Bulletin of the American Physical Society
2008 Spring Meeting of the Ohio-Region Section of APS
Volume 53, Number 3
Friday–Saturday, March 28–29, 2008; Youngstown, Ohio
Session P1: Poster Session: 4:15 pm - 6:00 pm |
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Chair: Patrick Durrell, Youngstown State University Room: Moser Hall Lobby |
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P1.00001: An analysis of the tensile strength of twisted fiber structures Carl Starkey, Cavendish McKay We are interested in modeling the interaction between elements within a typical twisted fiber structure such as a thread or cable using numerical analysis techniques. A twisted cable or thread requires frictional forces between its constituent filaments to stay together and to transmit tension along its length. Fine scaled studies of these forces and the properties on which they depend are computationally intensive due to the large number of filaments involved. The current study is a preliminary look at the interactions between individual filaments, starting with simple tensile strength tests and working up to sliding friction between bundled fibers. The primary research tool utilized in this project is the LS-DYNA finite element analysis software package. [Preview Abstract] |
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P1.00002: Remote respiration sensing using millimeter-wave radar systems Erik Bryan, Charles Phelps, Joshua Yoakum, Anu Grover, Izaak Kemp, Douglas T. Petkie Two radar systems capable of detecting directional displacement were used to measure the movement of a subject's chest wall due to respiration. The first system uses a Michelson interferometer setup and a binary-frequency-shifted signal on a 120 GHz carrier to obtain I (in-phase) and Q (quadrature) signals. The relative phase between I and Q is used to determine the displacement. The second system is a heterodyne transceiver operating near 240 GHz, which returns the I and Q signals directly through IF (intermediate frequency) signal processing. Both systems have been able to determine respiration rates from data taken facing a subject head-on. We will present an overview of both systems along with representative data. [Preview Abstract] |
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P1.00003: Terahertz Spectroscopy of Water for Combustion Monitoring Ross Bobb, Douglas T. Petkie The THz spectral features of water are sensitive to both temperature and pressure and the observed intensity ratio between selected transitions can provide a measurement of temperature. This coupled with the THz transmissive properties of soot and fuel make THz spectroscopy a candidate for monitoring combustion processes. We will discuss system designs for such an application and present spectral simulations and measurements of several water transitions. [Preview Abstract] |
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P1.00004: Large Amplitude Oscillations of a Double Pendulum Jeffrey M. Gerres, Robert M. Jacobs, Sara F. Kasun, Margaret E. Bacon, Chakravarthi M. Nagolu, Erin L. Owens, Kevin F. Siehl, Marshall Thomsen, Jon S. Troyer The nature of the normal modes of oscillation in the small angle regime of a double pendulum is well established. However, for large amplitude oscillations, a closed form solution of the differential equations of motion does not exist. Using Lagrange formalism, we explore both the in-phase and out-of-phase normal modes of oscillation of a double pendulum as a function of the mass ratio of the two bobs and their initial angular positions. We conduct the analysis using MatLab, where we initially verify our code in the known small amplitude limit. Among our results we find that certain symmetries between the in-phase and out-of-phase normal modes that exist in the small amplitude limit are no longer present at large amplitudes. [Preview Abstract] |
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P1.00005: The decoloration of organic dyes by pen-like plasma torch Talun Sung, Chung-Ming Liu, Gin-Gou Yan, Shinriki Teii In this work, the decoloration of organic of dyes (sky blue) by pen-like plasma torch was investigated. The pen-like plasma touch was powered by 13.56 MHz RF. The center stainless steel tube was anode which surrounded by ceramic tube as insulator media. At the end of pen, one cathode was covered by the stainless steel electrode. The argon gas flown the tube was excited into plasma by RF field. Because Ar plasma torch activate the water into OH and O radicals, the dyes was reacted with these radicals and the color bonds were broken by these active species. The decoloration process has been investigated by different power, the volume of dyes solution and time. The decoloration is determined by measuring the absorption of the dye solution with a monocrometer. The percentage of decoloration = (the absorption before plasma treatment -- the absorption after plasma treatment) / (the absorption before plasma treatment -- the absorption of pure water). The experiments have shown that the decoloration is proportional to RF power and treatment time but inversely proportional to the volume of dye solution. [Preview Abstract] |
