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2003

Brigham Young University

Articles 1 - 13 of 13

Full-Text Articles in Physics

Long Coherence Times At 300 K For Nitrogen-Vacancy Center Spins In Diamond Grown By Chemical Vapor Deposition, John S. Colton, T. A. Kennedy, J. E. Butler, R. C. Linares, P.J. Doering Nov 2003

Long Coherence Times At 300 K For Nitrogen-Vacancy Center Spins In Diamond Grown By Chemical Vapor Deposition, John S. Colton, T. A. Kennedy, J. E. Butler, R. C. Linares, P.J. Doering

Faculty Publications

Electron-spin-echo experiments reveal phase-memory times as long as 58 μs at 300 K for nitrogen-vacancy centers in chemical vapor deposition (CVD) single crystals. The spins were optically polarized and optically detected. Two high-quality CVD samples were studied. From the current results, it is not clear whether these phase-memory times represent a fundamental limit or are limited by an external source of decoherence.

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Ordering Tendencies In Octahedral Mgo-Zno Alloys, Gus L. W. Hart, Mahdi Sanati, Alex Zunger Oct 2003

Ordering Tendencies In Octahedral Mgo-Zno Alloys, Gus L. W. Hart, Mahdi Sanati, Alex Zunger

Faculty Publications

Isostrutural II-VI alloys whose components are either rocksalt stable (e.g., CaO-MgO) or zincblende stable (e.g., ZnS-ZnSe) are known to be thermodynamically unstable at low temperatures, showing a miscibility gap and no bulk ordering. In contrast, we show that heterostructural MgO-ZnO is stable, under certain conditions, in the sixfold-coordinated structure for Zn concentrations below 67%, giving rise to spontaneously ordered alloys. Using first-principles calculations, we explain the origin of this stability, the structures of their low-temperature ordered phases, short-range-order patterns, and their optical band-gap properties.

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Allowed Mesoscopic Point Group Symmetries In Domain Average Engineering Of Perovskite Ferroelectric Crystals, Dorian M. Hatch, H. T. Stokes, W. Cao Oct 2003

Allowed Mesoscopic Point Group Symmetries In Domain Average Engineering Of Perovskite Ferroelectric Crystals, Dorian M. Hatch, H. T. Stokes, W. Cao

Faculty Publications

In multivariant systems, several energetically degenerate low temperature domain states can be produced at the structural phase transition. Coexistence of these domain states can produce mesoscopic structures that possess symmetries distinct from the microscopic single domain crystal symmetry. Such engineered domain structures in certain ferroelectric materials have been proven to give superior piezoelectric properties and extremely soft shear moduli. The objective of this article is to consider the variety of symmetries that can be produced through domain average engineering in proper ferroelectric systems arising from the cubic Pm[overline 3]m symmetry perovskite structure.

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First-Principles Calculations For Nitrogen-Containing Single-Walled Carbon Nanotubes, James P. Lewis, Mingwen Zhao, Yueyugan Xia, Ruiqin Zhang Aug 2003

First-Principles Calculations For Nitrogen-Containing Single-Walled Carbon Nanotubes, James P. Lewis, Mingwen Zhao, Yueyugan Xia, Ruiqin Zhang

Faculty Publications

We present calculations for possible configurations of nitrogen-containing single-walled carbon nanotubes and their electronic properties obtained with the ab initio tight-binding FIREBALL method. It is found that nitrogen atoms can be energetically incorporated into the carbon network in three forms: Substitution, substitution with formation of a vacancy structure, and chemical adsorption. The different forms exhibit different local densities of states near the Fermi levels, which might suggest a potential method to control the electronic properties of nitrogen-doped carbon nanotubes

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Multienergetic External-Beam Pixe As A Means Of Stydying The Surface Enrichment Effect In Coins, Scott Evans Perry Jul 2003

Multienergetic External-Beam Pixe As A Means Of Stydying The Surface Enrichment Effect In Coins, Scott Evans Perry

Theses and Dissertations

This thesis paper examines the feasibility of using external-beam PIXE to study the surface enrichment effect in metal artifacts. By varying the energy of the incident proton beam, we penetrated the artifact's surface to different levels and were able to produce a depth profile of the elemental composition of the sample. In this study, the sample set we chose to examine consisted of ancient and modern coins. This paper first describes the surface enrichment effect and theoretically how PIXE can be used to study it. It then details the construction of the components of the external-beam setup. Many of the …

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Observation Of And Model For Nonlinear Mode Conversion In A Non-Neutral Plasma, Grant W. Hart, Bryan G. Peterson, Ross L. Spencer Jul 2003

Observation Of And Model For Nonlinear Mode Conversion In A Non-Neutral Plasma, Grant W. Hart, Bryan G. Peterson, Ross L. Spencer

Faculty Publications

The nonlinear interaction of the two lowest Trivelpiece-Gould modes in a non-neutral plasma has been observed. Because of coupling in the nonlinear terms of the continuity and momentum equations, the two modes can exchange energy and convert one to the other. This can be modeled using the cold fluid equations and the averaging method. Experimentally, this process always stops with the lower frequency mode dominating the final state. Numerical integration of the model suggests that this occurs because the higher frequency mode is more strongly damped than the lower frequency mode.

