Bulletin of the American Physical Society
Joint Fall 2009 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 54, Number 13
Thursday–Saturday, October 22–24, 2009; San Marcos, Texas
Session C1: Condensed Matter Physics II |
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Chair: Hui Fang, San Houston State University Room: LBJ Student Center 3-9.1 |
Friday, October 23, 2009 2:00PM - 2:12PM |
C1.00001: Magnetic polystyrene-based microbeads for bioassays Marcela L. Redigolo, Gautam Hemani, Stephen Zhou, Diandra L. Leslie-Pelecky Flow cytometry uses fluorescence to detect specific compounds in a sample; however, the number of different wavelengths that can be detected limits the number of analytes that can be identified. We are adding magnetism as an additional parameter to increase the number of analytes that can be simultaneous screened for. We report the synthesis of polystyrene microbeads loaded with exchange-coupled samarium cobalt (SmCo$_{5})$ particles. SmCo$_{5}$ was chosen for its high remanent magnetization, allowing measurement without the need for an applied field. The magnetic-particle-containing polystyrene beads had an average size of 8 $\mu$m. Dispersability in water was enhanced by coating them with the triblock copolymer Pluronic F-127, which also facilitates future functionalization. We will present the synthesis of the microparticles and the effect of synthesis parameters on their magnetic and physical properties. [Preview Abstract] |
Friday, October 23, 2009 2:12PM - 2:24PM |
C1.00002: Thermal Properties of Metallic Nanowires: Modeling {\&} Experiment Nenad Stojanovic, Jordan Berg, Sanjeeva Maithripala, Mark Holtz Effects such as surface and grain boundary scattering significantly influence electrical and thermal properties of nanoscale materials with important practical implications for current and future electronics and photonics. Conventional wisdom for metals holds that thermal transport is predominantly by electrons and transport by phonons is negligible. This assumption is used to justify the use of the Wiedemann-Franz law to infer thermal conductivity based on measurements of electrical resistivity. Recently experiments suggest a breakdown of the Wiedemann-Franz law at the nanoscale. This talk will examine the assumption that thermal transport by phonons can be neglected. The electrical resistivities and thermal conductivities of aluminum nanowires of various sizes are directly measured. These values are used in conjunction with the Boltzmann transport equation to conclude that the Wiedemann-Franz law describes the electronic component of thermal conductivity, but that the phonon term must also be considered. A novel experimental device is described for the direct thermal conductivity measurements. [Preview Abstract] |
Friday, October 23, 2009 2:24PM - 2:36PM |
C1.00003: An investigation of wetting phase evaporation from capillary porous matrices Curtis Lee, Jessica White, Aaron Sansom, Lorne Davis Drying of porous materials is important to a wide variety of applications spanning art, architecture, cooking, agriculture, and engineering. To better understand the phenomenon, we used low-field NMR relaxometry to gain insight into the behavior of air and water within the individual pores during drying. We applied a singular value decomposition algorithm to invert low-field NMR CPMG T$_{2}$ data into apparent pore size distributions and measured the drying rates and the changes in relaxation distributions for alumina matrices of differing pore sizes and for sandstones. We observed two regions of constant drying rate with a large, sharp break in slope when the wetting phase saturation became discontinuous. In both regimes, the surface evaporation rate was controlled by capillary wicking action. Moreover, the drying rate in the early regime was greatly enhanced over evaporation from bulk fluid. The continuous decrease in mean T$_{2}$ of the sample during drying suggests that air penetrates along the pore centers while leaving water wetting the pore walls. [Preview Abstract] |
Friday, October 23, 2009 2:36PM - 2:48PM |
C1.00004: Automation of the Al anodization used for the fabrication of highly ordered sub-100-nm nanopore arrays Jacob Gonzales, Karie Badgley, Igor V. Roshchin The anodization of aluminum films grown on silicon substrates under appropriate conditions is used to fabricate porous alumina arrays. Such porous arrays are used as sensors or lithography masks for fabrication of sub-100-nm nanodot arrays. The self-assembly of these pores into ordered arrays is determined by anodization parameters. We report on the automation of the anodization process that allows us to monitor and control these parameters. To improve ordering, two-step anodization is used. Through real-time current integration, computer software determines the depth of the anodized alumina, which allows us to stop the 1st anodization step. Control of voltage and temperature is also important for controlling pore diameters. Voltage and current are plotted in real time and recorded along with other parameters of sample fabrication. We investigate possibilities to automatically stop the anodization, once the Al film is anodized all the way through, using analysis of the rate of change of the anodization current. Control and optimization of other parameters will be discussed. Funded by Texas A{\&}M University and Texas A{\&}M University -- CONACyT Collaborative Research Grant Program. [Preview Abstract] |
Friday, October 23, 2009 2:48PM - 3:00PM |
