Physical Sciences and Mathematics Commons^™

Laser-Powered Thermoelectric Generators Operating At Cryogenic Temperatures, S. R. Harutyunyan, V. H. Vardanyan, A. S. Kuzanyan, V. R. Nikoghosyan, S. Kunii, K. Winzer, K. S. Wood, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

A thermoelectric generator, operating in a cryostat at liquid helium temperatures, is described. Energy to the generator is supplied via an external laser beam. For this prototype device the associated heat load at permanent operation is comparable with the heat load associated with power delivery via metallic wires. Estimates indicate that still better performance can be enabled with existing thermoelectric materials, thereby far exceeding efficiency of traditional cryostat wiring. We used a prototype generator to produce electric power for measuring critical currents in Nb₃Sn-films at 4K.

Kinetic Evaluation Of Human Cloned Coproporphyrinogen Oxidase Using A Ring Isomer Of The Natural Substrate, Marjorie A. Jones, Christopher L. Cooper, Timothy D. Lash

Faculty Publications – Chemistry

Background: The enzyme coproporphyrinogen oxidase (copro'gen oxidase) converts coproporphyrinogen-Ill (GIII) to protoporphyrinogen-IX via an intermediary monovinyl porphyrinogen. The A ring isomer coproporphyrinogen-IV (C-IV) has previously been shown to be a substrate for copro'gen oxidase derived from avian erythrocytes. In contrast to the authentic substrate (GIII) where only a small amount of the monovinyl intermediate is detected, C-IV gives rise to a monovinyl intermediate that accumulates before being converted to an isomer of protoporphyrinogen-IX. No kinetic studies have been carried out using the purified human copro'gen oxidase to evaluate its ability to process both the authentic substrate as well as analogs. …

Systematic, Multisite Short-Range-Order Corrections To The Electronic Structure Of Disordered Alloys From First Principles: The Kkr Nonlocal Cpa From The Dynamical Cluster Approximation, D. A. Biava, Subhradip Ghosh, Duane D. Johnson, W. A. Shelton, Andrei V. Smirnov

Duane D. Johnson

Although the Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) is used widely to configurationally average and get electronic structures and energies of disordered alloys, a single-site CPA misses local environment effects, including short-range order (SRO). A proposed nonlocal CPA (NLCPA) recovers translational invariance of the effective medium via k-space coarse graining from the dynamical cluster approximation (DCA), where corrections are systematic as cluster size increases. We implement a first-principles KKR-NLCPA/DCA and show the effects of environment, including SRO, on the electronic structures of fcc CuAu and bcc NiAl.

Investigation Of The Superconducting Properties Of Niobium Radio-Frequency Cavities, Gianluigi Ciovati

Physics Theses & Dissertations

Radio-frequency (rf) superconducting cavities are widely used to increase the energy of a charged particle beam in particle accelerators. The maximum gradients of cavities made of bulk niobium have constantly improved over the last ten years and they are approaching the theoretical limit of the material. Nevertheless, rf tests of niobium cavities are still showing some "anomalous" losses (so-called "Q-drop"), characterized by a marked increase of the surface resistance at high rf fields, in absence of field emission. A low temperature "in-situ" baking under ultra-high vacuum has been successfully applied by several laboratories to reduce those losses and …

Pulsed System For Optical Discharge Of Thin-Film Insulators, Jared Otterstrom, Ryan C. Hoffman, Jr Dennison

Senior Theses and Projects

Much research is being performed in order to characterize the charging of spacecraft materials. The importance and applications of this research is numerous and especially useful to the development of satellites¹. The USU Materials Physics group is currently performing research in this field related to electron emission for spacecraft materials¹. This includes testing sample material in an ultra high vacuum chamber. A problem encountered in this testing is that negative charge can build up on the sample material and modify the electron emission measurements². To remedy this problem, my senior project was to develop, …

Microscopic Theory Of The Low Frequency Raman Modes In Germanium Nanocrystals, Shang-Fen Ren, Peter Y. Yu

Faculty publications – Physics

We have studied the Raman intensities of low-frequency phonon modes in germanium (Ge) nanocrystals (NC) with varying sizes by using a microscopic valence force field model. The results are compared with the predictions of the continuum model of Lamb using a projection method. We found that the l=0 spheroidal Lamb modes are Raman active in the parallel polarization scattering geometry, while the l=2 spheroidal Lamb modes are active in the crossed polarization geometry. This result agrees with the group theory prediction that the torsional Lamb modes are not Raman active, but is in disagreement with the identification of torsional Lamb …

