Physics Commons^™

Imaging And Engineering The Nanoscale-Domain Structure Of A Sr0.61Ba0.39Nb2O6 Crystal Using A Scanning Force Microscope, K. Terabe, S. Takekawa, M. Nakamura, K. Kitamura, Alexei Gruverman

Alexei Gruverman Publications

We have investigated the ferroelectric domain structure formed in a Sr_0.61Ba_0.39Nb₂O₆ single crystal by cooling the crystal through the Curie point. Imaging the etched surface structure using a scanning force microscope (SFM) in both the topographic mode and the piezoresponse mode revealed that a multidomain structure of nanoscale island-like domains was formed. The island-like domains could be inverted by applying an appropriate voltage using a conductive SFM tip. Furthermore, a nanoscale periodically inverted-domain structure was artificially fabricated using the crystal which underwent poling treatment.

Nanoscale Observation Of Photo-Induced Domain Pinning And Investigation Of Imprint Behavior In Ferroelectric Thin Films, Alexei Gruverman, B. J. Rodriguez, R. J. Nemanich, A. I. Kingon

Alexei Gruverman Publications

Piezoresponse force microscopy has been used to investigate the nanoscale mechanism of imprint behavior of ferroelectric PbTiO₃ thin films by studying the photoinduced changes in the hysteresis loops of individual grains. Illumination of the film with UV light resulted in a voltage shift opposite to that observed in ferroelectric thin film capacitors. This effect is attributed to the generation of an electric field within the surface dielectric layer as a result of the interaction between photo-induced charges and polarization charges. Application of a small non-switching bias to the film with simultaneous UV illumination resulted in domain pinning in …

Effect Of Grain Growth Inhibitors On The Hysteresis Properties Of Nd10Fe82C6B2Melt-Spun Alloys, M. Daniil, Y. Zhang, H. Okumura, George C. Hadjipanayis, David J. Sellmyer

David Sellmyer Publications

An effort has been made to improve the coercivity of nanocomposite Nd₁₀Fe₈₂C₆B₂ alloys, using small amounts (up to 1 at%) of Cr, Ti, Nb, Zr, and Ga. X-ray studies revealed that the amount of –Fe phase in both as-spun and annealed ribbons was significantly reduced for Nb and Zr substitutions, but increased for all the other substitutions. From the magnetic properties point of view, Zr (1 at%) was proven to be the most advantageous of all, since it increased the coercivity of annealed ribbons from 3.2 to 4.8 kOe and the maximum energy …

Diffusion Based Grating Formation In A Photopolymer Material, Justin R. Lawrence

Masters

Photopolymers are promising materials for use in holography. They have many advantages such as ease of use and are capable of efficiencies of up to 100%. However, the main disadvantage to these materials is their inability to record high spatial frequency gratings when compared to other materials such as dichromated gelatine and silver halide emulsion. This poor spatial frequency response is not predicted by any of the current physical modes. In this study, it is proposed that this effect is due to polymer chains growing away from their initiation point and causing a ‘smearing’ of the profile to be recorded. …

Seedlayer And Preheating Effects On Crystallography And Recording Performance Of Cocrptb Perpendicular Media, Min Zheng, Geon Choe, Kenneth E. Johnson, Lan Gao, Sy_Hwang Liou

Department of Physics and Astronomy: Faculty Publications

The effects of seedlayer (SL) and preheating on the crystallographic, magnetic, and recording properties of CoCr₁₈Pt₁₆B₄ granular perpendicular magnetic media have been investigated. For the media with Ru as underlayer, although higher preheating improves both coercivity and squareness, the media is much noisier. With introducing Ta SL, Ru (0002)/Co (0002) crystallography is greatly enhanced. High coercivity, unity squareness, and negative nucleation field are achieved even at low preheating without degrading signal-to-noise ratio. In addition, the media is magnetically stable for a wide range of recording density.

