Physical Sciences and Mathematics Commons^™

Thickness Dependence Of Magneto-Transport In Cu-Co Granular Thin Films, Jian Qing Wang, Ngocnga Dao, Ham H. Kim, Scott L. Whittenburg

Chemistry and Biochemistry Faculty Publications

This work explores the thickness dependence of magneto-transport properties in granular thin films with different thickness. These results are compared with silver-based film series studied earlier. It was observed that the thickness dependence of the GMReffect was sensitive to the surface chemistry of the films. The extraordinary Hall effect (EHE) in these films was measured and found to be different from the Ag-based system. In the Cu-based system, the EHE is a weak function of film thickness over the range studied. When the variation of the spontaneous magnetization is taken into account the effective EHE has a universal thickness dependence

Interactions And Switching Behavior Of Anisotropic Magnetic Dots, Kory D. Sorge, Arti Kashyap, Ralph Skomski, Lanping Yue, L. Gao, Roger D. Kirby, Sy_Hwang Liou, David J. Sellmyer

Roger Kirby Publications

The magnetic properties of collections of three soft magnetic nanodots with various aspect ratios are investigated. Permalloy films are first produced by dc magnetron sputtering. Focused ion beam milling is then used to mill dots, each with different shape anisotropy. We find that each of the three dots in the system has a unique switching field, and that there is significant magnetostatic coupling. Micromagnetic simulations suggest that for dot separations of less than 50 nm there exists strong interdot interaction, leading to the possibility of controlled switching of neighboring dots. This switching behavior is of interest in magnetic information processing.

Search For New Particles In The Two-Jet Decay Channel With The Dø Detector, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present the results of a search for the production of new particles decaying into two jets in p̅p collisions at √s =1.8 TeV, using the DØ 1992–1995 data set corresponding to 109 pb^-1. We exclude at the 95% confidence level the production of excited quarks (q^*) with masses below 775 GeV/c², the most restrictive limit to date. We also exclude standard-model-like W′ (Z′) bosons with masses between 300 and 800 GeV/c² (400 and 640 GeV/c²). A W8 boson with mass ,786 GeV/ …

New Limits On The Drift Of Fundamental Constants From Laboratory Measurements, Marc P. Fischer, Nikolai N. Kolachevsky, Marcus Zimmermann, Ronald Holzwarth, Th H. Udem, Theodor Wolfgang Hansch, Michel Abgrall, Jan Grunert, Ivan Maksimovic, Sebastien Bize, Harold Marion, Franck Pereira M Dos Santos, Pierre Lemonde, Giorgio Santarelli, Ph Laurent, Andre Clairon, Christophe Salomon, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We have remeasured the absolute 1S-2S transition frequency ν_H in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (-29 ± 57) Hz for the drift of ν_H with respect to the ground state hyperfine splitting ν_Cs in ¹³³Cs. Combining this result with the recently published optical transition frequency in ¹⁹⁹Hg⁺ against ν_Cs and a microwave ⁸⁷Rb and ¹³³Cs clock comparison, we deduce separate limits on α˙ / α = (-0.9 &plusm; 2.9) x 10^-15 yr^-1 and the fractional time …

Electron Self-Energy For Higher Excited S Levels, Ulrich D. Jentschura, Peter J. Mohr

Physics Faculty Research & Creative Works

A nonperturbative numerical evaluation of the one-photon electron self-energy for the 3S and 4S states with charge numbers Z=1 to 5 is described. The numerical results are in agreement with known terms in the expansion of the self-energy in powers of Zα.