Crossover Energetics For Halogenated Si(100): Vacancy Line Defects, Dimer Vacancy Lines, And Atom Vacancy Lines, G. J. Xu, Nikolai A. Zarkevich, Abhishek Agrawal, A. W. Signore, B. R. Trenhaile, Duane D. Johnson, J. H. Weaver

Duane D. Johnson

We investigated surface patterning of I-Si(100)-(2×1) both experimentally and theoretically. Using scanning tunneling microscopy, we first examined I destabilization of Si(100)-(2×1) at near saturation. Dimer vacancies formed on the terraces at 600 K, and they grew into lines that were perpendicular to the dimer rows, termed vacancy line defects. These patterns were distinctive from those induced by Cl and Br under similar conditions since the latter formed atom and dimer vacancy lines that were parallel to the dimer rows. Using first-principles density functional theory, we determined the steric repulsive interactions associated with iodine and showed how the observed defect patterns …

Size-Driven Domain Reorientation In Hydrothermally Derived Lead Titanate Nanoparticles, Zhiyuan Ye, Elliot B. Slamovich, Alexander H. King

Alexander H. King

High-resolution transmission electron microscopy studies of hydrothermally derived platelike lead titanate nanoparticles reveal that below a critical size of approximately 70 nm, the single ferroelectric domain polarization axis reorients from perpendicular to parallel to the plate. We suggest that during particle growth, ions in the hydrothermal processing medium compensate for the ferroelectric depolarization energy. When the processing medium is removed by washing and drying, single domain nanoparticles minimize their depolarization energy by c-axis flipping.

Importance Of Thermal Disorder On The Properties Of Alloys: Origin Of Paramagnetism And Structural Anomalies In Bcc-Based Fe1−Xalx, Andrei V. Smirnov, W. A. Shelton, Duane D. Johnson

Duane D. Johnson

Fe1−xAlx exhibits interesting magnetic and anomalous structural properties as a function of composition and sample processing conditions arising from thermal or off-stoichiometric chemical disorder, and, although well studied, these properties are not understood. In stoichiometric B2 FeAl, including the effects of partial long-range order, i.e., thermal antisites, we find the experimentally observed paramagnetic response with nonzero local moments, in contrast to past investigations that find either a ferromagnetic or nonmagnetic state, both inconsistent with experiment. Moreover, from this magnetochemical coupling, we are able to determine the origins of the observed lattice constant anomalies found in Fe1−xAlx for x≃0.25–0.5 under various …

Specification Of Jecp/Holz, An Interactive Computer Program For Simulation Of Holz Pattern, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

1. Purpose of the program 2. Graphic user interface and program design 3. Formulas for calculating the positions of the HOLZ lines 4. System requirement 5. Installation and user instruction 6. How to contact the author 7. References

1. Purpose of the program JECP/HOLZ (Li, 2005a) is one computer program in the Java Electron Crystallography Package (JECP), which is designed and written by Dr. XingZhong Li. The package is developed for quantitative electron diffraction and image processing purpose, JECP/HOLZ is an interactive program for simulation of the higher-order Laue zone (HOLZ) lines using kinematical approximation and a first-order dynamic correction. …

Mechanism Of Structural Transformation In Bismuth Titanate, Sudhanshu Mallick, Keith J. Bowman, Alexander H. King

Alexander H. King

Sodium-doped bismuth titanate undergoes a transformation from Bi4Ti3O12 to Na0.5Bi4.5Ti4O15 on heating in air at temperatures exceeding 800 °C. This transformation proceeds through the intermediate Na0.5Bi8.5Ti7O27 structure which is an intergrowth phase of the two. High-resolution transmission electron microscopy was used to study this transformation. From the Moiré pattern that was obtained, the crystallographic orientation of the transformation front has been determined and a mechanism is proposed for this structural transformation.

Dislocation-Indenter Interaction In Nanoindentation, M. Ravi Shankar, Alexander H. King, Srinivasan Chandrasekar

Alexander H. King

A formulation of dislocation-indenter interaction in two-dimensional, isotropic elasticity is presented. A significant dislocation-indenter interaction is predicted when dislocations are nucleated very close to the indenter. This interaction is expected to have an important influence on dislocation motion and multiplication. Upon nucleation close to the indenter, the dislocations are shown to modify the load, load distribution, and moment acting on the indenter. This effect is seen to vary with the indentation contact length. Further away from the indenter, the indenter-dislocation interaction is shown to be negligible.

