Physical Sciences and Mathematics Commons^™

The Role Of Bandgap In The Secondary Electron Emission Of Small Bandgap Semiconductors: Studies Of Graphitic Carbon, Neal E. Nickles

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The question of whether the small bandgaps of semiconductors play a significant role in their secondary electron emission properties is investigated by studying evaporated graphitic amorphous carbon, which has a roughly 0.5 eV bandgap, in comparison with microcrystalline graphite, which has zero bandgap. The graphitic amorphous carbon is found to have a 30% increase in its maximum secondary electron yield over that of two microcrystalline graphite samples with comparable secondary electron yields: highly oriented pyrolytic graphite and colloidal graphite. The potentially confounding influence of the vacuum level has been isolated through the measurement of the photoelectron onset energy of the …

The Relationship Between Magnetic Interactions And Near Neighbor Interatomic Distances In The Transition Metal Sublattice Of R(Mn/Fe)₆A₆(R=Nd Or Sm, A=Ge Or Sn), G. K. Marasinghe, J. Han, William Joseph James, William B. Yelon, Naushad Ali

Chemistry Faculty Research & Creative Works

The magnetic and crystallographic structures of R(Fe/Mn)₆A₆ (R=Nd or Sm and A = Ge or Sn) intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides (A = Sn) and germanides (A = Ge), the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (x ≤2 ) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties …

Single-Molecule Detection, Wesley Carlton Parker

Masters Theses

Single-molecule detection (SMD) provides a practical method of examining the behavior of individual molecules. This has application both for fundamental studies of particle dynamics such as diffusion in solutions, and for bio-technology applications such as DNA sequencing.

In this thesis I discuss two confocal epi-illumination microscopes constructed at UTSI and used for single-molecule detection and fluorescence correlation spectroscopy. Examples of data collected from experiments using each instrument is presented in which solutions of the fluorescent dye sulforhodamine 101 are analyzed. An example of the use of the instrument to detect fluorescence quenching is also presented.

Orbital Ordering In Paramagnetic Lamno₃ And Kcuf₃, Julia E. Medvedeva, Michael A. Korotin, Vladimir I. Anisimov, Arthur J. Freeman

Physics Faculty Research & Creative Works

Ab initio studies of the stability of orbital ordering, its coupling to magnetic structure and its possible origins (electron-phonon and/or electron-electron interactions) are reported for two perovskite systems, LaMnO₃ and KCuF₃. We present an average spin state calculational scheme that allowed us to treat a paramagnetic state and to succesfully describe the experimental magnetic or orbital phase diagram of both LaMnO₃ and KCuF₃ in crystal structures when the Jahn-Teller distortions are neglected. Hence, we conclude that the orbital ordering in both compounds is purely electronic in origin.

Calculation Of Damping Rates In Thin Inhomogeneous Ferromagnetic Films Due To Coupling To Lattice Vibrations, R. D. Mcmichael, Andrew Kunz

Physics Faculty Research and Publications

This article describes calculations of ferromagnetic resonance damping rates due to coupling between the magnetization and lattice vibrations through inhomogeneities. The mechanisms we have explored include generation of shear phonons through inhomogeneous anisotropy and generation of both longitudinal and shear phonons through inhomogeneous magnetostriction. In both cases, inhomogeneities couple the uniform precession to finite wave vector phonons. For both coupling mechanisms, the predicted damping rate is on the order of 10⁶ s^-21 in transition metals. The damping rate by these mechanisms is inversely proportional to the fifth power of the shear phonon velocity, and may play a significant …

Review Of Tuxedo Park, Michael F. Russo

Faculty Publications

No abstract provided.

The Meyer-Neldel Rule For A Property Determined By Two Transport Mechanisms, Ralf Widenhorn, Armin Rest, Erik Bodegom

Physics Faculty Publications and Presentations

We propose that the Meyer-Neldel rule (MNR) arises naturally for a quantity where both an intrinsic process as well as a process involving impurities contribute. The strength of the latter depends solely on the density of the impurities. This leads to a spread in the apparent activation energy of the measured quantity and the observation of the MNR, even though the intrinsic processes have fixed activation energies. A consequence of the MNR is the occurrence of a temperature T[sub MN] where a measured parameter is independent of the activation energy. For the system studied, the MNR does not accurately predict …

Residual Images In Charged-Coupled Device Detectors, Armin Rest, Lars Mündermann, Ralf Widenhorn, Erik Bodegom, T. C. Mcglinn

Physics Faculty Publications and Presentations

We present results of a systematic study of persistent, or residual, images that occur in charged-coupled device (CCD) detectors. A phenomenological model for these residual images, also known as "ghosting," is introduced. This model relates the excess dark current in a CCD after exposure to the number of filled impurity sites which is tested for various temperatures and exposure times. We experimentally derive values for the cross section, density, and characteristic energy of the impurity sites responsible for the residual images.

