Bulletin of the American Physical Society
2005 72nd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 10–12, 2005; Gainesville, FL
Session EE: Poster Session II |
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Room: Hilton Cypress |
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EE.00001: Classical MD Simulation Study of Silica Glass Chao Cao, Krishna Muralidharan, Grace Greenlee, Haiping Cheng The structure and mechanical properties of silica glass is studied using classical MD simulation, which uses BKS potential. Different behaviors for bulk glass and nano-wire glass were observed, and the underlying mechanism was analyzed. This study shows that 2-membered rings play an important role in the mechanical behavior of silica glass. [Preview Abstract] |
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EE.00002: From clusters to bulk systems: Water-silica interactions Yao He, Chao Cao, Yin-Xia Wan, Hai-Ping Cheng We present our computational investigations on the energetics of clusters that consist of H$_{2}$O and SiO$_{2}$ using first-principles Born-Oppenheimer molecular dynamics method. Cohesive energy and hydration energy of both pure (or dry) and hydroxylated (or wet) ring-structured clusters have been investigated as functions of system size. We have found clear trends of energy as the cluster size increases. Energetics of a small silica nano-rod that contains 108 atoms is also obtained as a middle reference point for size evolution. Results from cluster and nano-rod calculations are compared with values from bulk quartz and cristobalite calculations using various theoretical treatments. [Preview Abstract] |
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EE.00003: Hole Spin Relaxation in Diluted Magnetic Semiconductors Yongke Sun, Gary Sanders, Fedir Kyrychenko, Christopher Stanton We used a generalized Pidgeon-Brown model which incorporates the finite $k_{z}$ effects and includes the exchange interaction to calculate the band structure of bulk GaAs and GaMnAs. In Fermi's golden rule approximation, the hole spin relaxation in both bulk GaAs and GaMnAs have been studied. Quantitative calculations show that in intrinsic bulk GaAs, the hole spin life time is around $110$ fs, which is due to phonon scattering. However, in GaMnAs, $p-d$ exchange interaction and high density of impurities provide the other spin flip scattering channels and dominate. The nonequilibrium spin relaxation time is around several fs. [Preview Abstract] |
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EE.00004: Observation of butterfly hysteresis loops in Ru dimer with large zero-field splitting Chris Ramsey, F.A. Cotton, Wolfgang Wernsdorfer, Irinel Chiorescu, Naresh Dalal We present the magnetic characterization of a metal-metal bonded [Ru$_{2}$]$^{5+ }$dimer with S = 3/2 and a large zero-field splitting of +114 K. This large splitting yields an approximately isolated S = $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ state at low temperature. Field sweep rate dependent hysteresis loops yield unusual butterfly hysteresis loops which pass through a minimum with increasing field strength. This is attributed to a large phonon bottleneck effect. [Preview Abstract] |
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EE.00005: Pulsed field magnetization measurements in an antiferromagnetic Cu(2+) isosceles triangle Chris Ramsey, Ashley Stowe, Kwang-Yong Choi, Yasuhiro H. Matsuda, Hiroyuki Nojiri, Ulrich Korlz, Naresh Dalal EPR and pulsed field magnetization experiments have been carried out on Na$_{9}$[Cu$_{3}$Na$_{3}$(H$_{2}$O)$_{9}(\alpha $-AsW$_{9}$O$_{33})_{2}$]$\cdot $26 H$_{2}$O, an antiferromagnetic isosceles triangle of Cu(2+) ions, in order to examine the quantum phenomena present in a simple spin-frustrated system. Remarkably, the hysteresis loops are characterized by half magnetization steps and asymmetry between positive and negative fields. The EPR determined energy levels suggest that the mixing of the trimer spin-states via antisymmmetric exchange interactions is a factor which induces quantum tunneling in the system. [Preview Abstract] |
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EE.00006: Properties of (Ba$_{x}$Sr$_{1-x})$FeO$_{3}$ thin films and multilayers Charlee Callender, David Norton, Arthur Hebard, Josh Kelly, Ritesh Das (Ba$_{x}$Sr$_{1-x})$FeO$_{3}$ is an interesting perovskite solid solution. SrFeO$_{3}$ is antiferromagnetic, while BaFeO$_{3}$ is ferromagnetic with a Curie temperature of 160 K. The primary effect of Sr substitution into BaFeO$_{3}$ is a decrease in lattice parameter with no change in formal valence. Yet, the transport and magnetic properties of the two end compounds are significantly different. In this project, we are investigating the properties of the (Ba,Sr)FeO$_{3}$ epitaxial thin films and multilayers. The (Ba$_{x}$Sr$_{1-x})$FeO$_{3}$ films were grown via pulsed laser deposition. The films were characterized by X-ray diffraction, Superconducting Quantum Interference Device (SQUID) magnetometry, and atomic force microscopy. [Preview Abstract] |
