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Full-Text Articles in Physics

Optical Properties And Electronic Structures Of The Intermetallic Compounds Auga2 And Ptga2, Kwang-Joo Kim, Bruce N. Harmon, Liang-Yao Chen, David W. Lynch Nov 1990

Optical Properties And Electronic Structures Of The Intermetallic Compounds Auga2 And Ptga2, Kwang-Joo Kim, Bruce N. Harmon, Liang-Yao Chen, David W. Lynch

Physics and Astronomy Publications

The electronic structures of AuGa2 and PtGa2 have been studied with use of spectroscopic ellipsometry and the dielectric functions have been determined in the 1.2–5.5-eV region. Both compounds show interband absorption at low photon energies (<1.3 eV). The interband absorption for AuGa2 is strong at about 2 eV while that for PtGa2 shows a broad structure in the range 2.5–4.5 eV, with a shoulder at 3.3 eV. The observed interband features in ε2 can be interpreted in terms of self-consistent relativistic band-structure calculations using the linear augmented-plane-wave method. The interband contribution to the imaginary part of the dielectric function εb2 has been calculated including the effect of the electric dipole matrix elements. The overall agreement is good between the band calculations and the ellipsometry results in the 1.2–5.5-eV region for both the magnitude and the positions of the structures. Below 1.2 eV the calculational results for both compounds show interband absorption, which is also qualitatively suggested by the ellipsometry results.


Photoemission Study Of Au On A-Si:H, Tun-Wen Pi, A.-B. Yang, C. G. Olson, David W. Lynch Nov 1990

Photoemission Study Of Au On A-Si:H, Tun-Wen Pi, A.-B. Yang, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

We report a high-resolution photoemission study of Au evaporated on rf-sputtered a-Si:H at room temperature. Three regions of coverage can be classified according to the behavior of the valence-band and core-level spectra: an unreacted region with an equivalent thickness of 2 Å, followed by an intermixed Au/a-Si overlayer (∼9 Å), and a dual-phase region at higher coverage. Au adatoms are dispersed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen bonded, suggesting that the intermixed Si is mainly from those that have dangling bonds ...


Photoemission Study Of Cr On A-Si:H, Tun-Wen Pi, C. G. Olson, David W. Lynch Nov 1990

Photoemission Study Of Cr On A-Si:H, Tun-Wen Pi, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

We report a synchrotron-radiation photoemission study of Cr evaporated on rf-sputtered a-Si:H at room temperature. The evolution of the interface qualitatively follows that on c-Si, despite differences in the valence-band emission. The interface begins with an inactive layer (≤1 Å) of Cr, followed by an intermixed Cr/a-Si:H layer (≤12 Å). With further Cr deposition, bulklike Cr metal begins to develop on top of these. Some features exhibited by the Cr/a-Si:H interface are specific to a-Si:H surfaces. For instance, Cr adatoms are found around the dangling-bond neighborhood at coverages below ...


High-Resolution Angle-Resolved Photoemission Study Of The Fermi Surface And The Normal-State Electronic Structure Of Bi2sr2cacu2o8, C. G. Olson, R. Liu, David W. Lynch, R. S. List, A. J. Arko, B. W. Veal, Y. C. Chang, P. Z. Jiang, A. P. Paulikas Jul 1990

High-Resolution Angle-Resolved Photoemission Study Of The Fermi Surface And The Normal-State Electronic Structure Of Bi2sr2cacu2o8, C. G. Olson, R. Liu, David W. Lynch, R. S. List, A. J. Arko, B. W. Veal, Y. C. Chang, P. Z. Jiang, A. P. Paulikas

Physics and Astronomy Publications

High-resolution angle-resolved photoelectron spectroscopic measurements were made of the Fermi edge of a single crystal of Bi2Sr2CaCu2O8 at 90 K along several directions in the Brillouin zone. The resultant Fermi-level crossings are consistent with local-density band calculations, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250 K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level the spectra show correlation effects in the form of an increased effective mass, but the essence ...


Ce-Catalyzed Oxidation Of Ta(110), C. Gu, David W. Lynch, A. B. Yang, C. G. Olson Jul 1990

Ce-Catalyzed Oxidation Of Ta(110), C. Gu, David W. Lynch, A. B. Yang, C. G. Olson

Physics and Astronomy Publications

Photoemission spectroscopy was used to investigate the initial oxidation of the Ce/Ta(110) interface at room temperature. The oxidation of Ta(110) is dramatically enhanced by a thin Ce overlayer. A Ta suboxide TaOχ (0.5≤χ≤1) is formed first in the interface, followed by the rapid formation of Ta2O5 upon further oxygen exposure. A weak interface reaction exists in Ce/Ta(110), but is excluded as the main cause of the catalytic oxidation. An earlier suggestion is reconfirmed that the Ce layer converts O2 to oxygen ions and thus promotes the oxidation of the substrate.