Permanent-Magnet Properties Of Thermally Processed Fept And Fept–Fe Multilayer Films, Jian Zhou, Ralph Skomski, Xingzhong Li, Wei Tang, George C. Hadjipanayis, David J. Sellmyer

David Sellmyer Publications

FePt single-layer and FePt–Fe multilayer thin films are prepared by magnetron sputtering. By varying the Pt content, FePt, Fe₃Pt, or a mixture of FePt and Fe₃Pt can be obtained in Fe–Pt single layers. In annealed FePt–Fe multilayers, the coercivities decrease with the introduction of Fe layers compared to FePt single layers, while the magnetization increases. The single-phase behavior of the hysteresis loops of FePt–Fe multilayers indicates the existence of exchange coupling in these materials. For one FePt–Fe sample with optimized exchange coupling, the intrinsic properties correspond to an energy product of 19 MGOe. The texture of …

Characterization Of Homoepitaxial P-Type Zno Grown By Molecular Beam Epitaxy, David C. Look, D. C. Reynolds, C. W. Litton, R. L. Jones, D. B. Eason, G. Cantwell

Physics Faculty Publications

An N-doped, p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating ZnO substrate. Hall-effect and conductivity measurements on the layer give: resistivity = 4×10¹ Ω cm; hole mobility = 2 cm²/V s; and hole concentration = 9×10¹⁶ cm⁻³. Photoluminescence measurements in this N-doped layer show a much stronger peak near 3.32 eV (probably due to neutral acceptor bound excitons), than at 3.36 eV (neutral donor bound excitons), whereas the opposite is true in undoped ZnO. Calibrated, secondary-ion mass spectroscopy measurements show an N surface concentration of about …

Representation Of A Quantum Ensemble As A Minimal Set Of Pure States, Thomas E. Skinner, Steffen J. Glaser

Physics Faculty Publications

The density matrix ρ for an n-level system is decomposed into the minimum number of pure states necessary to calculate physical observables. The corresponding physical system is first represented by a set B of n pure states |β_i〉, together with their statistical weights. The time evolution of the system is therefore calculated as B(t)=UB(t₀), with the propagator U operating on each member of the set, in contrast to the more laborious ρ(t)=Uρ(t₀)U^†. At least one of the states can be eliminated from the set by reducing its weight to zero via a …

Normal Mode Mixing And Ferromagnetic Resonance Linewidth, Andrew Kunz, R. D. Mcmichael

Physics Faculty Research and Publications

The normal modes of an inhomogeneous thin film are obtained by diagonalization of the perturbed Hamiltonian. The resulting modes are mixtures of the spin-wave modes and the uniform mode. We find that the ferromagnetic resonance intensity spectrum of the diagonalized system has a Lorentzian profile, and that the results correspond to the two-magnon model for weak perturbations. For stronger perturbations, the density of states is smoothed, and the spectrum becomes asymmetric due to the low-frequency cutoff of the spin-wave manifold. The technique is expected to be valid for perturbation amplitudes that are large enough to invalidate the assumptions of the …

Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

Physics Faculty Research & Creative Works

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk, boundary conformal correlators have a …

Branching Ratio Measurements Of Exclusive B+ Decays To Charmonium With The Collider Detector At Fermilab, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on measurements of the branching ratios of the decays B+→χc10 (1P)K+ and B+→J/ψK+π+π-, where χc10(1P)→J/ψγ and J/ψ→μ+μ- in pp̅ collisions at √s=1.8 TeV. Using a data sample from an integrated luminosity of 110 pb-1 collected by the Collider Detector at Fermilab we measure the branching ratios to be BR(B+→ χc10(1P)K+)=15.5±5.4(stat)±1.5(syst)±1.3(br)×10-4 and BR(B+→J/ψK+π+π-)=6.9±1.8(stat)±1.1(syst)±0.4(br)×10-4 where (br) is due …

Adaptive Harmonic Balance Method For Unsteady, Nonlinear, One-Dimensional Periodic Flows, Raymond C. Maple

Theses and Dissertations

A new adaptive split-domain harmonic balance computational fluid dynamics (CFD) method is developed to solve highly nonlinear time-periodic flows such as those found in turbomachinery. The basic harmonic balance CFD method transforms an unsteady time-periodic problem into a steady-state problem by assuming a solution in the form of a Fourier series in time. The new method employs a unique multi-domain split-operator solution technique to remove a large-series stability restriction present in previous harmonic balance CFD approaches. In addition, the new method adapts the frequency content to the flow, starting with a small number of Fourier frequencies and augmenting the frequency …