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P1.00006: Analytical expression for the sheath edge around wedge-shaped cathodes T.E. Sheridan The sheath is the boundary layer separating a quasi-neutral plasma from a material electrode. Understanding the sheath is important for numerous applications, including plasma-based ion implantation, plasma etching of semiconductors, plasma assisted electrostatic cleaning, and Langmuir probes. In a 1D planar geometry, the Child-Langmuir (CL) law describes the sheath when the bias on a negative electrode, i.e., a cathode, is much greater than the electron temperature. In this case, the sheath width $s$ is an eigenvalue of the problem. In 2D, the sheath edge is an unknown line (an ``eigen-boundary") which is determined by a set of coupled, nonlinear, partial differential equations. I have found an expression for the sheath edge around a 2D wedge-shaped cathode with included angle $\theta_w$. In polar coordinates $\left(r,\theta\right)$, the sheath edge is a solution of $r\sin\left(a\theta\right)=as$ where $s$ is the planar sheath width far from the corner and $\theta_w=2\pi - \pi/a$, so that $a=1/2$ gives a knife edge, while $a=2/3$ gives a square corner. This result is verified by comparison with the numerical solutions of Watterson [P. A. Watterson, J. Phys. D $\bf{22}$, 1300 (1989)]. [Preview Abstract] |
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P1.00007: Large Thermoelectric Figure of Merit in Thin Ablated Skutterudite Films Harsha Attanayake, Dilupama Divaratne, Robert Boughton Thin 40{\%} lanthanum-filled skutterudite films were prepared by pulsed laser ablation on glass substrates. In general, laser ablated film characteristics exhibit up to 70{\%} amorphous structure and vary in thickness by about 20{\%} from center to edge. The thermoelectric figure of merit was determined using Harman's$^{1}$ method at room temperature, which involves voltage measurement under isothermal and adiabatic conditions. A total of 16 samples prepared in three ablation runs were measured as a function of substrate thickness in order to determine the limiting figure of merit (\textit{ZT = S}$^{2}$\textit{T/$\rho \kappa $}${\rm p}{\rm g}$n the thin film geometry. The average film thickness was determined to be 95 \textit{nm}. The extrapolated behavior predicts a very large value of the thermoelectric figure of merit for this material, approaching 15, far exceeding values obtained with bulk samples. We attribute the high value to several possible factors: enhanced Seebeck coefficient and size limited thermal conductivity in both electronic and lattice components. Possible applications are discussed. 1. T. C. Harman, S. E. Miller, H. L. Goering, \textit{J. Phys. Chem. Solids},\textbf{ 2}, 181 (1957). [Preview Abstract] |
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P1.00008: G3 Electron Affinities of Silicon and Germanium Clusters Peter Deutsch We review binding energies and electron affinities for atomic silicon and germanium obtained by G3 ab inito theory$^{1}$ with respect to potentially significant differences between what we obtain and what is in the experimental literature. We focus on the electron affinities of the five atom clusters, reviewing the impact of using different types of geometries for the higher level calculations. Specifically we review the impact on electron affinities of using geometries with more diffuse functions and more polarization functions than are employed in the G3 calculations. $^{1 }$L. A. Curtiss et. al. J. Chem. Phys. 114, 9287 (2001) and references therein. [Preview Abstract] |
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P1.00009: Superconducting to Insulating Phase Transition in Current-Biased Josephson Junction Arrays C.D. Porter, D. Stroud We present a variational approach to treat the metastable superconducting state in an array of small Josephson junctions driven by an applied current. The approach is a generalization of one previously used to treat such an array at zero applied current. We find that, for a given array, a superconducting to non-superconducting transition can be achieved as a function of applied current, or by varying the direction of the applied current at fixed magnitude. This transition can be observed for a wide range of junction parameters including the range in which single junctions are tuned to be two-level systems. [Preview Abstract] |