Residential Radon Exposure And Lung Cancer: Variation In Risk Estimates Using Alternative Exposure Scenarios, R. William Field, Brian J. Smith, Daniel J. Steck, Charles F. Lynch

Physics Faculty Publications

The most direct way to derive risk estimates for residential radon progeny exposure is through epidemiologic studies that examine the association between residential radon exposure and lung cancer. However, the National Research Council concluded that the inconsistency among prior residential radon case-control studies was largely a consequence of errors in radon dosimetry. This paper examines the impact of applying various epidemiologic dosimetry models for radon exposure assessment using a common data set from the Iowa Radon Lung Cancer Study (IRLCS). The IRLCS uniquely combined enhanced dosimetric techniques, individual mobility assessment, and expert histologic review to examine the relationship between cumulative …

Search For Lepton-Flavor Violation In E+P Collisions At Desy Hera, S. Chekanov, M. Derrick, 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, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

A search has been made for lepton-flavor-violating interactions of the type e+p→lX, where l denotes a μ or τ with high transverse momentum, at a center-of-mass energy √s of 300 GeV with an integrated luminosity of 47.7 pb-1 using the ZEUS detector at HERA. No evidence was found for lepton-flavor violation and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below √s, limits are set on λeq1βlq, where λeq1 is the coupling of the LQ to an electron and a first-generation quark q1 and βlq is the branching ration of the LQ to l …

Direct And Sensitive Measurement Of Two-Photon Absorption Cross Sections, Peifang Tian, D. Keusters, Warren Warren

Peifang Tian

Summary form only given. We present a direct method to detect weak two-photon absorption (TPA) signals. As a proof of principle, we have measured the TPA cross section δ for rhodamine 6G (R6G) in methanol and obtained a value which agrees with other results. The technique may be very useful in biomedical imaging.

Comparision Of Measured Convection Velocities With Calcuulations Based On Electric Potential Model, Daniel E. Britton

Honors Capstone Projects and Theses

No abstract provided.

Search For The Scalar Top Quark In Pp̅ Collisions At √S = 1.8 Tev, V. M. Abazov, Gregory R. Snow, Do Collaboration

Gregory Snow Publications

We have performed a search for scalar top quark (stop) pair production in the inclusive electronmuon- missing transverse energy final state, using a sample of pp̅ events corresponding to 108.3 pb^-1 of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, t̅→ b χ₁⁺ and t̅→bℓν, no evidence for signal is found. We derive cross-section limits as a function of stop (t̅), …

Projectile And Target Ionization In Mev U⁻¹ Collisions Of Xe Ions With N2, Ronald E. Olson, R. L. Watson, V. Horvat, K. E. Zaharakis

Physics Faculty Research & Creative Works

Experimental cross sections are presented for single and multiple electron stripping from Xe¹⁸⁺ projectiles in collisions with N₂ at energies 2.0-9.3 MeV u^-1. The data are compared to 2-30 MeV u^-1 n-body classical trajectory Monte Carlo calculations that explicitly include electrons on both centres. Two-centre electron-electron (e-e) and electron-screened nuclear interactions contribute to the ionization reactions. The computations are in reasonable accord for the total stripping cross section but underestimate the higher stages of multiple electron loss. An energy deposition model gives improved agreement with experiment. The energy dependence of the total stripping cross section …

Coherent Vs Incoherent Interlayer Transport In Layered Metals, Gary L. Gard, J. Wosnitza, J. Hagel, J. S. Qualls, J. S. Brooks, E. Balthes, D. Schweitzer, J. A. Schlueter, U. Geiser, Javid Mohtasham, Rolf Walter Winter

Chemistry Faculty Publications and Presentations

The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Q590°(field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.

Γ Production And Polarization In Pp̅ Collisions At √S= 1.8 Tev, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on measurements of the ϒ(1S), ϒ(2S), and ϒ(3S) differential cross sections (d²σ/dp_Tdy)|y|pp̅ collisions at √s = 1.8 TeV using a sample of 77±3 pb^-1 collected by the collider detector at Fermilab. The three resonances were reconstructed through the decay ϒ→μ⁺μ^-. The measured angular distribution of the muons in the ϒ(1S) rest frame is consistent with unpolarized meson production.