Inverse-Photoemission Measurement Of Iron Oxides On Polycrystalline Fe, Bong-Soo Kim, Sayong Hong, David W. Lynch Jun 1990

Inverse-Photoemission Measurement Of Iron Oxides On Polycrystalline Fe, Bong-Soo Kim, Sayong Hong, David W. Lynch

Physics and Astronomy Publications

We measured the inverse-photoemission spectra (IPES) of iron oxides grown on an Fe substrate and calculated the band structure of paramagnetic FeO to analyze the IPES. The band-structure calculation showed some overlap between Fe 3d states and O 2p states in the region of occupied states, and s,p-like states of Fe in the unoccupied region. Isochromatic IPES showed two structures at ∼2.5 and ∼7.5 eV above the Fermi energy. We estimated from the IPES data a full band gap of 2.5 eV for FeO.


Interpretation Of The Magnetization Mechanism In Terfenol‐D Using Barkhausen Pulse‐Height Analysis And Irreversible Magnetostriction, David C. Jiles, S. Hariharan May 1990

Interpretation Of The Magnetization Mechanism In Terfenol‐D Using Barkhausen Pulse‐Height Analysis And Irreversible Magnetostriction, David C. Jiles, S. Hariharan

Electrical and Computer Engineering Publications

The ternary alloy Dy0.7Tb0.3Fe1.9, known as Terfenol‐D, is a highly magnetostrictive alloy with magnetostriction coefficients along the principal crystallographic directions of λ1 1 1=1640×10−6and λ1 0 0≤100(±30)×10−6. The bulk magnetostriction λ is dependent on the state of magnetization M, on the original domain configuration, and on the texture of the material. This paper reports on Barkhausen measurements and magnetostriction. The pulse‐height distribution of Barkhausen emissions revealed events occurring at a specific amplitude which were stress dependent. The magnetostriction results gave ...


Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo Mar 1990

Low-Temperature Epitaxial Growth Of Thin Metal Films, James W. Evans, D. E. Sanders, Patricia A. Thiel, Andrew E. Depristo

Chemistry Publications

We present a different mechanism to explain the occurrence of long-lived oscillations in diffraction spot intensities during epitaxial growth of metal films on fcc (100) substrates at low temperature. Rather than rely on the common picture of cyclical nucleation and growth to produce the oscillations, the model invokes ‘‘downward funneling’’ deposition dynamics to fourfold-hollow adsorption sites.


Diffusion Of Noninteracting Particles Into A Semi-Infinite Lattice, James W. Evans Jan 1990

Diffusion Of Noninteracting Particles Into A Semi-Infinite Lattice, James W. Evans

Physics and Astronomy Publications

Consider a gas of noninteracting particles diffusing into a semi-infinite lattice, Z+×ZD−1, subject to exclusion of double occupancy. An exact closed set of equations can be obtained and solved (in closed form) for the single-site occupancies or densities. Equations for the n-site occupancies couple only to such functions for n and n-1 sites, as for an infinite lattice. Their analysis reveals that negative pair correlations develop during this process, reflecting the propensity for diffusion to reduce density inhomogeneities and fluctuations.


Cluster Diffusivity: Structure, Correlation, And Scaling, H. C. Kang, P. A. Thiel, James W. Evans Jan 1990

Cluster Diffusivity: Structure, Correlation, And Scaling, H. C. Kang, P. A. Thiel, James W. Evans

Physics and Astronomy Publications

We have investigated the diffusion of clusters on a triangular lattice using Monte Carlo simulations. A cluster is defined as a two‐dimensional collection of particles which are connected to each other, either directly or indirectly through other particles in the cluster, by nearest‐neighbor bonds. Each particle is allowed to hop, with probability αδb/2/(α−δb/2+αδb/2), to a vacant nearest‐neighbor site with the constraint that the hop does not break the cluster. The change in the number of bonds is given by δb. The equilibrium clusters are correlated animals with ...


Inequivalent Models Of Irreversible Dimer Filling: ‘‘Transition State’’ Dependence, R. S. Nord, James W. Evans Jan 1990

Inequivalent Models Of Irreversible Dimer Filling: ‘‘Transition State’’ Dependence, R. S. Nord, James W. Evans

Physics and Astronomy Publications

Irreversible adsorption of diatomics on crystalline surfaces is sometimes modeled as random dimer filling of adjacent pairs of sites on a lattice. We note that this process can be implemented in two distinct ways: (i) randomly pick adjacent pairs of sites,  jj’, and fill  jj’ only if both are empty (horizontal transition state); or (ii) randomly pick a single site,  j, and if  j and at least one neighbor are empty, then fill  j and a randomly chosen empty neighbor (vertical transition state). Here it is instructive to consider processes which also include competitive random monomer filling of ...