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Iteration Methods For Approximating The Lowest Order Energy Eigenstate Of A Given Symmetry For One- And Two-Dimensional Systems, Chad Everett Junkermeier Jun 2003

Iteration Methods For Approximating The Lowest Order Energy Eigenstate Of A Given Symmetry For One- And Two-Dimensional Systems, Chad Everett Junkermeier

Theses and Dissertations

Using the idea that a quantum mechanical system drops to its ground state as its temperature goes to absolute zero several operators are devised to enable the approximation of the lowest order energy eigenstate of a given symmetry; as well as an approximation to the energy eigenvalue of the same order.

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Decay Of Trapped-Particle Asymmetry Modes In Non-Neutral Plasmas In A Malmberg-Penning Trap, Grant W. Mason May 2003

Decay Of Trapped-Particle Asymmetry Modes In Non-Neutral Plasmas In A Malmberg-Penning Trap, Grant W. Mason

Faculty Publications

The mechanism for the strong damping of diocotron-like azimuthal trapped-particle asymmetry modes in a Malmberg-Penning trap is investigated with a detailed three-dimensional particle-in-cell computer simulation. The m = 1,kzis not equal to 0 modes are created by a voltage squeeze from a mid-detector ring followed by a displacement of trapped particles in opposite directions on either side of the ring. The voltage squeeze creates a population of particles confined to half the trap length (trapped) and a population of particles that move longitudinally along the full length of the cylinder (untrapped). The damping of the modes is found to be …

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Optically Oriented And Detected Electron Spin Resonance In A Lightly Doped N-Gaas Layer, John S. Colton, T. A. Kennedy, A. S. Bracker, D. Gammon, J. B. Miller Apr 2003

Optically Oriented And Detected Electron Spin Resonance In A Lightly Doped N-Gaas Layer, John S. Colton, T. A. Kennedy, A. S. Bracker, D. Gammon, J. B. Miller

Faculty Publications

Spin resonance of localized electrons bound to donors in a specially designed n-GaAs layer has been performed at 236 MHz and 41 mT, using circular polarized light to polarize the electrons and photoluminescence to detect the electronic polarization. The polarization was diminished under the resonance condition. The electronic g factor obtained by this measurement is - 0.41 ± 0.01. The resonance linewidth of 2 mT corresponds to a spin lifetime of 28 ns. In order to observe the electronic spin resonance, nuclear effects were eliminated by application of rf fields to simultaneously resonate the nuclear spins.

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Modes In A Non-Neutral Plasma Of Finite Length, M = 0,1, S. Neil Rasband, Ross L. Spencer Apr 2003

Modes In A Non-Neutral Plasma Of Finite Length, M = 0,1, S. Neil Rasband, Ross L. Spencer

Faculty Publications

For realistic, cold equilibria of finite length representing a pure electron plasma confined in a cylindrical Malmberg–Penning trap, the mode spectrum for Trivelpiece–Gould, m=0, and for diocotron, m=1, modes is calculated numerically. A novel method involving finite elements is used to successfully compute eigenfrequencies and eigenfunctions for plasma equilibria shaped like pancakes, cigars, long cylinders, and all things in between. Mostly sharp-boundary density configurations are considered but also included in this study are diffuse density profiles including ones with peaks off axis leading to instabilities. In all cases the focus has been on elucidating the role of finite length in …

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What The Universe Means To People Like Me, David D. Allred Mar 2003

What The Universe Means To People Like Me, David D. Allred

Faculty Publications

When I picked up David's paper to read it, I had a pencil in my hand. Years of reading my students' and my own papers made it natural to edit as I read. However, I heard in my mind the voice of my mother advising me to put the pencil down. This wasn't time to edit but to hear and understand. Still, I kept the pencil in my hand for the first few pages and made a few notes before I put it down and just read. I could hear David's voice speaking the words I read. It was good …

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Neutral-Plasma Oscillations At Zero Temperature, Scott D. Bergeson, Ross L. Spencer Feb 2003

Neutral-Plasma Oscillations At Zero Temperature, Scott D. Bergeson, Ross L. Spencer

Faculty Publications

Cold plasma theory is used to calculate the response of an ultracold neutral plasma to an applied rf field. The free oscillation of the system has a continuous spectrum and an associated damped quasimode. This quasimode dominates the driven response and is resonant in the tail of the density distribution. Recent experiments used the plasma response to an applied rf field to determine the plasma density in an expanding ultracold plasma. The comparison between experiment and theory indicates that this method accurately determines the expansion velocity and underestimates the initial plasma density by a factor of 3 in weakly collisional …

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Chemomechanical Surface Patterning And Functionalization Of Silicon Surfaces Using An Atomic Force Microscope, Brent A. Wascaser, Michael J. Maughan, Travis L. Niederhauser, Matthew R. Linford, Robert C. Davis, Ian A. Mowat Feb 2003

Chemomechanical Surface Patterning And Functionalization Of Silicon Surfaces Using An Atomic Force Microscope, Brent A. Wascaser, Michael J. Maughan, Travis L. Niederhauser, Matthew R. Linford, Robert C. Davis, Ian A. Mowat

Faculty Publications

Surface modification and patterning at the nanoscale is a frontier in science with significant possible applications in biomedical technology and nanoelectronics. Here we show that an atomic force microscope (AFM) can be employed to simultaneously pattern and functionalize hydrogen-terminated silicon (111) surfaces. The AFM probe was used to break Si-H and Si-Si bonds in the presence of reactive molecules, which covalently bonded to the scribed Si surface. Functionalized patches and patterned lines of molecules were produced. Linewidths down to 30 nm were made by varying the force at the tip

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