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P1.00010: Rigidity and pH dependent Morphology of Beta-Lactoglobulin Spherulites Lisa Gayetsky, Douglas Armstead Beta-Lactoglobulin is a milk protein that will denature in acidic solution (less than 2.0 pH) and if heated for extended periods (greater than 18 hours) it will form radial structures called Spherulites. Spherulites, along with the amyloid fibrils that compose them, are of practical importance because they form in the human body and cause the amyloidosis diseases. Different amyloidosis are caused by different types of denatured proteins occurring in different parts of the body. Since it is believed that Spherulite formation is a generic protein characteristic, Beta-Lactoglobulin is a legitimate and easy to use protein to study these structures. In this study we are quantifying the shape of Beta-Lactoglobulin Spherulites to determine if the pH of the protein solution has an impact on the morphology due to side chain interactions or other causes. We are also testing the rigidity of these structures to determine the relevance of small shape changes. [Preview Abstract] |
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P1.00011: Using the dual-wavelength fluorophore LysoSensor Yellow/Blue for acidic-pH sensing at high hydrostatic pressures Hector Michael de Pedro, Paul Urayama Spectroscopic techniques using dual-wavelength fluorophores are being developed for pH sensing under biologically-relevant high-pressure conditions (up to 1000 atm). Here we present the effects of pressure on the acid-base equilibrium of a commerically-available fluorophore used for sensing acidic pH -- LysoSensor Yellow/Blue DND-160. Previous studies on the pressure response of near-neutral pH fluorophores including seminaphthofluoresceins and seminapthorhodafluors, show that the predominant effect is a pressure-dependent change in the equilibrium constant of the fluorophore's acid-base reaction. That is, emission spectra from the protonated and deprotonated fluorophore forms did not show significant pressure sensitivity. For DND-160, the emission spectrum of the deprotonated form is highly pressure sensitive, likely due to effects on the rotational dynamics of the aromatic ring motif. Nonetheless, spectra remain interpretable in terms of its associated acid-base reaction, indicating that DND-160 is still useful for high-pressure, low-pH sensing. [Preview Abstract] |
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P1.00012: The Temperature and Thickness Dependence of Resistivity in Thin Copper Films Daniel Stanley, Dennis Kuhl The bulk resistivity of a material depends on its temperature, and is a well studied affect. In thin metal films, however, the contribution to resistivity due to scattering from the surface of the film is expected to be significant. As the film grows thicker, surface scattering eventually becomes insignificant and the temperature dependent bulk resistivity of the material dominates. We present fits of experimental data to a Fuchs-Sondheimer classical size effect model to test the prediction that surface scattering is the dominant mechanism in thin copper films. We have tried to isolate temperature-dependent effects by monitoring the temperature of the film during growth in a thermal evaporator. Widely varying initial resistivity data suggests early film growth consists of island formation. [Preview Abstract] |
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P1.00013: Effects of Hydrostatic Pressure on the Transport and Magnetic Properties of Sb$_{2-x}$Cr$_{x}$Te$_{3}$ Thin Films Matthew L. Bowers, Jeffrey S. Dyck, Yi-Yiunn Chien, Ctirad Uher Thin film samples of Molecular Beam Epitaxy grown diluted magnetic semiconductor Sb$_{2-x}$Cr$_{x}$Te$_{3}$ (x=0.15) are being studied in an effort to understand the electrical and magnetic mechanisms that cause these and other similar DMS materials to undergo a ferromagnetic transition at low temperature. By taking advantage of the fact that hydrostatic pressure alters the carrier concentration in these materials, our aim is to examine the carrier-mediated magnetic interactions in this material. Electrical resistivity and Hall effect of these films were measured as a function of temperature from 2 K -- 300 K and pressure up to 1.38 GPa. We find that pressure modestly increases the carrier concentration, while decreasing the resistivity. Moreover, ferromagnetism is enhanced as evidenced by the fact that the coercive field in the anomalous Hall effect increases with pressure and the ferromagnetic transition temperature increases modestly from 50 K to 60 K. Comparisons will be made to the related compound Sb$_{1.85}$V$_{0.15}$Te$_{3}$. [Preview Abstract] |
