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Articles 1 - 20 of 20
Full-Text Articles in Condensed Matter Physics
Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard
Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard
Faculty Publications – Chemistry
Electrons near roughened Ag and Au surfaces with chemisorbed dielectric overlayers of alkanethiol or alkaneselenol self-assembled monolayers are shown to move within the sulfur or selenium head-group layer on the metal terraces. The electrons exist in image states with respect to Ag or Au step edges. There is no substantial image force between the electrons and the terraces.
Thermoelectric Single-Photon Detectors For X-Ray/Uv Radiation, G. G. Fritz, K. S. Wood, D. Van Vechten, A. L. Gyulamiryan, A. S. Kuzanyan, N. J. Giordano, T. M. Jacobs, H.-D. Wu, J. S. Horwitz, Armen Gulian
Thermoelectric Single-Photon Detectors For X-Ray/Uv Radiation, G. G. Fritz, K. S. Wood, D. Van Vechten, A. L. Gyulamiryan, A. S. Kuzanyan, N. J. Giordano, T. M. Jacobs, H.-D. Wu, J. S. Horwitz, Armen Gulian
Mathematics, Physics, and Computer Science Faculty Articles and Research
A feasibility study of megapixel microcalorimeter arrays, based on thermoelectric energy to voltage conversion and digital superconducting readout, is presented. The design concept originated from the philosophy of employing the simplest principles at the single-pixel level to enable large arrays without sacrificing energy resolution, fast operation speed, and quantum efficiency. Initial experimental tests confirm the basic predictions of theory, and show no major obstacle in achieving the desired characteristics.
Low-Frequency Crossover Of The Fractional Power-Law Conductivity In Srruo3, J. S. Dodge, Christopher P. Weber, J. Corson, J. Orenstein, Z. Schlesinger, J. W. Reiner, M. R. Beasley
Low-Frequency Crossover Of The Fractional Power-Law Conductivity In Srruo3, J. S. Dodge, Christopher P. Weber, J. Corson, J. Orenstein, Z. Schlesinger, J. W. Reiner, M. R. Beasley
Physics
We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO 3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, with an analytic structure fundamentally different from that predicted by the standard theory of metals.
Temperature-Induced Configurational Excitations For Predicting Thermodynamic And Mechanical Properties Of Alloys, Duane D. Johnson, Andrei V. Smirnov, J. B. Staunton, F. J. Pinski, W. A. Shelton
Temperature-Induced Configurational Excitations For Predicting Thermodynamic And Mechanical Properties Of Alloys, Duane D. Johnson, Andrei V. Smirnov, J. B. Staunton, F. J. Pinski, W. A. Shelton
Duane D. Johnson
We show that a structural energy difference, ΔE, must include explicit symmetry-breaking changes of the electronic structure due to temperature-induced configurational excitations, and why ΔE at T=0 K is not necessarily relevant to thermodynamic and mechanical modeling. In Ni3V, we calculate a tenfold decrease of ΔE between D022 and L12 structures from T=0 K to states of order relevant to experiment. ΔE calculated directly from states with short-range order (8 meV) or with low partial order (7–12 meV) agree with high-T experiment (10 meV).