Boron-Rich Semiconducting Boron Carbide Neutron Detector, Andrew D. Harken, Ellen E. Day, Brian W. Robertson, Shireen Adenwalla

Shireen Adenwalla Papers

Data on the neutron detection capabilities of a variety of boron carbide/Si heterojunction diodes is presented. The pulse height spectra are compared with previously measured conversion layer devices and the variations in shape and position of the peaks are discussed.

Magnetic Moments And Adiabatic Magnetization Of Free Cobalt Clusters, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Walt A. De Heer

Xiaoshan Xu Papers

Magnetizations and magnetic moments of free cobalt clusters CoN (12< N <200) in a cryogenic (25 K ≤ T ≤ 100 K) molecular beam were determined from Stern-Gerlach deflections. All clusters preferentially deflect in the direction of the increasing field and the average magnetization resembles the Langevin function for all cluster sizes even at low temperatures. We demonstrate in the avoided crossing model that the average magnetization may result from adiabatic processes of rotating and vibrating clusters in the magnetic field and that spin relaxation is not involved. This resolves a longstanding problem in the interpretation of cluster beam deflection experiments with implications for nanomagnetic systems in …

The Effects Of Humidity On The Dielectric Response In Ferroelectric Polymer Films Made By Langmuir-Blodgett Deposition, Kristin L. Kraemer, Alexander V. Sorokin, Christina M. Othon, Stephen Ducharme, Vladimir M. Fridkin

Stephen Ducharme Publications

No abstract provided.

Investigation Of Ferroelectricity In Newly Synthesized Nitrile Polymer Systems, Matt Poulsen, Stephen Ducharme, Alexander V. Sorokin, Sahadeva Reddy, James M. Takacs, Y. Wen, Jihee Kim, Shireen Adenwalla

Stephen Ducharme Publications

The ferroelectric and piezoelectric properties of newly synthesized polymer systems have been studied. To date PVDF and its copolymers P(VDF-TrFE) have provided the bulk of the knowledge pertaining to ferroelectricity in polymers. Recently, ultrathin ferroelectric films of P(VDF-TrFE) 70:30 have been fabricated using the Langmuir-Blodgett technique [4]. In this study, various new polymers have been synthesized by chemically altering the PVDF structure. This alteration was performed in order to enhance the amphiphilic nature of the polymer and thus improve the LB film quality and control. Various chemical groups have been used to replace the electropositive hydrogen and electronegative fluorine found …

Measurement Of Magnetic Moments Of Free BiNMnM Clusters, Shuangye Yin, Xiaoshan Xu, Ramiro Moro, Walt A. De Heer

Xiaoshan Xu Papers

Magnetic properties of free Bi_NMn_M clusters (N=2–20, M=0–7) are determined from Stern-Gerlach deflections at low temperature (46.5 K). Pure bismuth clusters with odd number of atoms exhibit paramagnetic deflections. The addition of manganese atoms produces a ferromagnetic response which is strongly size dependent. Certain combinations have very large magnetic moments such as Bi₅Mn₃, Bi₉ Mn₄, Bi₁₀Mn₅, and Bi₁₂Mn₆.

Characterisation Of An Acrylamide-Based Photopolymer For Data Storage Utilizing Holographic Angular Multiplexing, Hosam Sherif, Izabela Naydenova, Suzanne Martin, Colm Mcginn, Vincent Toal

Articles

An acrylamide-based photopolymer formulated in the Centre for Industrial and Engineering Optics has been investigated with a view to further optimisation for holographic optical storage. Series of 18 to 30 gratings were angularly multiplexed in a volume of photopolymer layer at a spatial frequency of 1500 lines/mm. Since the photopolymer is a saturable material, an exposure scheduling method was used to exploit the entire dynamic range of the material and allow equal strength holographic gratings to be recorded. This investigation yielded the photopolymer M/# for moderately thin layers. Photopolymer temporal stability was also studied by measuring variations of material shrinkage, …

Nuclear Magnetic Resonance Studies Of Relaxor Ferroelectrics, William J. Brouwer

Dissertations, Theses, and Masters Projects

This work is devoted to the study of local order in the ferroelectric PbSc1/2Ta1/2O3 (PST) and relaxor ferroelectric solid solutions (1-x)PbSC2/3W1/3O3-(x)PbTiO 3 (PSW-PT), (1x)PbSC2/3W1/3O3-(x)PbZrO 3 (PSW-PZ). Novel Magic Angle Spinning (MAS) Solid State Nuclear Magnetic Resonance (SS-NMR) experiments, including Multiple Quantum MAS (MQMAS) and Double Quantum Filtered Satellite Transition (DQF-STMAS), have been performed on these materials. A gamma function model is proposed for the distribution of quadrupole coupling constants, based on the Poissonian nature of atomic displacements. Moments for distributions may be subsequently extracted through agreement between experimental spectra and simulations implemented in novel programs. Simple crystal compound scandium oxide …