C1.00005: Metallic out-diffusion quantification in polymers by x-ray fluorescence Miguel Bencomo, Miguel Castro-Colin X-ray fluorescence is a technique that has sensitivity within parts-per-million elemental content level, which is sufficient to probe trace materials. In this study two X-ray sources were used, copper and silver radiation, to detect metallic additives used to modify the properties of polymers. The technique requires minimal to no sample preparation and is non-destructive. In the present case trace materials of heavy metals are identified in two types of polymers, polypropylene and polycarbonate, before and after being exposed to energy intake sufficient to detach the metals directly or to promote the formation of hydroperoxide; this last one indirectly produces detachment through re-arrangement of the polymeric matrix. Quantification of heavy metal detachment and out-diffusion is relevant due to possible adverse effects that may arise when such elements make contact with consumables. [Preview Abstract] |
Friday, October 23, 2009 3:00PM - 3:12PM |
C1.00006: Zr Doping Effects on LiFePO$_4$ Cathode Materials for Lithium-Ion Batteries Travis Neeley, Jacob Hill, Julio Sanchez-Berlanga, Gan Liang, Hui Fang LiFePO$_4$ cathode materials doped with various percentages of Zr on the Fe site are synthesized using both the solution and ball milling methods. X-ray diffraction, cyclic voltammetry, and constant current charge/discharge measurements are employed to characterize the structural, electronic, and electrochemical properties of the samples. The effects caused by Zr doping on Fe site sintered at various temperatures will be discussed and presented. [Preview Abstract] |
Friday, October 23, 2009 3:12PM - 3:24PM |
C1.00007: Doping Effects of LiFePO4 Cathode Materials for Lithium-Ion Batteries Jacob Hill, Julio Sanchez Berlanga, Travis Neeley, Gan Liang, Hui Fang The effects of doping on Fe site of LiFePO4 cathode materials with varying concentrations of W, synthesized by the solution and ball milling methods, will be presented. X-ray diffraction, cyclic voltammetry, and constant current charge/discharge measurements are employed to characterize the structural, electronic, and electro chemical properties of the samples. The effects of varying reaction temperature and environmental composition will also be analyzed. [Preview Abstract] |
Friday, October 23, 2009 3:24PM - 3:36PM |
C1.00008: Magnetic Thermal Hysteresis in Dy nanolayers Ajani Ross, Ali Koymen, Artur Carrico, Ana Dantas, Robert Camley Magnetic thermal hysteresis is observed when the temperature dependent magnetic properties of a material are reliant on the starting point of the measurement. Samples of pure Dysprosium (Dy) were grown on substrates of glass and sapphire. We observed magnetic thermal hysteresis in these thin film Dy samples at low values of constant external magnetic field strengths. The temperature is swept from 20K to 300K at constant field, then back (300K to 20K) under the same field. In these temperature sweeps differences in magnetic moment were observed near the low end of the temperature range. Experiments are being done, currently, to confirm the existence of alternate helicity (AH-state) and helical (H-state) states in Dy films, which are believed to be the cause of the observed thermal hysteresis. [Preview Abstract] |
Friday, October 23, 2009 3:36PM - 3:48PM |
C1.00009: Synthesis and Characterization of LiFePO$_4$ Cathode with Fe:P Deficiency for Lithium Ion Batteries Hui Fang, Travis Neeley, Jacob Hill, Gan Liang LiFePO$_4$ with Fe:P deficiency has been demonstrated a promising cathode material of lithium ion battery for fast rate, high capacity applications. In this study, LiFePO$_{4}$ with various amount of Fe:P deficiency are synthesized using high energy ball milling and temperature controlled sintering under reduced gas. X-ray diffraction, X-ray absorption, cyclic voltammetry and constant current charge/discharge measurements are employed to characterize the structural and electrochemical properties of the samples. The effects brought by Fe:P deficiency on charger/discharge rate and capacity will be discussed and presented. [Preview Abstract] |
Friday, October 23, 2009 3:48PM - 4:00PM |
C1.00010: The effects of oxidizing agents in non-contact synthesis of porous silicon Lauren Bennett, Joe Velasquez, III, Toni Sauncy A variety of different oxidizing agents have been studied for their ability to aid in the synthesis of porous silicon by noncontact photo-etching in a 40{\%} HF solution. A single substrate, n-type Sb-doped silicon was used as the base material. The single crystal was cleaved into 1cm$^{2}$ pieces, which were then processed with a series of different oxidizing agents. The oxidizing~agents were~selected based upon potential H+ contribution during the etching reaction process. The resulting thin film regions on each sample were characterized using Raman spectroscopy to investigate crystallite size, photoluminescence spectroscopy to confirm light emission from the thin films and surface resistivity, with film thickness determines by spectroscopic ellipsometry measurements. A large range of pore size and structure was achieved, ranging from the nano- to the mesoporous regime. [Preview Abstract] |
Friday, October 23, 2009 4:00PM - 4:12PM |