Powre: Driven Nonequilibrium Systems With Quenched Disorder: A Renormalization-Group Study, Susan R. Mckay
Powre: Driven Nonequilibrium Systems With Quenched Disorder: A Renormalization-Group Study, Susan R. Mckay
University of Maine Office of Research Administration: Grant Reports
This theory project develops a position-space renormalization-group approach to study driven diffusive lattice gases; the theory will be modified and applied to interacting cases and systems with quenched randomness. Systems driven far from equilibrium are prevalent in nature and particularly challenging with respect to fundamental understanding and property prediction. The models to be studied in this project are simple prototypes related to a variety of complex systems such as biological populations, binary fluid flow through random media, and fast ionic conductors. This is a research enhancement grant made under the Professional Opportunities for Women in Research and Education (POWRE) program. …
Effect Of Disorder On Perpendicular Magnetotransport In Co/Cu Multilayers, Evgeny Y. Tsymbal
Effect Of Disorder On Perpendicular Magnetotransport In Co/Cu Multilayers, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
We investigate the spin-dependent conductance of the Co/Cu multilayers in the current-perpendicular-tothe- plane (CPP) geometry. Using a realistic tight-binding model for the electronic band structure of the multilayer, and introducing disorder in the on-site atomic energies we calculate the conductance and giant magnetoresistance (GMR) within the quantum-mechanical linear response theory by performing averaging over random disorder configurations. By varying the thickness and the number of individual layers and the degree of disorder in the multilayers, we analyze factors influencing the CPP GMR. In particular, we show the importance of the thickness-dependent interface resistance, which depends on the mean free path …
Theory Of Magnetostatic Coupling In Thin-Film Rectangular Magnetic Elements, Evgeny Y. Tsymbal
Theory Of Magnetostatic Coupling In Thin-Film Rectangular Magnetic Elements, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
A theory of magnetostatic coupling in thin-film uniformly magnetized arrays of rectangular magnetic elements is presented. Analytic expressions for the magnetostatic energy and the dipolar fields are derived. The influence of the aspect ratio and the spacing between the elements on the magnetostatic coupling is investigated. It is found that increasing the aspect ratio reduces the critical distance between the elements, above which the magnetostatic inter-element coupling can be neglected.
Spin Fluctuations In Nearly Magnetic Metals From Ab Initio Dynamical Spin Susceptibility Calculations: Application To Pd And Cr95v5, J. B. Staunton, J. Poulter, B. Ginatempo, E. Bruno, Duane D. Johnson
Spin Fluctuations In Nearly Magnetic Metals From Ab Initio Dynamical Spin Susceptibility Calculations: Application To Pd And Cr95v5, J. B. Staunton, J. Poulter, B. Ginatempo, E. Bruno, Duane D. Johnson
Duane D. Johnson
We describe our theoretical formalism and computational scheme for making ab initio calculations of the dynamic paramagnetic spin susceptibilities of metals and alloys at finite temperatures. Its basis is time-dependent density functional theory within an electronic multiple scattering, imaginary time Green function formalism. Results receive a natural interpretation in terms of overdamped oscillator systems making them suitable for incorporation into spin fluctuation theories. For illustration we apply our method to the nearly ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5. We compare and contrast the spin dynamics of these two metals and in each case identify those fluctuations …
Oxygen-Induced Positive Spin Polarization From Fe In The Vacuum Barrier, Evgeny Y. Tsymbal, Ivan I. Oleinik, David G. Pettifor
Oxygen-Induced Positive Spin Polarization From Fe In The Vacuum Barrier, Evgeny Y. Tsymbal, Ivan I. Oleinik, David G. Pettifor
Evgeny Tsymbal Publications
Bonding at the ferromagnet–insulator interface is an important factor which influences spin polarization of the tunneling current in ferromagnetic tunnel junctions. In this article we investigate the spin-polarized electronic structure of the (001) surface of body-centered-cubic iron covered by an oxygen overlayer, as this could reflect the mechanism of bonding and spin polarization in iron/oxide tunnel junctions. The Fe/O atomic structure is optimized using the plane-wave code CASTEP within the spin-polarized generalized-gradient approximation. The electronic structure and local densities of states are calculated using the linear muffin-tin orbital method. The results show hybridization of the iron 3d orbitals with …
