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Full-Text Articles in Physics

Analysis Of Primary Stripper Foils At The Spallation Neutron Source By An Electron Beam Foil Test Stand, Eric Paul Barrowclough Dec 2017

Analysis Of Primary Stripper Foils At The Spallation Neutron Source By An Electron Beam Foil Test Stand, Eric Paul Barrowclough

Doctoral Dissertations

Diamond films are used at the Spallation Neutron Source (SNS) as the primary charge exchange foils (i.e., stripper foils) of the accelerated 1 GeV (Gigaelectron volts) hydride ions. The most common type of film used is a nanocrystalline diamond film, typically 17 mm x 45 mm (millimeter) with an aerial density of 350 μg/cm2 (microgram per square centimeter). The diamond film is deposited on a corrugated silicon substrate using plasma-assisted chemical vapor deposition. After the growth of the diamond film, 30 mm of the silicon substrate is etched away, leaving a freestanding diamond foil with a silicon ...


Electronic And Magnetic Materials Under External Stimuli, Kenneth Robert O'Neal Aug 2017

Electronic And Magnetic Materials Under External Stimuli, Kenneth Robert O'Neal

Doctoral Dissertations

The interaction between spin, charge, and lattice degrees of freedom leads to exotic and useful properties in multifunctional materials. This delicate balance of energy scales allows external stimuli such as temperature, magnetic field, or pressure to drive to novel phases. As a local probe technique, spectroscopy can provide insight into the microscopic mechanism of the phase transitions. In this dissertation I present spectroscopic studies of functional materials under extreme conditions.

Nanomaterials have attracted attention because nanoscale confinement affects various material properties and often reduces energy scales or suppress phase transitions. Combining Raman and infrared spectroscopies reveals that the breakdown mechanism ...


Understanding Three-Body Interactions In Hexagonal Close Packed Solid He-4, Ashleigh Locke Barnes May 2017

Understanding Three-Body Interactions In Hexagonal Close Packed Solid He-4, Ashleigh Locke Barnes

Doctoral Dissertations

The ground state properties of hexagonal close packed (hcp) solid 4He [He-4] are dominated by large atomic zero point motions which make the primary contribution to the solid’s low-temperature Debye-Waller (DW) factors. Preliminary investigations have also suggested that three-body interactions can play an important role in this system, particularly at higher densities. However, due to their computational cost, these interactions are not generally incorporated into theoretical models of solid 4He [He-4]. In order to accurately treat both zero point motion and three-body interactions, we have developed a perturbative treatment in which the three-body energy is added as ...


Investigating The Properties Of Superfluid He-4 Through Density Functional Calculations, Matthew Francis Dutra May 2017

Investigating The Properties Of Superfluid He-4 Through Density Functional Calculations, Matthew Francis Dutra

Doctoral Dissertations

We present a study of isotopically pure He-4 systems evaluated using helium density functional theory (He-DFT) with the intent of better understanding their ground state structural and energetic properties, particularly within the scope of singularly-doped helium droplets. We self-consistently solve for the density profiles and chemical potentials for a wide range of pure helium droplet sizes (up to 9500 atoms) via an imaginary time propagation method, and fit the resultant energetic data to a power law formula to be able to extrapolate values for even larger droplets. Subsequent calculations on singularly-doped droplets within the same size range yield accurate binding ...


Understanding The Plasmonic Properties Of Metallic Nanostructures With Correlated Photon- And Electron-Driven Excitations, Vighter Ozezinimize Iberi May 2014

Understanding The Plasmonic Properties Of Metallic Nanostructures With Correlated Photon- And Electron-Driven Excitations, Vighter Ozezinimize Iberi

Doctoral Dissertations

The collective oscillation of the conduction band electrons in metal nanostructures, known as plasmons, can be used to manipulate light on length scales that are smaller than the diffraction limit of visible light. In this dissertation, a correlated approach is used to probe localized surface plasmon resonances (LSPRs) in metallic nanostructures, and their application to surface-enhanced spectroscopy. This correlated approach involves the measurement of LSPRs with dark-field optical microscopy (resonance-Rayleigh scattering), and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Structural parameters of the exact same nanostructures obtained from the STEM are subsequently used in performing fully ...


