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Articles 1 - 11 of 11

Full-Text Articles in Physics

Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel Oct 1998

Crystalline Surface Structures Induced By Ion Sputtering Of Al-Rich Icosahedral Quasicrystals, Z. Shen, Matthew J. Kramer, Cynthia J. Jenks, A. I. Goldman, Thomas A. Lograsso, D. Delaney, M. Heinzig, W. Raberg, Patricia A. Thiel

Chemistry Publications

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below ∼700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for ...


Island Size And Environment Dependence Of Adatom Capture: Cuyco Islands On Ru(0001), M. C. Bartelt, A. K. Schmid, James W. Evans, R. Q. Hwang Aug 1998

Island Size And Environment Dependence Of Adatom Capture: Cuyco Islands On Ru(0001), M. C. Bartelt, A. K. Schmid, James W. Evans, R. Q. Hwang

Mathematics Publications

We quantify the rate of capture by Co islands on Ru(0001) of additionally deposited Cu atoms, using scanning tunneling microscopy. The dependence of the capture rates on Co-island size is shown to reflect larger island-free areas surrounding bigger islands, a feature neglected in mean-field treatments. We also find a strong direction dependence in Cu adatom capture, reflecting the local environment of individual islands. These features are elucidated by simulations and diffusion equation analyses.


Ellipsometric And Kerr-Effect Studies Of Pt3−X (X=Mn,Co), R. J. Lange, S. J. Lee, David W. Lynch, Paul C. Canfield, Bruce N. Harmon, S. Zollner Jul 1998

Ellipsometric And Kerr-Effect Studies Of Pt3−X (X=Mn,Co), R. J. Lange, S. J. Lee, David W. Lynch, Paul C. Canfield, Bruce N. Harmon, S. Zollner

Physics and Astronomy Publications

The conductivity tensor of polycrystalline Pt3X (X=Mn,Co) was determined between 1.6 and 5.2 eV. Samples were arc melted, mechanically polished, and annealed at 500°C for 1 h in Ar. The complex dielectric function was measured from 1.3 to 5.2 eV at room temperature with a rotating analyzer ellipsometer. The magneto-optic Kerr effect was studied between 10 and 293 K in magnetic fields up to 3 T. We used the tight-binding linear-muffin-tin-orbital method in the local spin-density approximation to determine the band structure, density of states, and optical conductivity. Including an empirical quasiparticle self-energy ...


Finite Element Analysis Of The Influence Of A Fatigue Crack On Magnetic Properties Of Steel, Y. Shi, David C. Jiles Jun 1998

Finite Element Analysis Of The Influence Of A Fatigue Crack On Magnetic Properties Of Steel, Y. Shi, David C. Jiles

Center for Nondestructive Evaluation Publications

Fatigue can affect the magnetic properties of materials due to microstructural changes. Previous investigations have shown that several structure sensitive magnetic properties, such as coercivityHc and remanenceBr, changed systematically as a result of fatigue. When approaching failure the accumulated changes in microstructure resulted in the occurrence of fatigue cracks and the magnetic properties showed dramatic changes which mainly resulted from the geometrical changes in samples due to the cracks. It was found that the remanenceBr followed the changes in stress, while the coercivityHc sometimes showed different trends. In this article the influence of the size and the position of a ...


Domain-Wall Motion In Random Potential And Hysteresis Modeling, M. Pasquale, V. Basso, G. Bertotti, David C. Jiles, Y. Bi Jun 1998

Domain-Wall Motion In Random Potential And Hysteresis Modeling, M. Pasquale, V. Basso, G. Bertotti, David C. Jiles, Y. Bi

Ames Laboratory Publications

Two different approaches to hysteresis modeling are compared using a common ground based on energy relations, defined in terms of dissipated and stored energy. Using the Preisach model and assuming that magnetization is mainly due to domain-wall motion, one can derive the expression of magnetization along a major loop typical of the Jiles–Atherton model and then extend its validity to cases where mean-field effects and reversible contributions are present.


Hydrodynamic Limits For The Monomer-Dimer Surface Reaction: Chemical Diffusion, Wave Propagation, And Equistability, M. Tammaro, James W. Evans May 1998

Hydrodynamic Limits For The Monomer-Dimer Surface Reaction: Chemical Diffusion, Wave Propagation, And Equistability, M. Tammaro, James W. Evans

Mathematics Publications

For finite adspecies mobility, the lattice-gas monomer-dimer (A+B2) surface reaction model exhibits a discontinuous transition from a stable reactive steady state to a stable A-poisoned steady state, as the impingement rate PA for A increases above a critical value P*. The reactive (poisoned) state is metastable for PA just above (below) P*. Increasing the surface mobility of Aenhances metastability, leading to bistability in the limit of high mobility. In the bistable region, the more stable state displaces the less stable one separated from it by a planar interface, with P*becoming the equistability point for the two states. This ...