Charged Jet Evolution And The Underlying Event In Proton-Antiproton Collisions At 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

The growth and development of ‘‘charged particle jets’’ produced in proton-antiproton collisions at 1.8 TeV are studied over a transverse momentum range from 0.5 GeV/c to 50 GeV/c. A variety of leading (highest transverse momentum) charged jet observables are compared with the QCD Monte Carlo models HERWIG, ISAJET, and PYTHIA. The models describe fairly well the multiplicity distribution of charged particles within the leading charged jet, the size of the leading charged jet, the radial distribution of charged particles and transverse momentum around the leading charged jet direction, and the momentum distribution of charged particles within the …

Measurement Of The Photon-Proton Total Cross Section At A Center-Of-Mass Energy Of 209 Gev At Hera, S. Chekanov, M. Derrick, 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, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli

Faculty Publications

The photon-proton total cross section has been measured in the process e+ p → e+ γp → e+ X with the ZEUS detector at HERA. Events were collected with photon virtuality Q2 < 0.02 GeV2 and average γp center-of-mass energy Wγp = 209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb-1. The measured total cross section is σtotγp = 174 ± 1 (stat.) ± 13 (syst.) μb. The energy dependence of the cross section is compatible with parameterizations of high-energy pp and pap data. © 2002 Elsevier Science B.V. All rights reserved.

The Fission Properties Of Curium Separated From Spent Nuclear Fuel, William Culbreth, Elizabeth Bakker, Jason Viggato

Separations Campaign (TRP)

Curium poses special problems in the chemical preparation of spent nuclear fuel for transmutation. Once separated from the other minor actinides, the seven curium isotopes in spent fuel can lead to nuclear fission with the subsequent release of a large amount of radiation. Several isotopes of curium also generate a significant amount of heat by radioactive decay. Sustained fission can be avoided by preventing the accumulation by more that a critical mass of curium. The heat generation of curium presents even more restriction on the mass of curium that can safely be contained in one location.

To analyze the nuclear …

Multielectron System In An Ultrashort, Intense Laser Field: A Nonperturbative, Time-Dependent Two-Active-Electron Approach, G. Lagmago Kamta, Anthony F. Starace

Department of Physics and Astronomy: Faculty Publications

We present a two-active-electron (TAE) approach for solving the time-dependent Schrödinger equation (TDSE) for the interaction of a multi-electron system with an ultrashort, intense, and linearly polarized laser pulse [Lagmago Kamta and Starace, Phys. Rev. Lett. 86, 5687 (2001)]. A technique for obtaining angular distributions for double ionization by such pulses is also described. The approach for solving the TDSE in the TAE approximation is full dimensional and accounts for correlations between the two electrons, as well as the polarization of the core. It is based on a configuration-interaction expansion of the time-dependent wave function in terms of one-electron …

Direct Search For Charged Higgs Bosons In Decays Of Top Quarks, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present a search for charged Higgs bosons in decays of pair-produced top quarks in pp̅ collisions at√s = 1.8 TeV recorded by the D0 detector at the Fermilab Tevatron collider. With no evidence for signal, we exclude most regions of the (M_H±, tan β) parameter space where the decay t → H⁺b has a branching fraction >0.36 and B(H^± → τν_τ is large.

Diffractive Dijet Production At √S= 630 And 1800 Gev At The Fermilab Tevatron, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report a measurement of the diffractive structure function F_jj^D of the antiproton obtained from a study of dijet events produced in association with a leading antiproton in p̅p collisions at √s =630 GeV at the Fermilab Tevatron. The ratio of F_jj^D at √s =630 GeV to F_jj^D obtained from a similar measurement at √s =1800 GeV is compared with expectations from QCD factorization and other theoretical predictions. We also report a measurement of the ξ(x-Pomeron) and β(x of parton in Pomeron) dependence of F_jj^D at √s =1800 GeV. In the region …

Coercive Fields In Ferroelectrics: A Case Study In Lithium Niobate And Lithium Tantalate`, Sungwon Kim, Venkatraman Gopalan, Alexei Gruverman

Alexei Gruverman Publications

The experimentally measured coercive electric fields for domain reversal in ferroelectrics are typically many orders of magnitude lower than the estimates from phenomenological free-energy theory. This letter specifically investigates the influence of polarization gradients at pre-existing 180° domain walls in ferroelectrics on coercive fields for domain wall motion. It is shown that the ratio of theoretical coercive field without and with a preexisting domain wall is directly proportional to the ratio x_o /a, where a is the lattice parameter and 2x_o is the polarization wall width. This factor is 7.5–45 for a 20–120 nm wall width, the latter …

Radiation Transport Modeling Of Beam-Target Experiments For The Aaa Project: Quaterly Report, 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 500 or more neutrons that can activate fission products or induce the fission of transuranic isotopes.