Magnetic Nanotubes Produced By Hydrogen Reduction, Yucheng Sui, Ralph Skomski, Kory D. Sorge, David J. Sellmyer

David Sellmyer Publications

FePt and Fe₃O₄ nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometry. Loading the templates with an Fe chloride and Pt chloride mixture, followed by hydrogen reduction at 560 °C, leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. An Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe₃O₄ tubes. The versatility of the method indicates that materials with a wide range of …

Magnetism Of L10 Compounds With The Composition Mt (M = Rh, Pd, Pt, Ir And T = Mn, Fe, Co, Ni), Arti Kashyap, Ralph Skomski, Ashok K. Solanki, Yinfan Xu, David J. Sellmyer

David Sellmyer Publications

The electronic band structure of ordered equiatomic compounds of 3d transition elements (Mn, Fe, Co, Ni) with nonmagnetic 4d and 5d elements (Rh, Pd, Pt, Ir) are investigated by linear muffin-tin orbital calculations. The systematic study considers 3d and 4d/5d spin moments and interatomic exchange interactions, with emphasis on the comparison between ferromagnetic and antiferromagnetic order. Total and site-resolved exchange interactions are calculated from first principles, and the obtained exchange constants are used to estimate ordering temperatures on a mean-field level.

Effect Of Au Spacer Layer On L10 Phase Ordering Temperature Of Copt Thin Films, T. Yokota, L. Gao, Sy_Hwang Liou, M.L. Yan, David J. Sellmyer

Sy-Hwang Liou Publications

We have studied the effect of Au on the ordering temperature of CoPt films. The coercivity of the CoPt multilayer with 2 nm Au inserted is around 5 kOe after annealing at 400 °C. This ordering temperature is about 200 °C lower than that of a pure CoPt film. Crystallographical analysis using x-ray diffraction has also revealed that the lattice constant is drastically changed around the same temperature, which is related to the formation of the L1₀-ordered structure. Thus, the Au plays an important role in reducing the ordering temperature.

A Study Of Magnetic Interactions Of Ni80Fe20 Arrays Using Ultrasensitive Microcantilever Torque Magnetometry, L. Gao, D.Q. Feng, Lu Yuan, T. Yokota, Renat F. Sabirianov, Sy_Hwang Liou, M.D. Chabot, D. Porpora, J. Moreland

Sy-Hwang Liou Publications

We have successfully fabricated single and paired 300 nm×1.5 µm×32 nm Ni₈₀Fe₂₀ bars on a microcantilever using focused ion beam milling. Magnetic interactions of the paired bars were studied by using magnetic force microscopy, microcantilever torque magnetometry, and micromagnetic simulation. Our results clearly indicate that the magnetic switching behavior of the paired Ni₈₀Fe₂₀ bars is affected by magnetostatic interactions. The magnetic hysteresis curves for a sample with eight pairs of Ni₈₀Fe₂₀ bars consist of a series of stable switching states that are related to the domain wall motion in the bars.

Kapitza-Dirac Diffraction Without Standing Waves: Diffraction Without A Grating?, Olga Smirnova, Daniel L. Freimund, Herman Batelaan, Misha Ivanov

Department of Physics and Astronomy: Faculty Publications

We discuss electron diffraction from two counterpropagating light waves with two different frequencies.We show that, even though these waves do not form a standing wave, electron diffraction similar to the conventional Kapitza-Dirac effect, i.e., scattering on a standing wave, is still possible. The nonlinear response of the electron to the laser fields creates a stationary diffraction grating from which the same electron scatters.

Close-Coupling And Distorted-Wave Calculations For Electron-Impact Excitation Of The (5p⁵6p) States Of Xenon, K. Bartschat, Anand Dasgupta, Don H. Madison

Physics Faculty Research & Creative Works

We report on a series of calculations for electron-impact excitation of the (5p56p) states in xenon from the ground state (5p6)1S0 . As in previous calculations for other noble-gas targets, we find strong evidence of channel coupling for all incident energies considered (between threshold and 200 eV ). Although qualitative agreement with the experimental results of Fons and Lin [Phys. Rev. A 58, 4603 (1998)] is achieved, severe quantitative discrepancies of sometimes more than a factor of 2 remain.