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P1.00014: Effect of Electric Field on Phonoritons in Semiconductors Michael Jayson Price, Que Huong Nguyen Under illumination of high-intensity electro-magnetic radiation near the resonance, the occupation number of polaritons of the same mode in a semiconductor sample is large, leading to significant interaction between polaritons and phonons. This interaction leads to the formation of a new kind of elementary excitation called phonoriton, a coherent superposition of excitons, photons, and longitudinal acoustic phonons under Brillouin scattering of intense polaritons. The phonoritons have been studied theoretically and experimentally and have been found in Cu2O. In this work we study the effect of an electric field on phonoritons inside semiconductors. The shift of photoritons as the result of applying electric field and the quadratic Stark effect is found. The effect suggests an experiment to observe the phonoritons. [Preview Abstract] |
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P1.00015: Conformation and collapse of a square-well chain in a square-well solvent Passang Dorji, Mark Taylor Interaction-site chains provide coarse-grained yet realistic models for polymers. Such models have long been used to study the collapse transition observed for polymers in dilute solution. In most of these studies, the variation in solvent quality (which drives the collapse) is treated implicitly through an effective polymer-polymer interaction and thus explicit polymer-solvent coupling is ignored. This coupling is expected to be important in the collapse transition due to the dramatic change in polymer conformation and exposure to solvent. Although a formally exact treatment of polymer-solvent coupling can be constructed, the required many-body solvation potential is not practical to compute. We have recently shown that for short chain-in-solvent systems this many-body solvation potential can be made tractable via an ``exact'' decomposition into a \textit{set} of two-site potentials [1]. Here we use these exact short chain results to construct approximate two-site solvation potentials for long square-well chains in solvent [2]. These solvation potentials are used to study the role of solvent in both driving and inhibiting chain collapse in square-well systems. [1] M. P. Taylor and G. M. Petersen, J. Chem. Phys. \textbf{127}, 184901 (2007). [2] M. P. Taylor and S. Ichida, J. Polym. Sci., Part B: Polym. Phys. \textbf{45}, 3319 (2007). [Preview Abstract] |
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P1.00016: Computational study of acoustic solitary waves in 2D complex plasma M.J. Garee, T.E. Sheridan A one-dimensional, nonlinear model has been developed for dust-acoustic (DA) waves in a two-dimensional complex plasma. In our model, identical charged dust particles reside on a periodic triangular lattice with lattice constant $a$. These particles are constrained to move in one dimension, and interact with each other via a screened Coulomb force with Debye length $\lambda_D$. The model is used to compute the dependence of the DA wave speed on the screening parameter $\kappa=a/\lambda_D$. Computed wave speeds show excellent agreement with theoretical predictions, thereby verifying the model. Total energy is also conserved, as it should be. Localized velocity perturbations are found to evolve into compressive solitary waves and to propagate through the lattice with speeds greater than the DA wave speed. Rarefactive solitary waves are not observed. We intend to characterize overtaking collisions of solitary waves in this system to determine if the phase shift predicted by Korteweg--deVries (KdV) theory occurs, and to compare computed solitary wave widths, amplitudes and speeds to the scalings predicted for KdV solitons. [Preview Abstract] |
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P1.00017: Conformal Mapping as a Tool for Solving Laplacian Problems in Physics Harrison Potter, Craig Howald Source problems in two-dimensional Laplacian field theory are studied using the tools of complex analysis, specifically those of conformal mappings.~ Generalizations of these techniques to interval sources are then investigated. [Preview Abstract] |