Structural And Electronic Properties Of Cobalt/Alumina Tunnel Junctions From First Principles, Ivan I. Oleinik, Evgeny Y. Tsymbal, David G. Pettifor
Structural And Electronic Properties Of Cobalt/Alumina Tunnel Junctions From First Principles, Ivan I. Oleinik, Evgeny Y. Tsymbal, David G. Pettifor
Evgeny Tsymbal Publications
A detailed first-principles study of the atomic and electronic structure of the Co/Al2O3/Co magnetic tunnel junction has been performed in order to elucidate the key features determining the spin-dependent tunneling. The atomic structure of the multilayer with the O- and Al-terminated interfaces between fcc Co(111) and crystalline α-Al2O3(0001) has been optimized using self-consistent spin-polarized calculations within densityfunctional theory and the generalized gradient approximation. We found that the relaxed atomic structure of the O-terminated interface is characterized by a rippling of the Co interfacial plane, the average Co-O bond length being 2.04 Å …
Electronic Scattering From Co/Cu Interfaces: In-Situ Measurement And Comparison With Theory, W. E. Bailey, Shan X. Wang, Evgeny Y. Tsymbal
Electronic Scattering From Co/Cu Interfaces: In-Situ Measurement And Comparison With Theory, W. E. Bailey, Shan X. Wang, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
The full thickness-dependent electrical conductivity of polycrystalline NiO/Co/Cu/Co spin-valve structures was measured in situ during ion-beam deposition and compared with calculations based on realistic band structure. We have found striking features in the experimental conductivity which are unexpected from widely used semiclassical free-electron models. Addition of ∼ 1 ML Co to a NiO/Co/Cu surface causes the net film conductance to decrease; the reverse case of Cu on NiO/Co shows a strong positive curvature of the thicknessdependent conductance, indicating a reduction of the conductivity in Cu near the interface with Co. Quantitative agreement is found between the experimental thickness-dependent film conductance …
Behavior Of Grain Boundary Resistivity In Metals Predicted By A Two-Dimensional Model, Rand Dannenberg, Alexander H. King
Behavior Of Grain Boundary Resistivity In Metals Predicted By A Two-Dimensional Model, Rand Dannenberg, Alexander H. King
Alexander H. King
The behavior of a model for the specific grain boundary resistivity in metallic bamboo conductor lines is developed and compared to other theoretical treatments, and to experiment. The grain boundary is modeled as an array of scatterers on a plane. The scatterers are called “vacancy-ion” complexes, in which the vacancy represents the boundary free volume, and the ion is an atom adjacent to the vacancy. Three cases are investigated, that of noninterfering scatterers, a continuum of interfering scatterers, and discrete interfering scatterers. The approximations used lead to a specific grain boundary resistivity ∼10−16 Ω m2 for aluminum, in agreement with …
Measurements Of Electronic Properties Of Conducting Spacecraft Materials With Application To The Modeling Of Spacecraft Charging, W. Y. Chang, Jr Dennison, Parker Judd
Measurements Of Electronic Properties Of Conducting Spacecraft Materials With Application To The Modeling Of Spacecraft Charging, W. Y. Chang, Jr Dennison, Parker Judd
Conference Proceedings
Many spacecraft system anomalies and component failures are known to result from spacecraft charging which is due to the bombardments of spacecraft by energetic electrons, ions, and photons in natural space surrounding [Hastings and Garrett, 1996; Bedingfield et al., 1996; Leach et al., 1995]. To assist spacecraft designers in accommodating and mitigating the harmful charging effects on spacecraft, NASA has developed an extensive set of engineering tools to predict the extent of charging in various spacecraft environments (for example, NASCAP/LEO, NASCAP/GEO, and POLAR) [Mandell et al., 1993]. However, current NASCAP databases lack electronic properties …
Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B V. Vayner, D C. Ferguson, C D. Thomson, Jr Dennison, R E. Davies
Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B V. Vayner, D C. Ferguson, C D. Thomson, Jr Dennison, R E. Davies
Conference Proceedings
Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment1–4. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed2,5. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. …
Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B V. Vayner, W A. Degroot, D C. Ferguson, C D. Thomson, Jr Dennison, R E. Davies