Simulations Of Ferroelectric Polymer Film Polarization: The Role Of Dipole Interactions, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, John R. Hardy, Stephen Ducharme, Peter A. Dowben

Physics Faculty Publications

We present a systematic study of the dipole alignment in the polyvinylidene fluoride (PVDF) films using first-principles total energy calculations. The ground state of a single layer film is a state with all the dipoles lying parallel to the film plane. This can also be explained by a dipole-dipole interaction model. The induced mirror charges on conducting substrates or substrates with a non-negligible dielectric response play an important role in aligning the polarization perpendicular to the film. From fitting the ab initio calculations, we obtain an effective monomer dipole moment of 4.7 x 10⁻³⁰ C m. This corresponds to …

Microscopic Investigation Of Phonon Modes In Sige Alloy Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu

Faculty publications – Physics

Phonon modes in spherical silicon germanium alloy (SiGe) nanocrystals containing up to 1147 atoms (3.6 nm) have been investigated as a function of the Si concentration. Microscopic details of phonon modes, including phonon frequencies and vibrational amplitudes, phonon density-of-states are calculated directly from the dynamic matrices. In particular, the dependence of phonon frequency on the configuration (such as a different ratio of Si to Ge atoms), and location (surface or interior) of clusters of atoms in SiGe alloy nanocrystals have been investigated. Low frequency surface phonons that are related to the spheroidal and torsional modes of a continuum sphere are …

Classroom Demonstrations: Learning Tools Or Entertainment?, Catherine Hirshfeld Crouch, A. P. Fagen, J. P. Callan, E. Mazur

Physics & Astronomy Faculty Works

We compared student learning from different modes of presenting classroom demonstrations to determine how much students learn from traditionally presented demonstrations, and whether learning can be enhanced by simply changing the mode of presentation to increase student engagement. We find that students who passively observe demonstrations understand the underlying concepts no better than students who do not see the demonstration at all, in agreement with previous studies. Learning is enhanced, however, by increasing student engagement; students who predict the demonstration outcome before seeing it, however, display significantly greater understanding.

Nearest-Neighbor-Atom Core-Hole Transfer In Isolated Molecules, Renaud Guillemin, Oliver Hemmers, D. Rolles, S. W. Yu, A. Wolska, I. Tran, A. C. Hudson, J. Baker, Dennis W. Lindle

Environmental Studies Faculty Publications

A new phenomenon sensitive only to next-door-neighbor atoms in isolated molecules is demonstrated using angle-resolved photoemission of site-selective core electrons. Evidence for this interatomic core-to-core electron interaction is observable only by measuring nondipolar angular distributions of photoelectrons. In essence, the phenomenon acts as a very fine atomic-scale sensor of nearest-neighbor elemental identity.

Afci Quarterly Input – Unlv April Through June, 2004, Harry Reid Center For Environmental Studies. Nuclear Science And Technology Division

Transmutation Research Program Reports (TRP)

Quarterly report highlighting research projects and objectives of the Transmutation Research Program at the Nuclear Science & Technology Division, Harry Reid Research Center.

The University of Nevada, Las Vegas supports the AFCI through research and development of technologies for economic and environmentally sound refinement of spent nuclear fuel. The UNLV program has four components: infrastructure, international collaboration, student-based research, and management and program support.

Tidal Modulation Of The Gravitywave Momentum Flux In The Antarctic Mesosphere, P. J. Espy, G. O.L. Jones, G. R. Swenson, J. Tang, Michael J. Taylor

All Physics Faculty Publications

Airglow imager and dynasonde/IDI radar wind measurements at Halley Station, Antarctica (76S, 27W) have been used to estimate the diurnal variation of the vertical fluxes of horizontal momentum carried by highfrequency atmospheric gravity waves. The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from the sodium airglow imager data collected during four consecutive nights of near total darkness during July of 2000. These were combined with wind-velocity variances from coincident radar measurements to estimate the upper limit of the vertical flux of horizontal momentum during three-hour intervals throughout the period. The resulting momentum flux showed a marked …

Gravitational Energy Loss In High Energy Particle Collisions: Ultrarelativistic Plunge Into A Multidimensional Black Hole, Emanuele Berti, Marco Cavaglia, Leonardo Gualtieri

Physics Faculty Research & Creative Works

We investigate the gravitational energy emission of an ultrarelativistic particle radially falling into a D-dimensional black hole. We numerically integrate the equations describing black hole gravitational perturbations and obtain the energy spectra, total energy, and angular distribution of the emitted gravitational radiation. The black hole quasinormal modes for scalar, vector, and tensor perturbations are computed in the WKB approximation. We discuss our results in the context of black hole production at the TeV scale.