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P1.00018: PLANCK tests General Relativity Dmitri Rabounski, Larissa Borissova If the origin of a microwave background (EMB) is the Earth, what would be its density and dipole anisotropy at different altitudes? The density of the EMB is answered through Einstein's equations containing the electromagnetic field. The dipole anisotropy is analysed by using the geodesic equations for photons (mediators for electromagnetic radiation). It is shown that the EMB decreases with altitude: its density at the 900 km altitude (COBE) is 0.68 times less than that at the 25 km altitude (U2 aeroplane), while at the 2nd Lagrange point (1.5 mln km, WMAP and PLANCK satellites) it should be only 10$^{-7}$ of the value detected by U2 or COBE. The dipole anisotropy of the EMB doesn't depend on altitude. WMAP indicated the same anisotropy of the background at the 2nd Lagrange point that near the Earth. When, in addition to it, PLANCK will manifest the 2.7 K monopole microwave signal deceased at the 2nd Langrange point, it will be a new experimental verification of General Relativity. This result is in support to the experimental analysis, according to which the 2.7 K microwave background is not of cosmic origin, but of the Earth, and is generated by the oceans. [Preview Abstract] |
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P1.00019: Characterization of Electrospun Titania Nanofibers Nicole Schafer, Nicholas Bjelac, Nenad Stojilovic, Soo Jin Park, George Chase Titania (TiO2) nanofibers formed by electrospinning are characterized by a variety of techniques. Electrospinning is a simple, versatile, and inexpensive method for producing relatively long fibers whose diameters are typically on the order of several hundred nanometers. Titania is used in optical and electrical applications but is also photocatalytic and is suitable for use in high-temperature environments. In our experiments electrospun TiO2 nanofibers are investigated using a range of techniques such as field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and infrared (IR) spectroscopy. [Preview Abstract] |
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P1.00020: Microscopy of Metal Oxide Nanofibers Nicholas Bjelac, Nicole Schafer, Nenad Stojilovic, Soo Jin Park, George Chase Using electrospinning we are able to produce a variety of metal oxide nanofibers (e.g., Al2O3, TiO2, ZnO) that are primarily of interest in high-temperature applications. In particular nanofibers are obtained from electrospinning a metal precursor solution mixed with organic polymers. Pure metal oxide nanofibers are then obtained by removing precursors by annealing. We study the surface morphology of these electrospun nanofibers using field-emission scanning electron microscopy and atomic force microscopy. [Preview Abstract] |
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P1.00021: Two dimensional Confinement of 5CB between Lipid Bi-layers Bradley Kirkwood, Kevin Sobczak, Dustin Hemphill, Eric Hardin, Rizwan Mahmood We have confined 5CB (4-Cyano-4'-Pentyl-1, 1'-biphenyl), a calamitic thermotropic liquid crystal, between lamellar bilayers formed by the lyotropic lipid DDAB (diodecyldimethylammoniumbromide). DDAB bilayers were swollen by the addition of an anisotropic liquid, 5CB. Initial phase transition and optical birefringence data have suggested demixed phase(s) 25\% $=$5CB $= $85\% in 88\% (DDAB + 25\% water). Isotropic to Lamellar transition was observed in all the samples of less than 27\% 5CB. [Preview Abstract] |
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P1.00022: Finite Element Method Simulations of Metamaterial Devices at Terahertz Frequencies Jason Deibel, Scott Eilerman Negative index materials that operate at terahertz frequencies can be difficult to model, fabricate, and characterize. We use the finite element method to simulate the interaction between negative index metamaterials and electromagnetic waves. A simple straight-wire pair structure is used to create a unit cell structure with an intended resonant frequency at 0.1 THz. Several unit cells are placed on opposite sides of a silicon substrate in order to form the modeled metamaterial device. Preliminary simulation data shows a strong, but narrow, drop in the transmitted power at approximately 0.125 THz. Further tests are planned to examine this dip and to fine-tune the frequency response by adjusting the unit cell structure and the substrate thickness and refractive index. [Preview Abstract] |