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EE.00007: Performance of Small and Medium Split Valence Basis Sets in the Calculation of Hydrogen Bonding Properties with DFT Methods Kevin Riley, Kenneth Merz As the speed of modern computers increases while their cost decreases it becomes possible to consider the use of ab initio methods to calculate properties of very large molecules. These types of calculations promise to greatly enhance our understanding of the structure and function of large molecular systems. It seems that the first step to take in making calculations on very large systems would be to use a relatively inexpensive method along with small and medium basis sets such as 3-21G*, 6-31G*, etc. The least computationally expensive ab initio methods are the density functional theory (DFT) methods. One concern that one might have regarding this approach is that the accuracy of DFT methods along with smaller basis sets in describing intermolecular interactions is not very well characterized. In this study we calculate the binding energies and hydrogen bond distances for a set of three hydrogen bonded systems, (H$_{2}$O)$_{2}$, (NH$_{3})_{2}$, and H$_{2}$O-NH$_{3}$ along with several density functionals and basis sets. The functionals used in this study represent each of the five categories (LSDA, GGA, meta-GGA, hybrid, and meta-hybrid) of functionals. The basis sets used here are 3-21G*, 3-21+G*, 6-31G*, 6-31+G*, and 6-31++G*. [Preview Abstract] |
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EE.00008: Ultrasound Attenuation in Liquid $^{3}$He/High Porosity Aerogel H.C. Choi, N. Masuhara, J.-H. Park, M.W. Meisel, Y. Lee, N. Mulders High porosity silica aerogels have been extensively used to study the influence of disorder in p-wave superfluid $^{3}$He. Experimental investigations performed during the last decade revealed three distinct superfluid phases in liquid $^{3}$He /98{\%} aerogel system. The three phases found in this system are called as A, B, and A$_{1}$-like phases (using the same nomenclature as in the bulk), although only the spin component of the order parameter has been studied and found to resemble that of corresponding bulk phases. A complete understanding of the microscopic structure of the p-wave superfluid phases requires identification of both orbital and spin components of the order parameter. Until now, there is no experimental attempt to directly probe the orbital structure in $^{3}$He/aerogel system. To resolve this issue, we performed acoustic measurements by direct transmission of ultrasound through the $^{3}$He/98{\%} aerogel sample. We will present and discuss our preliminary results. [Preview Abstract] |
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EE.00009: Cold Atoms in three-dimensional Confinement formed by Gravity and Atomic Mirrors Alice Quan, Daniel Erenso, Reeta Vyas We have presented a theoretical study of three dimensional matter-wave cavity made of atomic mirrors operating with low intensity evanescent waves with gravity playing a central role in keeping a stable trajectory for cold atoms inside the cavity. The cavity consists of a vertical cylindrical atomic mirror providing a radial confinement with a plane atomic mirror at the bottom and gravity at the top providing the vertical confinement. We have studied cold atoms in such cavity where the dynamics is controlled by gravity. We determine exact energy eigenfunctions (cavity modes) and the distribution of the corresponding energy levels in such kind of confinement for the center of mass motion. Then we studied the overlap of the cavity modes with a condensate described by a three dimensional Gaussian function. A comparison of the exact quantum result with a classical result is also presented. [Preview Abstract] |
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EE.00010: Production and Storage of H$_{3}^{+}$ in an RF Ion Trap. L. Reynolds, S. Brewer, J. Gleeson, B. Myer, R. Stamilio, A. Daw, A. Calamai H$_{3}^{+}$ is a ubiquitous molecular ion in astrophysical plasmas and has been the subject a variety of experimental and computational studies. We have observed the production and subsequent storage of a significant H$_{3}^{+}$ population following electron bombardment of H$_2$ inside a cylindrical rf ion trap. We combined a simple time-of-flight (TOF) mass spectrometer in tandem with the trap to monitor the temporal evolution of an H$_{3}^{+}$ population as H$_{2}^{+}$ exothermically reacts with H$_2$ after the electron impact interval. At precisely determined times following electron impact, the stored ions are extracted from the trap into an 82- cm flight path terminated by an active-film detector. A 200-MHz digital oscilloscope records the TOF spectrum by monitoring the detector's current output through a 1k$\Omega $ load. As charge- transfer (CT) reactions typically dominate ion losses from the trap for neutral gas pressures $\ge \ 10^{-8}$~Torr, an analysis of the TOF spectra as a function of the delay time until the extraction pulse will yield the production and loss rate of H$_ {3}^{+}$ at a given pressure. A discussion of the apparatus, data associated with the reaction H$_{2}^{+}$ + H$_2$ $\rightarrow $ H$_{3}^{+}$ + H, and a plan for measuring CT rate coefficients between H$_{3}^{+}$ and various neutral target molecules will be presented. [Preview Abstract] |
