addition the NIR absorption in gold nanostructures is from surface plasmon resonance which is dependent on the dielectric constant of the surrounding matrix. Thus the plasmon absorption maxima would shift for in-vivo observations compared to in-vitro. Alternatively, Copper sulphide (CuS) nanoparticles, developed recently, have also been used for PTT. Their advantage over gold nanostructures is that they have NIR absorption around 1100 nm which originates from the d-d transition of Cu2+ ions unlike surface plasmon resonance in gold nanostructures. Therefore, in this paper, we combined the above two nanoparticle systems and developed a new type of agent -Gold/Copper Sulphide (Au/CuS) core/shell nanostructure that has better photothermal conversion efficiency and also overcomes the limitations of the existing nanoparticle systems for PTT. The TEM results confirmed the core/shell structure of Au/CuS nanostructures. From UV-Vis-NIR spectrometer we obtained that these core/shell nanostructures have maximum absorbance at 1100 nm and absorption intensity much higher than only Au and only CuS nanoparticles systems. This, in turn attributed to the relatively high photothermal conversion efficiency of Au/CuS nanostructures. [Preview Abstract] |
Friday, October 7, 2011 2:04PM - 2:16PM |
D4.00003: Gas sensing properties and role of oxygen vacancies in Indium Oxide nanowires Pradeep Gali, Fang Ling Kuo, Gopal Sapkota, Prathyusha Nukala, Nigel Sheperd, Usha Philipose We report on the effect of oxygen vacancies on defect related emission and the electronic properties of In$_{2}$O$_{3}$ nanowires, synthesized by vapor phase transport. The as-grown nanowires connected in an FET type of configuration shows n-type conductivity, which is ascribed to the presence of oxygen vacancies in the nanowire. The resistivity, transconductance, field effect mobility and carrier concentration of the In$_{2}$O$_{3}$ nanowires were determined to be 1.82 x10$^{-2 }\Omega $cm, 11.2 nS, 119 cm$^{2}$V$^{-1}$s$^{-1}$ and 4.89 x 10$^{17}$cm$^{-3}$ respectively. The presence of oxygen vacancies was also confirmed by photoluminescence measurements, which show a strong U.V emission peak at 3.18 eV and defect peaks in the visible region at 2.85 eV, 2.66 eV and 2.5 eV. We present a technique of post-growth annealing in O$_{2}$ environment and passivation with (NH$_{4})_{2}$S to reduce the defect induced emission. A single In$_{2}$O$_{3}$ nanowire with ohmic contacts was found to be sensitive to gas molecules adsorbed on its surface. [Preview Abstract] |
Friday, October 7, 2011 2:16PM - 2:28PM |
D4.00004: A Study of point defects and cause of nonstoichiometry in InSb nanowires Gopal Sapkota, Usha Philipose On account of its direct, narrow band gap (0.18 eV at 300 K) and very high electron mobility (7.8 m$^{2}$V$^{-1}$S$^{-1})$, Indium Antimonide (InSb) is a promising material for device applications. Synthesizing crystalline InSb as a low dimensional system would lead to the realization of nanoscale devices like IR photodetectors. However, its synthesis remains a challenge because its stoichiometry is found to be critically dependant on growth conditions. In this talk, we present a study of the influence of growth parameters such as temperature and vapor pressure of constituents on the morphology and stoichiometry of InSb nanowires. Transport measurements on nanowires show strong n-type conduction attributed to a large number of electrically active impurities -- Sb vacancies. We present a simple thermodynamic model to qualitatively explain our experimental findings of the evidence of point defects in these nanowires. Indium and antimony vacancies and charged versions of these defects are determined as a function of temperature and partial pressure of antimony. [Preview Abstract] |
Friday, October 7, 2011 2:28PM - 2:40PM |
D4.00005: Studies of Porosity, Connectivity, and Parasitic Phases in Textured Bi-2212/Ag after Non-Melt Sintering. Feng Lu, Kyle Damborsky, Peter McIntyre, Al McInturff, Nathaniel Pogue, Klaus Smit High-angle grain boundaries (HAGBs) result in weak links that limit current transport in high temperature superconductors. The powder filling in commercially available Bi-2212 round wires has random orientation of the grains, and as a result HAGBs are formed during the partial-melt processing. We have developed an alternative method in which Bi-2212 fine powder is roll-processed to produce a continuous ribbon with a high degree of texture. In this study textured Bi-2212 pellets were subjected to sintering to investigate the impact of sintering on texture, density, connectivity, and microstructure. A regime of non-melt sintering parameters were identified which produce near-solid density, improved texture, extensive growth of the Bi-2212 phase, and no significant growth of parasitic phases. We are now applying the process to develop continuous ribbons of textured Bi-2212/Ag green wire in our ``Textured Powder Jelly-Roll'' process. [Preview Abstract] |
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