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P1.00023: Combined, Confocal Excitation Emission Spectroscopy of Neodymium-doped Gallium Nitride Martin Arienmughare Gallium Nitride epitacial layer doped with Nd3+, show strong RE specific photoluminescence which depends on incorporation site, the spatial distribution of these sites, concentration of ions, on how the sample was prepared. We used two techniques: Combined Emission-Excitation Spectroscopy (CEES) and Confocal Microscopy (CM), to `find' the incorporation sites and their spatial distribution, using a tunable laser with a wavelength between 600-630nm and observing the emission between 911nm and 946nm. Using the spectroscopic data from CEES a complete energy level scheme was constructed; it included excitation and emission peaks that arose from electron-phonon coupling. The CM experiments were performed at low temperature ($\sim $4K), over a range of about 30$\mu $m * 30$\mu $m on the sample; and with an excitation wavelength of 612.7nm corresponding to a predicted emission wavelength of about 915.84nm. When normalized, the photoluminescence intensity shift of the emitted wavelength is about 10{\%}, while the wavelength ranges from 915.81nm to 915.86nm proving that part of the emission line broadening observed in spatially unresolved CEES is due the spatial inhomogeneities of the samples. Most notably, we found regions that are several micrometers in size, which show the most significant changes. [Preview Abstract] |
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P1.00024: Chasing a shadow: Student participation in lunar occultation observations Kenneth Coles, Ronald Freda Occultations, or blocking, of stars by the Moon have been observed and recorded by amateur astronomers since Dunham* discovered their usefulness a half century ago. Grazing occultations of the north or south polar regions of the Moon are of particular interest. These provide high-resolution (as fine as 50 m) constraints on lunar topography that is still poorly covered by radar measurements from Earth and robotic spacecraft. Moreover, plans for future lunar exploration include a possible outpost at the south pole. Grazing occultations can also constrain the positions and separation of double stars. Undergraduate students participate in our grazing occultation observations. Simple telescopes and audio recording, referenced to a base station located in space and time by GPS, can cover a chord across the limb of the Moon. We plan our next group effort at Indiana, PA for a 2008 April 7 (local time) graze of the lunar north pole by a magnitude 6 double star in Aries. \newline *Nugent, R., editor, 2007, The International Occultation Timing Association Observer's Manual: http://www.poyntsource.com/IOTAmanual/index.htm. [Preview Abstract] |
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P1.00025: Rotationally resolved fluorescence spectroscopy of molecular iodine Christopher Lemon, Sebastian Canagaratna, Jeffrey Gray Vibration-electronic spectroscopy of I$_{2}$ vapor is a common, important experiment in physical chemistry lab courses. We use narrow bandwidth diode-pumped solid state (DPSS) lasers to excite specific rotational levels; these lasers are surprisingly stable and are now available at low cost. We also use efficient miniature fiber-optic spectrometers to resolve rotational fluorescence patterns in a vibrational progression. The resolution enables thorough and accurate analysis of spectroscopic constants for the ground electronic state. The high signal-to-noise ratio, which is easily achieved, also enables students to precisely measure fluorescence band intensities, providing further insight into vibrational wavefunctions and the molecular potential function. We will provide a detailed list of parts for the apparatus as well as modeling algorithms with statistical evaluation to facilitate widespread adoption of these experimental improvements by instructors of intermediate and advanced lab courses. [Preview Abstract] |
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P1.00026: Influence of passivation on the transport study of AlGaN/GaN: A focus on high T Hall effect characterization. J. Daniel, S. Elhamri, R. Berney, M. Ahoujja, W. Mitchel, J. Roberts, P. Rajagopal, J. Cook, E. Piner, K. Linthicum Hall effect measurements on two samples were used to study the impact of elevated temperatures (300-675 K) on the transport parameters of AlGaN/GaN grown on Si. The two samples had similar growth structures, except one sample (sample A) was passivated with SiN and the other (sample B) was not. The room T mobility and carrier density, n, for sample A were 1510 cm$^{2}$/Vs and 8.2 x 10$^{12}$ cm$^{-2,}$ and for B were 1510 cm$^{2}$/Vs and 9.42 x 10$^{12}$ cm$^{-2}$, respectively. Although these two parameters were similar at room T for the two samples, the T dependences of n were very different. Whereas n for sample A was found to be relatively insensitive to T, the carrier density for sample B showed a strong T dependence. Its n increased to 3.75x10$^{13}$ cm$^{-2}$ at 675 K. It is worth noting that the T dependence of n observed in sample B was confirmed on others samples with similar growth conditions. Unlike the results of the high Tstudy, low T Hall measurements did not show a strong difference between the two samples. Magnetoresistance measurements at 1.2 K in magnetic fields up to 8 T indicated the presence of Shubnikov-de Haas oscillations for sample A but not for sample B. However, after illumination oscillations were observed in sample B. While both samples were sensitive to illumination, its impact was observed to be much stronger in sample B than in sample A. [Preview Abstract] |