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EE.00011: Design and Optimization of Solid State NMR Experiments for High Field Applications Seth McNeill, Joanna Long Solid state NMR (SSNMR) has shown promise in examining biophysical problems such as the structure and dynamics of proteins in condensed phases. As magnet technology improves field strength, traditional analytical approaches for developing NMR pulse sequences, such as product operator formalism or average Hamiltonian theory, are no longer sufficient. In SSNMR, this is further confounded by the need to explicitly consider the spatial parts of the internal interactions for unoriented samples. Numerical methods for simulating the behavior of nuclear spins over a powder average have been developed. Concurrently, NMR spectrometers have converted from analog to digital RF technology making possible the development of more sophisticated pulse sequences. We have developed techniques to create optimized pulse sequences using RF fields of arbitrary phase and length leading to robust and attainable experimental parameters in high field conditions. Results for both simulating experimental data and developing more robust sequences for high fields are presented. [Preview Abstract] |
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EE.00012: Synthesis and characterization of P-doped ZnO and (Zn,Mg)O thin films for optoelectronic applications Yuanjie Li, Hyunksoo Yang, Jean Erie, Hyunsik Kim, Stephen Pearton, David Norton ZnO is attracting much attention for its applications in optoelectronic devices due to its wide direct band gap of 3.3 eV and a strong excitonic binding energy of 60 meV. In addition, the band gap of ZnO can be tuned in the range of 3.0 eV - 4.0 eV via alloying with CdO and MgO, which open opportunities for band gap engineering. However, the development of ZnO-based optoelectronic devices has been hindered by achieving low resistivity, high carrier density p-type ZnO. In this study, p-type conductivity in phosphorus-doped (Zn,Mg)O films grown via pulsed laser deposition (PLD) were achieved by adjusting the oxygen partial pressure during the deposition. A hole concentration of 2.7x10$^{16}$ cm$^{-3 }$and mobility of 8.2 cm$^{2}$/Vs were determined from van der Pauw Hall measurements for p-type (Zn,Mg)O:P films. The p-(Zn,Mg)O:P/n-ZnO heterostructures were fabricated on single crystal ZnO. Rectifying characteristics were shown in the vertical structure, confirming the presence of a p-n junction. The systematic study of the relationship of doping concentrations, growth conditions with the transport and optical properties for P-doped ZnO films will also be discussed. R. T. photoluminescence, X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) were utilized to characterize the films properties. [Preview Abstract] |
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EE.00013: Time-resolved far-infrared spectroscopy of superconducting films in a magnetic field Haidong Zhang, D.H. Reitze, C.J. Stanton, D.B. Tanner, R.P.S.M. Lobo, G.L. Carr We report time-resolved, optical pump far-infrared probe measurements of thin superconducting films of NbTiN and NbN in applied magnetic fields. We used a picosecond near-infrared Ti:sapphire laser to pump the film and far-infrared synchrotron radiation from the National Synchrotron Light Source to probe the recombination dynamics of excess quasiparticles. Time resolution is up to a few hundred picoseconds. Despite the presence of the normal cores from vortices in the films, we find that the quasiparticle recombination time does not decrease with magnetic field. We also reported the photoinduced spectrum changes in far infrared transmission between two points on the quasiparticle decay curve in a magnetic field, which provided a measure of the excess quasiparticle density. [Preview Abstract] |