Inelastic X-Ray Scattering Studies In Lithium And Metal Ammonia Solutions, Ayman Hasan Said

Dissertations

In this work, inelastic x-ray scattering was used to measure the ionic collective excitations of a metal-ammonia system and the atomic form factor of lithium in a single crystal. For lithium and sodium ammonia systems, the measurements were carried out for different metal concentrations (lithium-ammonia with 2 0 , 16, and 13 mole percent metal [MPM] at T'=240K and sodium-ammonia with 18, 14, and 10 MPM at T=222K). These data were analyzed to determine the acoustic collective excitation dispersion relation and the linewidth. Deviations from the Bohm-Staver model for electron-ion coupling are discussed for the low electronic densities. For the …

Resonant And Non-Resonant Inelastic X-Ray Scattering Of Copper Phthalocyanine, Michelle Deleene Tuel-Benckendorf

Masters Theses

With the ever-changing demands of technology and the desire to use new materials to replace the old, researchers have the job to not only find alternative materials, but also understand their properties. There continues to be extensive research in the properties of organic semiconductors, for use in many microelectronic applications. There is very little known about the excitation properties of these materials. For my research, I have chosen to study the electronic excitations of copper phthalocyanine (CuPc), one specific organic semiconductor. To do this, we used resonant and non-resonant inelastic x-ray scattering to measure the evolution of excitations as a …

Plasma Blobs Observed By Ground-Based Optical And Radio Techniques In The Brazilian Tropical Sector, A. A. Pimenta, Y. Sahai, J. A. Bittencourt, M. A. Abdu, H. Takahashi, Michael J. Taylor

All Physics Faculty Publications

Ground-based optical and radio observations were carried out in the tropical region in Brazil, during the period from October 1998 to September 2000, and on several occasions we detected F-region plasma blob (localized discrete plasma density enhancement) events. These are the first observations of blobs in the tropical F-region using combined ground-based optical and radio techniques. Allsky images were used to map the spatial extension and temporal location of plasma blobs and ionosonde and photometer measurements were used to measure the plasma densities. Interesting cases of plasma blob events were observed on October 07, 1999 and March 04, 2000 over …

A Dunking Bird Of The Second Kind, Nadine Abraham, Peter Palffy-Muhoray

Peter Palffy-Muhoray

The conventional dunking bird is a heat engine that relies on the temperature difference between the head and the tail of the bird for its operation. We describe a new type of dunking bird that is not a heat engine, but one that directly uses the chemical potential difference between liquid water and its vapor.

Simulations Of Dynamically Triangulated Gravity -- An Algorithm For Arbitrary Dimension, Simon Catterall

Physics - All Scholarship

Recent models for discrete euclidean quantum gravity incorporate a sum over simplicial triangulations. We describe an algorithm for simulating such models in general dimensions. As illustration we show results from simulations in four dimensions

Characterization Of Ultrathin Gate Dielectrics And Multilayer Charge Injection Barriers, Edwin M. Dons

Dissertations

Since the invention of the first integrated circuit, the semiconductor industry has distinguished itself by a phenomenally rapid pace of improvements in device performance. This trend of ever smaller and faster devices is a result of the ability to exponentially reduce feature sizes of integrated circuits, a trend commonly known as "scaling". A reduction of overall feature sizes requires a simultaneous reduction in the thickness of the gate dielectric, SiO₂, of a MOSFET. Gate oxides in the ultrathin regime (<35 A) feature a large direct tunneling leakage current. The presence of this leakage current requires a reevaluation of standard characterization techniques as well as a reevaluation of the continued usefulness of SiO₂ as the gate dielectric of choice for future applications. On the other hand, a thorough understanding of …

Understanding The Origin Of The Recovery Of Superconductivity In Halogenated Ybco Single Crystal : Atomic Structure Study, Lamine Mohamed Kollakoye Dieng