High Energy Laser Pointing Through Extended Turbulence, Jason A. Tellez

Theses and Dissertations

The airborne laser (ABL) uses adaptive optics to compensate the atmospheric turbulence between the ABL and the target. The primary purpose of this compensation is to increase the energy density of the energy laser at the target. However, the specifics of the engagement scenario require the tracking point of reference and the adaptive optics point of reference to be located at different points on the target. This research considers the effects of tracking a target in one direction while compensating for atmospheric turbulence in a different directions. The target references used are a point source and a rectangle, while a …

Holographic Analysis Of Diffraction Structure Factors, S. Marchesini, N. Mannella, C. S. Fadley, M. A. Van Hove, J. J. Bucher, D. K. Shuh, L. Fabris, M. J. Press, M. W. West, Wayne C. Stolte, Z. Hussain

Chemistry and Biochemistry Faculty Research

We combine the theory of inside-source/inside-detector x-ray fluorescence holography and Kossel lines/x ray standing waves in kinematic approximation to directly obtain the phases of the diffraction structure factors. The influence of Kossel lines and standing waves on holography is also discussed. We obtain partial phase determination from experimental data obtaining the sign of the real part of the structure factor for several reciprocal lattice vectors of a vanadium crystal.

Discovery Of A Substellar Companion To The K2 Iii Giant Ɩ Draconis, Sabine Frink, David Mitchell, Andreas Quirrenbach, Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler

Physics

We report precise radial velocity measurements of the K giant ɩ Dra (HD 137759, HR 5744, HIP 75458), carried out at Lick Observatory, which reveal the presence of a substellar companion orbiting the primary star. A Keplerian fit to the data yields an orbital period of about 536 days and an eccentricity of 0.70. Assuming a mass of 1.05 M8 for ɩ Dra, the mass function implies a minimum companion mass m₂ sin i of 8.9 M_J, making it a planet candidate. The corresponding semimajor axis is 1.3 AU. The nondetection of the orbital motion by Hipparcos …

Resonances Of Periodic Metal-Dielectric Structures At The Infrared Wavelength Region, Oren Sternberg

Dissertations

Metal meshes have been used as reflectors in radar receivers for wavelength much longer than the periodic constant of the conducting wires and as optical reflectors in a FabryPerot in the far infrared. Cross shaped metal meshes can be used as band pass filters but the design theory and near field properties have not been known.

Transmittance of thin, single-layer and multiplayer metal meshes has been investigated using Micro-Strips, yielding numerical solutions of Maxwell's equations. The near field effect was studied for two alignment configurations of cross shaped metal meshes, both free standing and with dielectrics, and transmission line theory …

Radiation Transport Modeling Of Beam-Target Experiments For The Aaa Project: Quaterly Report, June 01- August 31, 2002, William Culbreth

Reactor Campaign (TRP)

The national development of technology to transmute nuclear waste depends upon the generation of high-energy neutrons produced by proton spallation. Proton accelerators, such as LANSCE at the Los Alamos National Laboratory, are capable of producing 800 MeV protons. By bombarding a lead /bismuth target, each proton may generate up to 25 neutrons that can activate fission of transuranic isotopes. Students at UNLV have been involved in radiation transport calculations in collaboration with researchers at the Los Alamos National Laboratory and at the Argonne National Laboratory.

Direct Measurement Of The W Boson Decay Width, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

Based on 85 pb^-1 data of pp̅ collisions at √s = 1.8 TeV collected using the DØ detector at Fermilab during the 1994–1995 run of the Tevatron, we present a direct measurement of the total decay width of the W boson Γ_W . The width is determined from the transverse mass spectrum in the W→e+ν _ℯ decay channel and found to be Γ_W=2.23_-0.14^+0.15 (stat) ±0.10(syst) GeV, consistent with the expectation from the standard model.