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P1.00027: Effects of electron radiation on the electron transport properties in AlGaN/GaN heterostructure Mo Ahoujja, S. Elhamri, R. Berney, M. Hogsed, Y.K. Yeo, R. Hengehold The effects of electron irradiation on the electron transport properties in a Al$_{0.27}$Ga0$_{.73}$N/GaN single heterostructure grown by radio-frequency plasma activated molecular beam epitaxy on sapphire substrates were investigated by variable temperature dependent Hall-effect. The Hall results show that both the two-dimensional carrier concentration and carrier mobility suffered a reduction of 13 {\%} and 23{\%}, respectively, at room temperature. This in turn led to about a 150 {\%} increase in sheet resistivity. While sheet carrier concentration remains relatively constant with temperature before and after irradiation, the mobility is greatly affected at low temperatures. It is believed that at low temperatures, scattering by ionized defects is the most dominant effect. Hence, the 1.0 MeV electron radiation doses used in this investigation ($\sim $ 1x10$^{17}$ cm$^{-2})$ and the accompanying defect introduction rates are relevant to HEMT device operation. [Preview Abstract] |
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P1.00028: Thermal Conductivity of Polycrystalline PbTe with PbSe Nanoparticle Additives Ian M. Steward, Jeffrey S. Dyck, Yixin Zhao, Clemens Burda Thermoelectric materials (TEMs) are semiconductor materials that use the Seebeck and Peltier effects to convert a temperature difference into an electric potential and vice versa. All thermoelectric materials are characterized by a figure of merit, ZT, which is directly correlated to the thermoelectric energy conversion efficiency. One option to obtain improved ZT values is to lower the thermal conductivity of the TEM. Nanostructuring of traditional TEMs is one avenue toward lowering thermal conductivity, hopefully without significantly diminishing the electrical properties. Pellets of bulk, polycrystalline lead telluride with varying concentrations of PbSe nanoparticle additives were prepared by pressing mixed powders. Measurements of thermal conductivity were performed in the temperature range 6 K -- 300 K. The data were compared to a theoretical model in an attempt to link the temperature dependent behavior of the thermal conductivity to the synthesis parameters, nanoparticle concentration, and sample morphology as revealed through Scanning Electron Microscope images. [Preview Abstract] |
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P1.00029: Effect of PbSe Nanoparticle Addition on the Thermoelectric Properties of Bulk, Polycrystalline PbTe Diego Hernandez, Jeffrey Dyck, Yixin Zhao, Clemens Burda Thermoelectric materials are able to convert heat energy into electrical energy and vise versa. Theorists predict that creating nanometer-sized inclusions in traditional thermoelectric materials may improve thermoelectric properties by scattering acoustic phonons, which transmit thermal energy, more strongly than free charge carriers. To study the effect, pellets of bulk, polycrystalline lead telluride with varying concentrations of PbSe nanoparticle additives were prepared by pressing mixed powders. Measurements of electrical resistivity, thermal conductivity, Seebeck coefficient, and Hall mobility were made from 10 K to 300 K. Preliminary measurements found that the thermoelectric figure of merit was not enhanced in samples containing PbSe nanopartiles in the temperature range of our measurements, but further tests may show the true potential of nanostructuring. [Preview Abstract] |
