Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 4 of 4

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 ...


Charge-Correlation Effects In Calculations Of Atomic Short-Range Order In Metallic Alloys, F. J. Pinksi, J. B. Staunton, Duane D. Johnson Jun 1998

Charge-Correlation Effects In Calculations Of Atomic Short-Range Order In Metallic Alloys, F. J. Pinksi, J. B. Staunton, Duane D. Johnson

Duane D. Johnson

The “local” chemical environment that surrounds an atom directly influences its electronic charge density. These atomic charge correlations play an important role in describing the Coulomb and total energies for random substitutional alloys. Although the electronic structure may be well represented by a single-site theory, such as the coherent potential approximation, the electrostatic energy is not as well represented when these charge correlations are ignored. For metals, including the average effect from the charge correlation coming from only the nearest-neighbor shell has been shown to be sufficient to determine accurately the energy of formation. In this paper, we incorporate such ...


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 ...


Metallic Photonic Band Gap Structures On Flexible Substrates , Sandhya Gupta Jan 1998

Metallic Photonic Band Gap Structures On Flexible Substrates , Sandhya Gupta

Retrospective Theses and Dissertations

Periodic dielectric and metallic structures have recently generated great interest because they can exhibit a forbidden range of frequency, or a photonic band gap (PBG) where the electromagnetic waves cannot propagate. Since their theoretical prediction in 1987, several applications at frequencies ranging from microwave to optical region have been proposed using these novel structures. This presentation demonstrates the first successful fabrication of flexible metallic PBG structures that show frequency filtering properties at far-infrared frequencies;The metallic PBG filters described here are multi-layered metallic meshes imbedded in a flexible polyimide dielectric. They have a simple, microfabrication-based construction that use alternating dielectric ...