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EE.00014: Teaching the Significance of Angular Momentum Selection Rules in Atomic Spectroscopy R. Seth Smith In physics and chemistry, angular momentum is a crucial concept that is necessary for understanding the structure and behavior of atoms, molecules, nuclei, and elementary particles. One of the goals of the Francis Marion University Modern Physics Laboratory is to teach students the importance of angular momentum in understanding atomic spectroscopy. Early in the term, our students perform an atomic spectroscopy experiment with Hydrogen and study its energy level structure in depth. Later in the term, they are asked to perform a second atomic spectroscopy experiment with Helium. As with Hydrogen, the spectrum of Helium can be shown to be consistent with the energy level model. However, due to the presence of the extra electron, the Helium spectrum is considerably more complex. In fact, in order to accurately explain it, one must consider the effects of angular momentum. In this experiment, students learn that it is impossible to explain the observed spectrum of Helium without introducing the concepts of angular momentum and angular momentum selection rules. In this way, they come to appreciate the importance of angular momentum in understanding atomic spectroscopy. This talk will describe the Helium spectroscopy experiment. Sample results will be presented. [Preview Abstract] |
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EE.00015: High Frequency Electron Paramagnetic Resonance Studies of Single Molecule Magnets Saiti Datta, Amalia Betancur-Rodriguez, Jon Lawrence, Sung-Su Kim, Steve Hill Single crystal samples of different single-molecule magnets (SMMs) were studied by High Frequency Electron Paramagnetic Resonance (HFEPR) in order to characterize their magnetic properties. Multiple studies have been conducted to determine the spin Hamiltonian parameters for different systems, including various Mn and Ni based SMMs. The use of single crystals allows studies in multiple orientations: when the sample's easy axis of magnetization is aligned parallel (perpendicular) to the external field, the axial (transverse) anisotropy parameters can be determined. Variable temperature studies allow the determination of the sign of the axial anisotropy parameters, as well as the energy difference between the ground state and excited states. Multiple orientation studies in a Zn system that is lightly doped with Ni allow determination of the anisotropy parameters for a single Ni$^{+2}$ ion. These results can then be compared to those for the tetranuclear nickel complex consisting of 4 Ni$^{+2}$ ions, enabling an explanation for the fast magnetic quantum tunneling in this system. Finally, analysis of absorption peak linewidths enables characterization of the disorder in SMMs. All of these studies have contributed to a better understanding of the magnetic quantum tunneling behavior in these materials. [Preview Abstract] |
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EE.00016: Two Distinct Monte Carlo Simulations for a Photomultiplier's One-Photoelectron Response Alejandro de la Puente The research focused on the need to obtain an accurate model of a one-photo electron distribution response, which is caused by the dynodic avalanche within a photomultiplier tube (PMT). The Monte Carlo simulations will allow for future direct comparison with the experimental PMT's output and aid in the determination of intrinsic constants that governs the PMT's internal structure and electron gain. The PMT's simulated were model ADIT B29B02H. The simulations were implemented using two distinct Monte Carlos, written mainly in the C++ and C programming languages. The first Monte Carlo was described by an iterative process based solely on the assumption that each photoelectron released from any given dynode by electrons from the previous dynode were correctly described by a Poisson distribution [1]. The only problem found with this implementation was the long computer time needed to run the program. The second Monte Carlo was based on the an statistical theorem, The Central Limit Theorem (CLT), which states that given a random variable of any distribution that has a finite mean (expectation value) and variance; the sample mean of $n $observations will approach the mean of the distribution as $n$ goes to infinity [2]. For both simulations, a one-photoelectron gain was fixed at 1.0x10$^{6}$. Both methods were simulated and a histogram was created and fitted with a Gaussian distribution. From the data and fits, it was concluded that both simulations did not exactly follow Gaussian statistics; reproduced with a high degree of precision the fixed one-photoelectron gain; and that the CLT method could be used over the Iterative Method. [Preview Abstract] |
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EE.00017: New Planetariums For Old David Peterson, Jeannette Myers The audio and visual capabilities of the planetarium at Francis Marion University were upgraded in Fall 2004 to incorporate three Barco CRT projectors and surround sound. Controlled by the Astro-FX media manager system developed by Bowen Technovation, the projectors focus on the 33 foot dome installed in 1978 for the Spitz 512 Star projector. The significant additional capabilities of the new combined systems will be presented together with a review of the planetarium renovation procedure. [Preview Abstract] |