Reactive Removal Of Unstable Mixed No+Co Adlayers: Chemical Diffusion And Reaction Front Propagation, Michael Joseph Tammaro, James W. Evans May 1998

Reactive Removal Of Unstable Mixed No+Co Adlayers: Chemical Diffusion And Reaction Front Propagation, Michael Joseph Tammaro, James W. Evans

Mathematics Publications

A lattice-gas model is developed to describe the reactive removal of a preadsorbed, mixed NO+COadlayer covering a Pt(100) surface, via reduction of NO with CO, and behavior of the model is analyzed. Since NO dissociation requires an adjacent empty site, the NO+CO covered surface constitutes an unstable steady state. The creation of vacancies leads NO dissociation, the reaction of CO with the O formed by dissociation, the subsequent creation of more vacancies, and thus the autocatalytic removal of the adlayer. The high mobility of most adspecies leads to an initial “disperse stage” of adlayer removal, characterized by ...


Fivefold Surface Of Quasicrystalline Alpdmn: Structure Determination Using Low-Energy-Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, P. J. Pinhero, Cynthia J. Jenks, James W. Anderegg, C.-M. Zhang, Patricia A. Thiel Apr 1998

Fivefold Surface Of Quasicrystalline Alpdmn: Structure Determination Using Low-Energy-Electron Diffraction, M. Gierer, M. A. Van Hove, A. I. Goldman, Z. Shen, S.-L. Chang, P. J. Pinhero, Cynthia J. Jenks, James W. Anderegg, C.-M. Zhang, Patricia A. Thiel

Chemistry Publications

The atomic structure of the fivefold symmetric quasicrystal surface of icosahedral AlPdMn has been investigated by means of a dynamical low-energy-electron diffraction (LEED) analysis. Approximations were developed to make the structure of an aperiodic, quasicrystalline surface region accessible to LEED theory. A mix of several closely similar, relaxed, bulklike lattice terminations is favored, all of which have a dense Al-rich layer on top followed by a layer with a composition of about 50% Al and 50% Pd. The interlayer spacing between these two topmost layers is contracted from the bulk value by 0.1 Å, to a final value of ...


Nuclear Battery, Howard R. Shanks Feb 1998

Nuclear Battery, Howard R. Shanks

Iowa State University Patents

A nuclear battery for supplying low level electrical energy for a relatively long period of time. The battery includes a low-energy beta emitter and phosphor dispersed sufficient proximate the beta emitter to capture the low energy betas before decay. A photovoltaic receptor is configured to have a peaked response near the wavelength of the photons emitted by the phosphor. In a preferred embodiment, the photovoltaic, phosphor and beta source are formed into flexible layers which are rolled into a cylinder in order to maximize the capture of photons emitted by the beta-excited phosphor


Clustered, Terraced And Mixed Surface Phases Of The Al70pd21mn9 Quasicrystal, J. Ledieu, A. W. Munz, T. M. Parker, R. Mcgrath, R. D. Diehl, Dwight W. Delaney, Thomas A. Lograsso Jan 1998

Clustered, Terraced And Mixed Surface Phases Of The Al70pd21mn9 Quasicrystal, J. Ledieu, A. W. Munz, T. M. Parker, R. Mcgrath, R. D. Diehl, Dwight W. Delaney, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

The five-fold surface of the Al70 Pd21 Mn9 quasicrystal has been studied using STM, LEED and AES. STM images from surfaces which have been sputtered and annealed to 875 K reveal 20-30 Å protrusions that have been identified by others as Mackay-type clusters. Higher-resolution images reveal substructures in these clusters having dimensions 2-3 Å. Longer annealing times at 875 K produced large areas having flat terraces which were imaged with atomic resolution. The LEED pattern from this surface has sharp spots on a low background, and AES indicates that the surface is deficient in Mn relative to ...


Chemical Diffusivity And Wave Propagation In Surface Reactions: Lattice-Gas Model Mimicking Co-Oxidation With High Co-Mobility, Michael Joseph Tammaro, James W. Evans Jan 1998

Chemical Diffusivity And Wave Propagation In Surface Reactions: Lattice-Gas Model Mimicking Co-Oxidation With High Co-Mobility, Michael Joseph Tammaro, James W. Evans

Mathematics Publications

We analyze the spatiotemporal behavior in a lattice-gas model for the monomer-dimer reaction on surfaces. This model, which mimics catalytic CO-oxidation, includes a mobilemonomer adspecies (representing CO), an immobile dissociatively adsorbed dimer species (representing O), and afinitereaction rate (for CO2 production). We characterize in detail the propagation of the chemical wave or reaction front produced when the stable reactive steady-state of the model displaces the metastable CO-poisoned state. In the regime of high CO-mobility, such propagation can be described directly within a “hydrodynamic” reaction-diffusion equation formalism. However, we show that the chemical diffusivity of CO is dependent ...