Boron-Carbide And Boron Rich Rhobohedral Based Transistors And Tunnel Diodes, Peter A. Dowben

Peter Dowben Publications

The present invention relates to the fabrication of a boron carbide/boron semiconductor devices. The results suggest that with respect to the approximately 2 eV band gap pure boron material, 0.9 eV band gap boron carbide (B₅C) acts as a p-type material. Both boron and boron carbide (B₅C) thin films were fabricated from single source borane cage molecules using plasma enhanced chemical vapor deposition (PECVD). Epitaxial growth does not appear to be a requirement. We have doped boron carbide grown by plasma enhanced chemical vapor deposition. The source gas close- 1,2-dicarbadecaborane (orthocarborane) was used to grow the …

Dielectric Properties Of A Ferroelectric Copolymer Langmuir–Blodgett Film, Mahantappa S. Jogad, Stephen Ducharme

Stephen Ducharme Publications

We report measurements of the real (epsilon prime) and imaginary (epsilon double-prime) parts of the relative complex permittivity of a Langmuir–Blodgett film of ferroelectric copolymer of vinylidene fluoride (70%) with trifluoroethylene (30%). The measurements were made in the temperature range of 35 to 125° C, and frequency range of 19 Hz to 5 MHz. The results indicate low frequency loss due to conduction and dielectric loss peak near the ferroelectric–paraelectric phase transition.

Temperature Variations From Hubble Space Telescope Imagery And Spectroscopy Of Ngc 7009, R. H. Rubin, N. J. Bhatt, R. J. Dufour, B. A. Buckalew, M. J. Barlow, X.-W. Liu, P. J. Storey, B. Balick, Gary J. Ferland, J. P. Harrington, P. G. Martin

Physics and Astronomy Faculty Publications

We present new Hubble Space Telescope (HST)/WFPC2 imagery and STIS long-slit spectroscopy of the planetary nebula NGC 7009. The primary goal was to obtain high spatial resolution of the intrinsic line ratio [O III] 4364/5008 and thereby evaluate the electron temperature (T_e) and the fractional mean-square T_e variation (t_A²)across the nebula. The WFPC2 T_emap is rather uniform; almost all values are between 9000–11 000 K, with the higher T_e values closely coinciding with the inner He⁺⁺ zone. The results indicate very small values–≲0.01– for …

Leading Neutron Production In E+ P Collisions At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan

Faculty Publications

The production of neutrons carrying at least 20% of the proton beam energy (xL > 0.2) in e+ p collisions has been studied with the ZEUS detector at HERA for a wide range of Q2, the photon virtuality, from photoproduction to deep inelastic scattering. The neutron-tagged cross section, ep → e′ Xn, is measured relative to the inclusive cross section, ep → e′ X, thereby reducing the systematic uncertainties. For xL > 0.3, the rate of neutrons in photoproduction is about half of that measured in hadroproduction, which constitutes a clear breaking of factorisation. There is about a 20% rise in the …

Design And Analysis For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides: Quarterly Progress Report 5/16/02- 8/15/02, Yitung Chen, Randy Clarksean, Darrell Pepper

Fuels Campaign (TRP)

An important aspect of the Advanced Accelerator Applications (AAA) program is the development of a casting process by which volatile actinide element (i.e., americium) can be incorporated into metallic alloy fuel pins. The traditional metal fuel casting process uses an inductively heated crucible.

This process works well for the fabrication of metal fuel pins traditionally composed of alloys of uranium and plutonium, but does not work well when highly volatile actinides are included in the melt. The problem occurs both during the extended time period required to superheat the alloy melt as well as when the chamber must be evacuated. …

Scaling, Domains, And States In The Four-Dimensional Random Field Ising Magnet, Alan Middleton

Physics - All Scholarship

The four dimensional Gaussian random field Ising magnet is investigated numerically at zero temperature, using samples up to size $64^4$, to test scaling theories and to investigate the nature of domain walls and the thermodynamic limit. As the magnetization exponent $\beta$ is more easily distinguishable from zero in four dimensions than in three dimensions, these results provide a useful test of conventional scaling theories. Results are presented for the critical behavior of the heat capacity, magnetization, and stiffness. The fractal dimensions of the domain walls at criticality are estimated. A notable difference from three dimensions is the structure of the …