Dissertations

The recovery of superconductivity in underdoped YBa₂Cu₃O_6+y (YBCO) by exposure to bromine, iodine, chlorine and fluorine is a long-standing problem which has not been clearly resolved. The key question concerns the role of these halogens in the lattice. In order to shed light to this problem, we have performed multiple-edge x-ray absorption fine structure (XAFS) measurements about the Y K, Ba L₃, I L₃, Cu K and Br K-edges at room temperature on brominated (non-brominated) and iodinated (non-iodinated) YBCO single crystals. Our XAFS results at the Br K (brominated) and I …

Dynamics Of M-Theory Vacua, John Donoghue

John Donoghue

At very early times, the universe was not in a vacuum state. Under the assumtion that the deviation from equillibrium was large, in particular that it is higher than the scale of inflation, we analyse the conditions for local transitions between states that are related to different vacua. All pathways lead to an attractor solution of a description of the universe by eternal inflation with domains that have different low energy parameters. The generic case favors transitions between states that have significantly different parameters rather than jumps between nearby states in parameter space. I argue that the strong CP problem …

Realization Of The Einstein-Podolsky-Rosen Paradox Using Momentum- And Position-Entangled Photons From Spontaneous Parametric Down Conversion, John C. Howell, Ryan S. Bennink, Sean J. Bentley, Robert W. Boyd

Mathematics, Physics, and Computer Science Faculty Articles and Research

We report on a momentum-position realization of the EPR paradox using direct detection in the near and far fields of the photons emitted by collinear type-II phase-matched parametric down conversion. Using this approach we achieved a measured two-photon momentum-position variance product of 0.01ℏ², which dramatically violates the bounds for the EPR and separability criteria.

Gold Adatoms And Dimers On Relaxed Graphite Surfaces, Guan Ming Wang, Joseph J. Belbruno, Steven D. Kenny, Roger Smith

Dartmouth Scholarship

The interaction of deposited gold adatoms and dimers with multilayer relaxed graphite surfaces is investigated through a density functional approach with numerical orbitals and a relativistic core pseudopotential. The energy landscape for a gold adatom along [110] agrees with scanning tunneling microscopy observations including the preferred β binding site for adatoms and the mobility difference between silver and gold adatoms. Deposited particles are shown to induce surface deformation and polarization. Static relaxation and dynamic simulations indicate that the energetically preferred binding orientation for a gold dimer is normal rather than parallel to the graphite surface. The dimer response to a …

Consequences Of Gravitational Radiation Recoil, David Merritt, Miloš Milosavljević, Marc Favata, Scott A. Hughes, Daniel E. Holz

Department of Physics and Astronomy Faculty Scholarship and Creative Works

Coalescing binary black holes experience an impulsive kick from anisotropic emission of gravitational waves. Recoil velocities are sufficient to eject most coalescing black holes from dwarf galaxies and globular clusters, which may explain the apparent absence of massive black holes in these systems. Ejection from giant elliptical galaxies would be rare, but coalescing black holes are displaced from the center and fall back on a timescale of order the half-mass crossing time. Displacement of the black holes transfers energy to the stars in the nucleus and can convert a steep density cusp into a core. Radiation recoil calls into question …

How Black Holes Get Their Kicks: Gravitational Radiation Recoil Revisited, Marc Favata, Scott A. Hughes, Daniel E. Holz

Department of Physics and Astronomy Faculty Scholarship and Creative Works

Gravitational waves from the coalescence of binary black holes carry away linear momentum, causing center of mass recoil. This "radiation rocket" effect has important implications for systems with escape speeds of order the recoil velocity. We revisit this problem using black hole perturbation theory, treating the binary as a test mass spiraling into a spinning hole. For extreme ratios (q ≡ m1/m2 ≪ 1), we compute the recoil for the slow in-spiral epoch of binary coalescence very accurately; these results can be extrapolated to q ∼ 0.4 with modest accuracy. Although the recoil from the final plunge contributes significantly to …