Condensation On (002) Graphite Of Liquid Bismuth Far Below Its Bulk Melting Point, M. K. Zayed, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Condensation of thermally evaporated Bi on (002) graphite, at temperatures of 300-523K, was studied using in situ reflection high-energy electron diffraction (RHEED) and room temperature ex situ atomic force microscopy (AFM). For deposition at temperatures below 415±5K, transmission RHEED patterns of Bi appeared at an average thickness of ∼0.5 monolayer (ML). AFM images showed that the film consisted of crystallites in the shape of triangular step pyramids with step heights corresponding to single and double Bi layers in the [111] direction. This morphology indicates crystallization from the vapor. For deposition at higher temperatures, diffuse RHEED patterns appeared independent of the …

Quantum Monte Carlo Method For Boson Ground States: Application To Trapped Bosons With Attractive And Repulsive Interactions, Wirawan Purwanto

Dissertations, Theses, and Masters Projects

We formulate a quantum Monte Carlo (QMC) method for calculating the ground state of many-boson systems. The method is based on a field-theoretical approach, and is closely related to existing fermion auxiliary-field QMC methods which are applied in several fields of physics. The ground-state projection is implemented as a branching random walk in the space of permanents consisting of identical single-particle orbitals. Any single-particle basis can be used, and the method is in principle exact. We apply this method to an atomic Bose gas, where the atoms interact via an attractive or repulsive contact two-body potential parametrized by the s-wave …

Vibrational Lifetimes Of Hydrogen And Oxygen Defects In Semiconductors, Baozhou Sun

Dissertations, Theses, and Masters Projects

Characterization of defect and impurity reactions, dissociation, and migration in semiconductors requires a detailed understanding of the rates and pathways of vibrational energy flow and of the coupling mechanisms between local modes and the phonon bath of the host material. Information on the inelastic microscopic interaction can be obtained by measuring the lifetime of local vibrational modes. This dissertation presents lifetime measurements of hydrogen and oxygen defects in semiconductors by means of time-resolved infrared pump-probe spectroscopy.;First, we measured the vibrational lifetime of H- and D-related bending modes in Si and other semiconductors. Time-resolved pump-probe and linewidth measurements reveal that the …

Monte Carlo Simulations Of Ferroelectric Crystal Growth And Molecular Electronic Structure Of Atoms And Molecules, Malliga Suewattana

Dissertations, Theses, and Masters Projects

In this thesis, we explore two stochastic techniques to study properties of materials in realistic systems. Specifically, the kinetic Monte Carlo (KMC) method is utilized to study the crystal growth process of ferroelectric materials and the quantum Monte Carlo (QMC) approach is used to investigate the ground state properties of atoms and molecules.;In the growth simulations, we study the growth rates and chemical ordering of ferroelectric alloys using an electrostatic model with long-range Coulomb interactions. Crystal growth is characterized by thermodynamic processes involving adsorption and evaporation, with solid-on-solid restrictions and excluding diffusion. A KMC algorithm is formulated to simulate this …

Impact Of Large Scale Substrate Roughness On Giant Magnetoresistive Thin Films, Shannon M. Watson

Dissertations, Theses, and Masters Projects

This dissertation presents an investigation on the effects of large scale roughness on the properties of giant magnetoresistive multilayers. The large scale roughness (sigmarms > 5 nm) is introduced into giant magnetoresistive thin films through the substrate. Current-in-plane (CIP) and current-perpendicular-to-the-plane (CPP) thin films were deposited by dc magnetron and triode sputtering. All films were characterized for roughness, magnetic and electronic behavior.;Our research on both pseudo spin valves and exchange-biased spin valves shows that long length scale roughness does not have a significant detrimental effect on GMR thin films. For the CIP films, we find that a decrease in GMR correlates …

Spatially Heterogeneous Dynamics And The Adam-Gibbs Relation In The Dzugutov Liquid, Yeshitela Gebremichael, M Vogel, M Bergroth, Francis W. Starr, Sharon C. Glotzer

Francis Starr

No abstract provided.