Spin Injection Into Amorphous Semiconductors, Evgeny Y. Tsymbal, V. M. Burlakov, Ivan I. Oleinik

Evgeny Tsymbal Publications

Using a realistic model for the atomic and electronic structure of amorphous silicon, we explore spin injection into amorphous semiconductors. We calculate the spin-dependent conductance of magnetoresistive devices within the Landauer-Büttiker formalism including inelastic scattering. We find that reducing the density of injected carriers and increasing the spin polarization of the electrodes are favorable for spin injection, whereas inelastic scattering is detrimental, and show that the upper limit for magnetoresistance is given by Julliere's formula.

Poiseuille Advection Of Chemical Reaction Fronts, Boyd F. Edwards

All Physics Faculty Publications

Poiseuille flow between parallel plates alters the shapes and velocities of chemical reaction fronts. In the narrow-gap limit, the cubic reaction-diffusion-advection equation predicts a front-velocity correction equal to the gap-averaged fluid velocity ϵ. In the singular wide-gap limit, the correction equals the midgap fluid velocity 3ϵ/2 when the flow is in the direction of propagation of the reaction front, and equals zero for adverse flow of any amplitude for which the front has a midgap cusp. Stationary fronts are possible only for adverse flow and finite gaps. Experiments are suggested.

Construction And Testing Of A Low-Finesse Fabry-Perot Interferometer For Use In Atomic Spectroscopy, Nathan C. Moody

Student Works

I built a low-finesse confocal cavity with aluminum mirrors for use in the imaging of ultra-cold calcium ion plasmas. The confocal cavity provides stability at large mirror separations, a condition necessary for achieving both low finesse and narrow peak widths. Additionally, the finesse in the case of coherent input is effectively doubled compared to multi-mode resonance. The cavity was tested using a GaN diode laser input at 397nm. The transmission obtained indicated that the finesse of the cavity was slightly lower than the prediction based on measurements of the mirror reflectivities and the assumption of incoherent input.

Simple, Compact Source For Low-Temperature Air Plasmas, D. P. Sheehan, J. Lawson, M. Sosa, R. A. Long

Physics and Biophysics: Faculty Scholarship

A simple, compact source of low-temperature, spatially and temporally uniform air plasma using a Telsa induction coil driver is described. The low-power ionization discharge plasma is localized (2 cm X 0.5 cm X 0.1 cm) and essentially free of arc channels. A Teflon coated rolling cylindrical electrode and dielectric coated ground plate are essential to the source’s operation and allow flat test samples to be readily exposed to the plasma. The plasma is a copious source of ozone and nitrogen oxides. Its effects on various microbes are discussed.

Magnetism Of Co Nanocluster Films, Y. Qiang, R.F. Sabiryanov, Sitaram Jaswal, Yi Liu, H. Haberland, David J. Sellmyer

David Sellmyer Publications

A cluster-beam technique is used to produce nearly monodispersed nanoclusters of Co while independently varying their size and concentration. The Co clusters are embedded in Cu and SiO₂ to form films with cluster size varying from 300 to 9000 atoms and Co concentration varying from 10 to 50 vol %. The Co magnetization (M_s) increases with increasing cluster size and decreases with increasing Co concentration for a given cluster size but is always less than the bulk value. First-principles calculations are used to analyze the experimental data in terms of the local environment effects at the …

Corrosion Of Steel By Lead Bismuth Eutectic: Quarterly Report For May-June-July 2002, John Farley

Transmutation Sciences Materials (TRP)

The goal of this project is to understand the basic science of corrosion in the steel/LBE system.

We are taking more data, typically using the newly installed X-ray Photoelectron Spectrometry (XPS) apparatus, and analyzing our existing data. Undergraduate students Denise Parsons and Julia Manzerova have helped a great deal in the analysis of the data. We can obtain the elemental composition as a function of position within the sample. This gives clues to the migration of materials, the composition of the protective oxide layer, and the basic science of the corrosion process. We found dramatic differences between the exposed and …