Magneto-Optical Properties Of Complex Oxides, Peng Chen Dec 2013

Magneto-Optical Properties Of Complex Oxides, Peng Chen

Doctoral Dissertations

Complex oxides give rise to rich physics and exotic cross-coupled electronic and magnetic properties. This is because of the competing interaction between charge, structure, and magnetism in the materials. In this dissertation I present a spectroscopic investigation of several model complex oxides under external stimuli of magnetic field and temperature. The compounds of interest include BiFeO3 [bismuth ferrite] nanoparticles and tetragonal film, Bi1-xNdxFeO3 [neodymium doped bismuth ferrite], α-Fe2O3 [hematite], Ni3V2O8 [nickel vanadate], and RIn1-xMnxO3 [manganese doped rare earth indium oxide ...


Alkane Adsorption On Mgo(100): Volumetric Isotherm, Inelastic Neutron Scattering, And Computational Studies, Andrew Spencer Hicks May 2013

Alkane Adsorption On Mgo(100): Volumetric Isotherm, Inelastic Neutron Scattering, And Computational Studies, Andrew Spencer Hicks

Doctoral Dissertations

Volumetric adsorption isotherms and computational molecular dynamics (MD) simulations were performed for nonane and decane adfilms on MgO(100) nanocubes. From the isotherms, variety of thermodynamic quantities are calculated. These values, along with visual inspection of the isotherms, indicate a layer by layer trend from 2D to 3D behavior. This is attributed to the increasing importance of vertical adsorbate-adsorbate interactions as distance from the surface increases. Additionally, a 2D phase transition is observed for the first adsorbed layer as indicated by the evolution of the widths of the isotherm first derivative peaks. These experimental results are complemented by the MD ...


Confinement Effects Of Solvation On A Molecule Physisorbed On A Metal Particle, Jacob Fosso Tande Dec 2012

Confinement Effects Of Solvation On A Molecule Physisorbed On A Metal Particle, Jacob Fosso Tande

Doctoral Dissertations

We describe and present results of the implementation of the surface and volume polarization for electrostatics~(SVPE) and the iso-density surface solvation models. Unlike most other implementation of the solvation models where the solute and the solvent are described with multiple numerical representation, our implementation uses a multiresolution, adaptive multiwavelet basis to describe both solute and the solvent. This requires reformulation to use integral equations throughout as well as a conscious management of numerical properties of the basis.

Likewise, we investigate the effects of solvation on the static properties of a molecule physisorbed on a spherical particle, modeled as a ...


Charge, Bonding, And Magneto-Elastic Coupling In Nanomaterials, Qi Sun Dec 2012

Charge, Bonding, And Magneto-Elastic Coupling In Nanomaterials, Qi Sun

Doctoral Dissertations

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials because they are intimately connected to charge, structure, and magnetism, and a quantitative analysis of their behavior can reveal microscopic aspects of chemical bonding and spin-phonon coupling. To investigate these effects, we measured infrared vibrational properties of bulk and nanoscale MoS2 [molybdenum disulfide], MnO [manganese(II) oxide], and CoFe2O4 [cobalt iron oxide]. From an analysis of frequencies, oscillator strengths, and high-frequency dielectric constants, we extracted Born and local effective charges, and polarizability for MoS2 and MnO. For MoS2 nanoparticles ...


Direct Observation Of H2 Binding To A Metal Oxide Surface, J. Z. Larese, T. Arnold, L. Frazier, R. J. Hinde, A. J. Ramirez-Cuesta Oct 2008

Direct Observation Of H2 Binding To A Metal Oxide Surface, J. Z. Larese, T. Arnold, L. Frazier, R. J. Hinde, A. J. Ramirez-Cuesta

Chemistry Publications and Other Works

Inelastic neutron scattering is used to probe the dynamical response of H2 films adsorbed on MgO(100) as a function of film thickness. Concomitant diffraction measurements and a reduced-dimensionality quantum dynamical model provide insight into the molecule-surface interaction potential. At monolayer thickness, the rotational motion is strongly influenced by the surface, so that the molecules behave like quasiplanar rotors. These findings have a direct impact on understanding how molecular hydrogen binds to the surface of materials used in catalytic and storage applications.