C1.00011: Spectroscopic Ellipsometry: Multilayer and porous structures Steve Jackson, Ravi Droopad, Toni Sauncy Due to its non-destructive nature, spectroscopic ellipsometry has become commonplace in the semiconductor industry as a widely used thin film characterization technique. This model dependent technique exploits polarization states of light to study the structures and compositions of thin films ranging in thickness from just a few angstroms to several microns. In this study, three multi-layered MBE-grown thin film stacks were characterized over a spectral range of 2.0-5.0eV along with the irregular structures of a series of stain-etched porous silicon thin film layers. By using a novel modeling technique, the pore size and distribution was determined and correlated with surface resistivity and Raman measurements of the same structures. [Preview Abstract] |
Friday, October 23, 2009 4:12PM - 4:24PM |
C1.00012: NMR Studies of Sn clathrates Xiang Zheng, Sergio Rodriguez, Joseph H. Ross, Jr Clathrates are materials with an open cage structure. Because of the low thermal conductivities these materials may be good choices for thermoelectric applications and energy saving devices. Thus they have become important materials for current study. We report $^{71}$Ga NMR experiments on Ba$_{8}$Ga$_{16}$Sn$_{30}$ clathrates, which have particularly low thermal conductivities We will compare different properties of the two types of Ba$_{8}$Ga$_{16}$Sn$_{30}$ clathrates, type-I and type-VIII, which are different in structure. The NMR lineshapes and relaxation times were measured in temperatures between 295K and 4.2K. For a type-I sample, we observe several different peaks with an unexpectedly large range of Knight shift. Also we observe large changes for the relaxation times at low temperature which are not consistent with the Korringa law, the normal behavior for NMR due to conduction electrons. These results are different from what we observe in other clathrates. Thus we tentatively assign these results to rattling type atomic motion, and will compare the data to models for relaxation due to such motion. This research is supported by the Robert A. Welch Foundation. [Preview Abstract] |
Friday, October 23, 2009 4:24PM - 4:36PM |
C1.00013: Magnetoplastic Properties of Thick Films on Nitinol Substrate Amanda Gregory, Martin Sablik, Wilhelmus Geerts, Kyle Smith, Anup Bandyopadhyay, Fernando Landgraf, Marcos de Campos Understanding the magnetic properties of plastically deformed thin films is vital to the development of thin film devices that will undergo unavoidable stressing. We covered polished nitinol substrates with Fe and Fe-Si films up to 1 micron thick and subjected them to stress which was performed both laterally and by bending over cylinders. Under extreme lateral straining the films would inhomogeneously detach from the substrate. In samples that underwent strain via bending there was no observed film detachment. The magnetic remanence decreased when applied parallel to the stress axis and increased when applied perpendicularly. The coercivity of the strained films exhibited marked change only when measured perpendicular to the stress axis, where it was observed to decrease. Modeling calculations show that residual compressive stress dominates the magnetoplastic properties of thin films. [Preview Abstract] |
Friday, October 23, 2009 4:36PM - 4:48PM |
C1.00014: Introduction of Flux Pinning Centers for Use in Nb3Sn Superconducting Wire David Rahmani, Kyle Damborsky, Peter McIntyre, Nathaniel Pogue Powder metallurgy was used to introduce a homogeneously heterogeneous distribution of nanoscale flux pinning centers in Nb rod for future use in Nb3Sn superconducting wire. The pinning centers consisted of Y, Y2O3, W, Cu, Zr, and Ti. Flux pinning centers in superconducting wire would prevent a decrease in critical current density in the presence of a high magnetic field. The blended powders were consolidated using Cold Isostatic Pressing (CIP) at 50000 PSI. The samples were analyzed and found to contain a high concentration of oxygen, which was found to be excessive for use in a superconductor and may have contributed to poor performance in CIP. Due to the high level of oxygen found in commercially available Nb powder, future attempts will require the manufacturing of Nb powder with a low oxygen content. [Preview Abstract] |
Friday, October 23, 2009 4:48PM - 5:00PM |
C1.00015: Quantum Anomalous Hall Effect with Cold Atoms Trapped in a Square Lattice Xiong-Jun Liu, Xin Liu, Congjun Wu, Jairo Sinova Realization of quantum anomalous Hall effect (QAHE) [1] not only has the potential applications through the study of topological phases such as the technologically important topological insulators, but also has great interest from a basic physics point of view. In this work we propose the realization of the QAHE in a square optical lattice which can be generated from available experimental set-ups of double-well lattices with minor modifications [2]. A periodic gauge potential induced by atom-light interaction is introduced to give a Peierls phase for the nearest-neighbor site hopping to break time-reversal symmetry. The quantized anomalous Hall conductivity is investigated by calculating the Chern number as well as the chiral gapless edge states of our system. We study in detail the experimental detection of the edge and bulk states with which one can determine the topological phase transition from usual insulating phase to quantum anomalous Hall phase. Reference: [1] F. D. M. Haldane, Phys. Rev. Lett. 61, 2015 (1988). [2] X. -J. Liu, X. Liu, C. Wu and J. Sinova, submitted to PRL for publication (2009). [Preview Abstract] |
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