Bulletin of the American Physical Society
2007 Joint Fall Meeting of the Texas Sections of the APS and AAPT; Zone 13 of SPS
Volume 52, Number 16
Thursday–Saturday, October 18–20, 2007; College Station, Texas
Session F2: CM3: Condensed Matter |
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Chair: Michael Weimer, Texas A&M University Room: Rudder Tower 510 |
Friday, October 19, 2007 3:30PM - 3:42PM |
F2.00001: Correlation between Morphology and Defect Luminescence in Precipitated ZnO Nanorod Powders Michael Cleveland, J. Antonio Paramo, Raul Peters, Yuri M. Strzhemechny, Zorica Crnjak Orel We studied ZnO nanosize rod-shaped structures grown by precipitation. Different growth times were employed. We established a direct correlation between the morphology of the particles and their defect emission. Short growth times (30 min.) yielded irregularly shaped particles with insignificant morphological anisotropy. Such samples revealed relatively weak band gap emission, indicating lower quality of the crystal, and a significant deep defect luminescence centered around 2.2 eV and a relatively shallow defect emission peaking at 3.1 eV. Longer growth times (4 hrs. and 24 hrs.) lead to formation of long nanorods with well-defined hexagonal symmetry. These crystals exhibited reduced defect emission indicating significant improvements in crystal quality. [Preview Abstract] |
Friday, October 19, 2007 3:42PM - 3:54PM |
F2.00002: Crystallite structure of diamond-silicon carbide composites as a function of sintering temperature Stephen Nauyoks, L. Balogh, T.W. Zerda Because diamonds possess many key physical properties, e.g. high hardness and wear resistivity, they are often used in industrial applications. Diamond powder could be sintered with a binding phase to form large volume diamond composites. These diamond composites have a very high hardness and wear resistance, but have relatively low fracture toughness. It has been shown that the use of nano-diamonds in composites has greatly increased the fracture toughness with a minimal decrease in hardness. Silicon-carbide has a high fracture toughness and is often used as a binding phase in diamond composites. Nano-size diamond-SiC composites were sintered under high pressure, high temperature conditions. The crystallite size, stacking fault probability, and dislocation density were determined from x-ray diffraction profiles. It was found that crystallite size increases; while dislocation density and stacking fault probability decreased as sintering temperature increased. These results were confirmed with high resolution TEM images. [Preview Abstract] |
Friday, October 19, 2007 3:54PM - 4:06PM |
F2.00003: Synthesis of LaF$_{3}$:Ce$^{3+}$ Nanoparticles With Tunable Emissions Mingzhen Yao, Wei Chen Lanthanide based nanoparticles have a good potential as a new kind of luminescent materials. In this presentation, we report the synthesis of Cerium-doped LaF$_{3}$ nanoparticles in dimethyl sulfoxide (DMSO) using chemical reaction at different temperature. The samples prepared at low temperature have a similar emission as the samples prepared in water. However, at high temperatures around 180$^{o}$C, the emission wavelength shifts with the reaction time, from 490 nm to 650nm. The formation of LaF$_{3}$:Ce$^{3+}$ nanoparticles have been identified by X-ray diffraction (XRD) and transmission electron microscopy(TEM). The TEM results show that the average sizes of these nanoparticles are from 10 nm to 13 nm. The mechanisms for the tunable emissions are being investigated. [Preview Abstract] |
Friday, October 19, 2007 4:06PM - 4:18PM |
F2.00004: RF Plasma Torch System for Metal Matrix Composite Production in Nuclear Fuel Cladding Eddie Holik III For the first time in 30 years, plans are afoot to build new fission power plants in the US. It is timely to develop technology that could improve the safety and efficiency of new reactors. A program of development for advanced fuel cycles and Generation IV reactors is underway. The path to greater efficiency is to increase the core operating temperature. That places particular challenges to the cladding tubes that contain the fission fuel. A promising material for this purpose is a metal matrix composite (MMC) in which ceramic fibers are bonded within a high-strength steel matrix, much like fiberglass. Current MMC technology lacks the ability to effectively bond traditional high-temperature alloys to ceramic strands. The purpose of this project is to design an rf plasma torch system to use titanium as a buffer between the ceramic fibers and the refractory outer material. The design and methods of using an rf plasma torch to produce a non-equilibrium phase reaction to bond together the MMC will be discussed. The effects of having a long lived fuel cladding in the design of future reactors will also be discussed. [Preview Abstract] |
Friday, October 19, 2007 4:18PM - 4:30PM |
F2.00005: Extraction of quantum dot size from real time RHEED intensity profiles. C. Rajapaksha, A. Freundlich Semiconductor quantum dots (QDs) have attracted much attention over the past decade due to their potential applications in nano-scale devices. Thus for the performance of many of those devices determination of structural properties of QDs during growth is highly desirable. Reflection high energy electron diffraction (RHEED) is a powerful technique that can be applied to provide in situ real-time structure evolution during thin film growth in high vacuum epitaxial deposition techniques like molecular beam epitaxy. Although it has been shown that the average facet orientation and QD coverage density could be extracted real time from the evolution of RHEED patterns, to date no study was able to provide a method to extract size of QDs during growth. Recently our group, using an analysis based on the kinematical diffraction theory, has predicted that QD heights can be directly extracted from predicted intensity fringes along the chevron tails. In this study RHEED patterns of uncapped faceted self assembled InAs Stranski-Krastanov quantum dots fabricated on GaAs (001) substrate are investigated both theoretically and experimentally. We report the experimental evidence on the existence of these periodic RHEED intensity fringes along chevron tails and demonstrate the possibility of real time assessment of dot size during the growth of self assembled QDs. [Preview Abstract] |
Friday, October 19, 2007 4:30PM - 4:42PM |
F2.00006: Synchrotron based measurements of the photoelectron spectrum of CdTe nanoparticles Aale Naqvi, S. Hulbert, R. Sundaramoorthy, W. Chen, A.H. Weiss Nanoparticle solutions of CdTe of size 540, 585, 656nm, and Au were deposited on silicon substrates of approximately 1cm x 1 cm after etching the substrate with HF. The samples were exposed to soft x-rays of varying energy under ultra high vacuum, $\sim$10$^{-10}$ torr using beam line U16B at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab. The mechanism of the NSLS storage rings---VUV and X-ray---and the design of the beam are described. We performed Auger electron spectroscopy measurements on the samples and identified the peaks through spectroscopic analysis and monitored the damage of the nanoparticles by observing their fluorescence by gradually increasing the photon energy. The nanoparticles were observed to exhibit a time dependent damage response. Future studies aimed at exploring the potential use of nanoparticles as radiation sensitizing agents for cancer treatment are proposed. [Preview Abstract] |
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