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P1.00030: Use of Shubnikov-de Haas measurements on AlGaN/GaN structures to investigate the effective mass of GaN. E.J. Timko, S. Elhamri, R. Berney, M. Ahoujja, W.C. Mitchel Gallium Nitride and its related alloys and heterostructures have been extensively studied in many research labs worldwide. This interest is driven by the many applications these materials offer in both the optical and electronic device areas. A key parameter of GaN is its electron effective mass and published reports continue to indicate lack of consensus on the numerical value of this parameter. The focus of our study is to use Shubnikov-de Haas measurements on several samples grown on various substrates to investigate the effective mass of GaN. The strength of the study stems from the fact that a large number of samples grown under different conditions on various substrates will be used in this project. This study will allow us to determine if the effective mass is sensitive to the carrier density and/or the value the magnetic field as recent reports suggest. To study the impact of the carrier density on the electron effective mass, we will investigate samples with different carrier densities and use illumination to vary the carrier density within the same sample. Use of illumination to change the carrier density is particular useful as it allows the study of the effective mass as a function of the carrier concentration without having to worry about structural variations that one must take into account when looking at different samples. The results of this comprehensive study will be presented. [Preview Abstract] |
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P1.00031: An Investigation of the Role of Friction in the Motion of a Tippe Top Elisabeth Kager, Craig Howald, Dennis Kuhl The time it takes a Tippe Top to turn over was measured as a function of friction. The reproducibility of the measured tipping time was also examined. Two experiments were conducted: One to measure a frictional figure of merit and the second to test the time it takes the Tippe Top to tip on three surfaces with varying friction. The three surfaces used were glass, Teflon, and Vinyl. Several runs of spinning Tippe Tops were recorded by means of a video camera. The data was analyzed by extracting the angular position and the angular velocity of the Tippe Top. By graphing the angular velocity vs. time and using the slope of the line, a frictional figure of merit was found. The time it took the Tippe Top to tip in each case was also determined. [Preview Abstract] |
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P1.00032: Nonlinear motion of Supersonic Dust particles in Complex Plasmas William Theisen A strongly-coupled dusty plasma disk consisting of electrically charged microspheres was arranged in a hexagonal lattice in a horizontal plane and levitated in a parabolic potential well. Dust particles traveling at supersonic velocities below the two dimensional Coulomb crystal were studied. Trajectory plots of one, two and three supersonic particles were analyzed using common nonlinear techniques. [Preview Abstract] |
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P1.00033: Plasma Treatment of Pulsed DC Magnetron Sputtered Indium Tin Oxide Amber Reed, John Jones, Doug Petkie Crystalline indium tin oxide (ITO) is optically transparent and electrically conductive. ITO deposited with magnetron sputtering is amorphous. Typically these films are treated with post-deposition annealing to crystallize the films. The annealing temperature of $>$300\r{ }C required can prohibit deposition on polymer substrates. In the current work, the effects of pulse parameters in mid-frequency pulsed dc on as-deposited film composition and structure were investigated, as well as a post-deposition RF plasma treatment process designed to promote crystallization of the films on polymer substrates from ion bombardment. Raman spectroscopy was used to show that the degree of film crystallization was dependent on the frequency and duty factor of the pulsed power supply used for deposition, as well as the parameters selected for the post-deposition RF plasma treatment. The film's conductivity was measured before and after the plasma treatment. XPS was used to determine dependence of the processing parameters on the chemical composition of the ITO films. [Preview Abstract] |
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P1.00034: Forensic Analysis of Lunar Dust and Spacesuit Mitigation J. Anneliese Lawrence, John Lindsay, Sarah Noble A study was performed by authors to analyze dust lifted from Jack Schmitt's EVA space suit from Apollo 17 for mineralogy and grain size distributions for the 1,200 sampled particles. The grains were viewed through an SEM, photographed and analyzed using EDS equipment and mathematical computations. This study yielded counterintuitive results to be discussed in this presentation. Also discussed are magnetic properties of lunar dust. [Preview Abstract] |
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