Inception Of Snapover And Gas Induced Glow Discharges, J. T. Galofaro, B V. Vayner, W A. Degroot, D C. Ferguson, C D. Thomson, Jr Dennison, R E. Davies
Conference Proceedings
Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment1-4. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed2,5. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. …
Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, Jr Dennison
Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, Jr Dennison
Journal Articles
Secondary electron emission (SEE) plays a key role in spacecraft charging [Garrett, 1981; Frooninckx and Sojka, 1992] . As a result, spacecraft charging codes require knowledge of the SEE characteristics of various materials in order to predict vehicle potentials in various orbital environments [Katz, et. al., 1986]. Because SEE is a surface phenomenon, occurring in the first few atomic layers of a material, the SEE characteristics of a given surface are extremely sensitive to changes in surface condition—e.g., the addition or removal of surface contaminants, or changes in surface morphology. That spacecraft surfaces …
Quantum-Well Resistivity For Perpendicular Transport In Magnetic Layered Systems, Evgeny Y. Tsymbal, David G. Pettifor
Quantum-Well Resistivity For Perpendicular Transport In Magnetic Layered Systems, Evgeny Y. Tsymbal, David G. Pettifor
Evgeny Tsymbal Publications
We show that quantum-well states enhance the current-perpendicular-to-planes resistivity of a metal film compared to the resistivity in the bulk at film thicknesses comparable with the mean free path due to the reduced number of conducting channels within the potential-well structure. This makes the mean free path an important parameter, which must be taken into account for the accurate treatment of results on currentperpendicular- to-plane giant magnetoresistance, rather than ignored by applying the two-current series-resistor model.
Structural Instabilities In Strontium Titanate From First-Principles Calculations, Christopher A. Lasota
Structural Instabilities In Strontium Titanate From First-Principles Calculations, Christopher A. Lasota
Dissertations, Theses, and Masters Projects
For some time now, first-principles calculation methods have proven to be an effective tool for investigating the physics of condensed matter systems. The additional use of density functional theory (DFT) and the local density approximation (LDA) has permitted even complex materials to be studied on desktop workstations with remarkable success. The incorporation of linear response theory into these methods has extended their power, allowing investigation of important dynamical properties.;Contained within the following pages are the results of a first-principles study of SrTiO3. This transition metal oxide is often grouped with ferroelectric materials, due to its similar composition and perovskite structure. …
Plasma Source Ion Implantation Of High Voltage Electrodes, Thomas Joseph Venhaus
Plasma Source Ion Implantation Of High Voltage Electrodes, Thomas Joseph Venhaus
Dissertations, Theses, and Masters Projects
Field emission and breakdown characteristics of high voltage, large area electrodes determine the performance of many vacuum-based electron sources. A corroborative project with the Thomas Jefferson National Accelerator Facility involves studying the behavior of such electrodes after nitrogen ion implantation. A Plasma Source Ion Implantation (PSII) facility is designed and constructed at William and Mary, and used to treat stainless steel electrodes. PSII is a novel implantation technique developed at the University of Wisconsin-Madison. A workpiece is submerged in a quiescent plasma of the species to be implanted. A series of high, negative voltages (30--100 kV) is applied to the …
Surface Processing By Rfi Pecvd And Rfi Psii, Lingling Wu
Surface Processing By Rfi Pecvd And Rfi Psii, Lingling Wu
Dissertations, Theses, and Masters Projects
An RFI plasma enhanced chemical vapor deposition (PECVD) system and a large-scale RF plasma source immersion ion implantation (PSII) system were designed and built to study two forms of 3-D surface processing, PECVD and PSII. Using the RFI PECVD system, Ti-6Al-4V substrates were coated with diamond-like carbon films with excellent tribological and optical properties. as an innovation, variable angle spectroscopic ellipsometry (VASE) was successfully applied for non-destructive, 3-D, large-area tribological coatings quality investigation.;Based on the experience with the RFI PECVD system, a large-scale RFICP source was designed and built for the PSIL Langmuir probe and optical emission spectroscopy studies indicated …