A Six-Dimensional H2–H2 Potential Energy Surface For Bound State Spectroscopy, Robert Hinde Jan 2008

A Six-Dimensional H2–H2 Potential Energy Surface For Bound State Spectroscopy, Robert Hinde

Chemistry Publications and Other Works

We present a six-dimensional potential energy surface for the (H2)2 dimer based on coupled-cluster electronic structure calculations employing large atom-centered Gaussian basis sets and a small set of midbond functions at the dimer’s center of mass. The surface is intended to describe accurately the bound and quasibound states of the dimers (H2)2, (D2)2, and H2–D2 that correlate with H2 or D2 monomers in the rovibrational levels (v, j) =(0,0), (0,2), (1,0), and (1,2). We employ a close-coupled approach to compute the energies of these ...


Interaction-Induced Dipole Moment Of The Ar–H2 Dimer: Dependence On The H2 Bond Length, Robert J. Hinde Jan 2006

Interaction-Induced Dipole Moment Of The Ar–H2 Dimer: Dependence On The H2 Bond Length, Robert J. Hinde

Chemistry Publications and Other Works

We present ab initio calculations of the interaction-induced dipole moment of the Ar–H2 van der Waals dimer. The primary focus of our calculations is on the H2 bond length dependence of the dipole moment, which determines the intensities of both the collision-induced H2 = 1 ← 0 fundamental band in gaseous Ar–H2 mixtures and the dopant-induced H2 = 1 ← 0 absorption feature in Ar-doped solid H2 matrices. Our calculations employ large atom-centered basis sets, diffuse bond functions positioned between the two monomers, and a coupled cluster treatment of valence electron correlation; core-valence correlation effects appear ...


Population Size Bias In Descendant-Weighted Diffusion Quantum Monte Carlo Simulations, G. Lee Warren, Robert J. Hinde Jan 2006

Population Size Bias In Descendant-Weighted Diffusion Quantum Monte Carlo Simulations, G. Lee Warren, Robert J. Hinde

Chemistry Publications and Other Works

We consider the influence of population size on the accuracy of diffusion quantum Monte Carlo simulations that employ descendant weighting or forward walking techniques to compute expectation values of observables that do not commute with the Hamiltonian. We show that for a simple model system, the d-dimensional isotropic harmonic oscillator, the population size must increase rapidly with d in order to ensure that the simulations produce accurate results. When the population size is too small, expectation values computed using descendant-weighted diffusion quantum Monte Carlo simulations exhibit significant systematic biases.


Vibrational Dependence Of The H2–H2 C6 Coefficients, Robert Hinde Jan 2005

Vibrational Dependence Of The H2–H2 C6 Coefficients, Robert Hinde

Chemistry Publications and Other Works

We use the sum-over-states formalism to compute the imaginary-frequency dipole polarizabilities for H2, as a function of the H–H bond length, at the full configuration interaction level of theory using atom-centered d-aug-cc-pVQZ basis sets. From these polarizabilities, we obtain isotropic and anisotropic C6 dispersion coefficients for a pair of H2 molecules as functions of the two molecules’ bond lengths.


Infrared-Active Vibron Bands Associated With Substitutional Impurities In Solid Parahydrogen, Robert Hinde Jan 2003

Infrared-Active Vibron Bands Associated With Substitutional Impurities In Solid Parahydrogen, Robert Hinde

Chemistry Publications and Other Works

We present a model for the line shapes of infrared-active Q1(0) vibron bands observed in solid parahydrogen doped with low concentrations of spherical substitutional impurities. The line shapes are highly sensitive to the H2 vibrational dependence of the dopant–H2 interaction. When this vibrational dependence is strong, the dopant can trap the infrared-active vibron in its first solvation shell; in this case, the trapped vibron manifests itself in the absorption spectrum as a narrow feature to the red of the pure solid’s vibron band.


The He-Lih Potential Energy Surface Revisited. I. An Interpolated Rigid Rotor Surface, Robert Hinde Jan 1999

The He-Lih Potential Energy Surface Revisited. I. An Interpolated Rigid Rotor Surface, Robert Hinde

Chemistry Publications and Other Works

We reconsider the potential energy surface of the He–LiH system recently examined by Gianturco and co-workers [F. A. Gianturco et al., Chem. Phys. 215, 227 (1997)]. We compute the He–LiH interaction energy at the CCSD(T) level using large correlation consistent atomic basis sets supplemented with bond functions. To capture the severe anisotropy of the He–LiH potential, we interpolate our ab initio points in the angular direction with cubic splines, then expand the splines in terms of Legendre polynomials. The resulting smooth potential surface differs substantially from that of Gianturco et al.; in particular, our attractive He ...