The Monte Carlo radiation transport code MCNPX developed at LANL is an important tool in the design of transmuter technology. It must be validated, however, for the neutron energy that will be employed. Experiments are being …

Nuclear Criticality Analyses Of Separations Processes For The Transmutation Fuel Cycle: Quarterly Report, William Culbreth, Pang Tao

Separations Campaign (TRP)

During the first two quarters of the work, the tasks included training students in the use of Monte Carlo codes used in radiation transport studies and the assessment of neutron multiplication factors for specific problems outlined by ANL-East through Drs. Laidler and Vandegrift.

The proposal also included objectives for the first year of work on this project, as listed below. The work conducted in the second quarter of the project was in partial completion of these objectives.

• Train UNLV students in the use of SCALE and/or MCNP for the assessment of nuclear criticality.

• Assess neutron multiplication factor, k …

De Haas-Van Alphen Oscillations In The Quasi-Two-Dimensional Organic Conductor Κ-(Et)2cu(Ncs)2: The Magnetic Breakdown Approach, V. M. Gvozdikov, Yuriy V. Pershin Dr, E. Steep, A. G. M. Jansen, P. Wyder

Faculty Publications

We present both experimental data and an analytic theory for the de Haas–van Alphen ~dHvA! effect in the two-dimensional organic single-crystal conductor k -(ET)2Cu(NCS)2. We show that the magnetization oscillation pattern and the fast Fourier transform (FFT) spectrum of our measurements are well described theoretically within the coherent magnetic breakdown (MB) model for a two-dimensional Fermi surface consisting of two open sheets and closed pockets connected by magnetic breakdown centers. The spectrum of Landau quantized energy levels changes substantially due to the MB. Landau bands develop whose bandwidth and relative distance between them oscillate in inverse magnetic field. These oscillations …

Transport Properties Of Polycrystalline Type-I Sn Clathrates, G. S. Nolas, J. L. Cohn, Jeffrey Dyck, C. Uher, J. Lang

Jeffrey Dyck

Thermal conductivity, resistivity, Seebeck coefficient, and Hall measurements on polycrystalline Sn-clathrate compounds with the type-I hydrate crystal structure are reported. Interstitial alkali-metal atoms in these compounds reside inside polyhedral cavities formed by the tetrahedrally bonded Sn network atoms. Localized disorder associated with “rattling” motion of these interstitial atoms contributes to the low thermal conductivity of these semiconducting compounds. The Hall coefficient and resistivity for some compounds exhibit nonmonotonic temperature dependences consistent with a crossover with decreasing temperature from conduction-band to impurity-band conduction. The carrier mobility is found to be low even in the absence of interstitial atoms within the Sn …

Three-Body Dynamics In Hydrogen Ionization By Fast Highly Charged Particles, J. Fiol, Ronald E. Olson

Physics Faculty Research & Creative Works

Electron double and triple differential cross sections are calculated as a function of projectile momentum transfer for ionization of ground and excited state hydrogen by 3.6 MeV u^-1 C⁶⁺ and Au⁵³⁺ ions. These three-body Coulomb systems are investigated using the classical-trajectory Monte Carlo and continuum distorted wave methods that incorporate all interactions including the nuclear-nuclear potential. The calculations allow one to distinguish cross section features associated with three collision mechanisms. The first is due to distance collisions that lead primarily to a binary interaction between the projectile and electron. The second is a strong three-body interaction by …

Design And Analysis Of A Process For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides, Yitung Chen, Darrell Pepper, Randy Clarksean

Fuels Campaign (TRP)

UNLV has developed and will continue to develop process models for the analysis of melt casting processes. This work will continue to be performed under the guidance of Argonne National Laboratory (ANL) engineers to ensure that their knowledge and experience benefits the project. The research to be conducted during the second year will center on performing detailed analyses on a conceptual design of an inductively heated skull-crucible casting furnace. Processing conditions will be analyzed, basic models utilized, and detailed heat and mass transfer models will be developed to analyze the most promising processes. The goal of this second year is …

Absolute Tin(111) Step Energies From Analysis Of Anisotropic Island Shape Fluctuations, S. Kodambaka, V. Petrova, S. V. Khare, Duane D. Johnson, I. Petrov, J. E. Greene

Duane D. Johnson

In situ high-temperature (1165–1248 K) scanning tunneling microscopy was used to measure fluctuations around the equilibrium shape of two-dimensional vacancy islands on TiN(111) terraces. From the equilibrium shape, the ratio of the two ⟨110⟩ step energies was found to be 0.72±0.02. Combining this with the results of an exact approach for analysis of shape fluctuations, applicable to highly anisotropic islands, we obtain absolute values for step energies and step stiffnesses as a function of orientation.