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EE.00018: Magnetic Field Effect on the dielectric properties of the Single Molecule Magnet V$_{15}$ Relja Vasic, Narpinder Kaur, James Brooks, Naresh Dalal Single-molecule hysteresis and quantum tunneling of magnetization (QTM) have made single molecule magnets(SMMs) among the most widely studied compounds in the past decade. Best known SMMs are Mn$_{12}$-acetate and Fe$_{8}$Br$_{8}$. Recently a polyoxovanadate compound K$_{6}$[V$_{15}$As$_{6}$O$_ {42}$(H$_{2}$O)].8H$_{2}$O, henceforth V$_{15}$, has been shown to exhibit some of the properties of SMMs despite an S=1/2 ground state, and no evident potential energy barrier to the reorientation of the magnetic moment. In this study we have investigated magnetic field effects on the dielectric properties of V$_{15}$ using ac impedance technique. In preliminary experiments over the frequency range of 1-100kHz and temperature range of 10-300K, V$_{15}$ is found to exhibit three independent relaxation mechanisms. On the application of magnetic field, the dielectric relaxation peaks shift towards higher temperatures. The presentation will discuss details of sample preparation, measurement techniques and theoretical interpretation of this newly observed effect. [Preview Abstract] |
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EE.00019: Temperature Transformation Equations for Introductory Physics H.L. Neal In every physics textbook, the equations presented for converting from one temperature scale to another are written inconsistently with respect to unit conversion. We propose temperature transformation equations that are consistent with the way students are taught to convert units. [Preview Abstract] |
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EE.00020: Mn-55 NMR Relaxation and Full Angular Dependence of Mn12-Bromoacetate Andrew Harter, Nicole Chakov, Brian Roberts, Randy Achey, Arneil Reyes, Phil Kuhns, George Christou, Naresh Dalal The phenomenon of quantum tunneling of magnetization (QTM) observed first in Mn12-acetate has attracted considerable attention lately, but its origin is still not fully clear. One important question is the role of lattice-solvated molecules and the consequent lowering of~local site symmetry from axial to non-axial. We have developed single crystal NMR techniques to probe this question more deeply. In particular, we have carried out Mn-55 measurements on single crystals of Mn12-acetate and its bromoacetate variant. Spin-lattice measurements down to around 300mK have been studied in zero field while a complete angular dependence study was undertaken at 2K and 1.75T. Angle variation studies clearly show that the local symmetry around the Mn(4+) nuclei is non-axial. Details of the NMR technique, the important role of sample preparation (single crystal vs oriented powder) and the relationship of the data to the QTM mechanism will be discussed. [Preview Abstract] |
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EE.00021: Ferromagnetism and short range order in Pt-Co and Pt-Mn alloys Rixio Parra Alloys of Pd and Pt with magnetic impurities behave magnetically very much alike. For example, recent diffuse neutron scattering measurements in single crystals show that Pt-Mn alloys tend to become ferromagnetic as the concentration of Mn is lowered. Pt-Mn alloys with concentrations c = 3 at. percent Mn show ferromagnetism and above 5 at. percent behave as spin glasses, turning at higher concentrations as antiferromagnets. However, Pt-Mn become ferromagnetic at concentrations above 8 at. percent Mn, the atomic structure changes to a Cu3Au type, and atomic short range order is observed, with preference of Mn to have Pt atoms as first neighbour. In this work we analyzed the experimental data of Pt-Mn and Pt-Co, using a ferromagnetic model that has been applied to other Pt and Pd alloys, where the impurity is magnetic (Fe, Co or Mn). [Preview Abstract] |
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EE.00022: Core-shell nanoparticles as scavengers for hydrophobic molecules in biological systems Jeffrey Wong, Jorge Ch\'{a}vez, Randolph Duran Core-shell nanoparticles containing hydrophobic cores and hydrophilic shells were synthesized based on a tertiary microemulsion system. Due to their hydrophobic interior, this system is proposed to work as a scavenger of non polar species, like pesticides or drugs present in concentrations higher than what the body can tolerate. The ability to control the core and shell sizes using different molecules to fill the core was studied with different techniques. Hydrophobic fluorescent dyes were used as model non polar molecules to study the uptake abilities of the system synthesized. Derivatization of the surface of the core-shell particles with different groups, including biotin and poly(ethylene glycol) was performed to improve the biocompatibility of the system. Binding to streptavidin via the biotin units on the surface was performed to study the biocompatibility of the derivatized nanocapsules in biological relevant systems. [Preview Abstract] |
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