Observation of a Cs-induced state in the band gap of GaP(110): Alkali-metal bonding and Fermi-level pinning

The deposition of submonolayer quantities of Cs onto GaP(110) causes strong photoemission features in the region of the semiconductor fundamental band gap. This observation is interpreted in terms of emission from a hybrid state caused by the interaction of the Cs 6s level with the unoccupied dangling-bond state. This hybrid state has long been postulated in descriptions of the metal-semiconductor surface bond, and is responsible for the pinning of the Fermi level. The absence of dispersion in the state suggests that Cs/GaP(110) represents a realization of a Mott-Hubbard insulator, by comparison with results from other alkali-metal/compound-semiconductor systems

Electronic band structure of cubic CdSe determined by angle-resolved photoemission: Cd 4d and valence-level states

The valence-band structure of epitaxially grown cubic CdSe along the Γ−K−X direction is determined experimentally using angle-resolved photoelectron spectroscopy on the basis of the free-electron final band model. In the upper valence band the three main branches are determined from normal emission spectra over the range from 15 to 90 eV photon energy, and are found to conform with the general shape expected from this class of materials. The Cd 4d level exhibits considerable dispersion, which is reflected in the spectra. The experimental bands are compared with several calculations based on different schemes, and best agreement with respect to dispersion and binding energies is found for a calculation that takes into account electron self-interaction and relaxation

Enhanced surface metallic density of states in icosahedral quasicrystals

Valence and core-level photoemission spectra show that cleaved i-Al-Pd-Mn quasicrystals have a pronounced metallic signature. Spectra from states above EF, populated by increasing the sample temperature, indicate the presence of a shallow pseudogap 0.09 eV above EF. The Al 2p line asymmetry, on the other hand, which indicates metallic behavior, decreases with increasing photoelectron escape depth. This implies a decreasing density of states at EF with increasing distance from the surface, consistent with indications that the density of states near EF in the bulk is reduced. Our results thus help to resolve the apparent contradiction between the theoretical predictions for a bulk pseudogap, and the clear metallic Fermi edges in photoemission

Electronic structure of cubic gallium nitride films grown on GaAs

The composition, surface structure, and electronic structure of zinc blende–GaN films grown on GaAs (100) and (110) by plasma‐assisted molecular beam epitaxy were investigated by means of core and valence level photoemission. Angle‐resolved photoelectron spectra (photon energy 30–110 eV) exhibited emission from the Ga 3d and N 2s levels, as well as a clear peak structure in the valence band region. These peaks were found to shift with photon energy, indicative of direct transitions between occupied and unoccupied GaN bands. By using a free electron final band, we are able to derive the course of the bands along the Γ‐X and Γ‐K‐X directions of the Brillouin zone and to determine the energy of critical points at the X point. The relative energies of the Ga 3d and nitrogen 2s bands were also studied, and a small amount of dispersion was detected in the latter. The resulting band structure is discussed in relation to existing band structure calculations

Influence of the substrate lattice structure on the formation of Quantum Well States in thin In and Pb films on silicon

The substrate lattice structure may have a considerable influence on the formation of quantum well states in a metal overlayer material. Here we study three model systems using angle resolved photoemission and low energy electron diffraction: indium films on Si(111) and indium and lead on Si(100). Data are compared with theoretical predictions based on density functional theory. We find that the interaction between the substrate and the overlayer strongly influences the formation of quantum well states; indium layers only exhibit well defined quantum well states when the layer relaxes from an initial face-centered cubic to the bulk body-centered tetragonal lattice structure. For Pb layers on Si(100) a change in growth orientation inhibits the formations of quantum well states in films thicker than 2 ML.Comment: 16 pages, 7 figure

Tailoring the FeO/SiO2 ratio in electric arc furnace slags to minimize the leaching of vanadium and chromium

Based on recently published research on leaching control mechanisms in electric arc furnace (EAF) slags, it is assumed that a FeO/SiO2 ratio of around one leads to low leached V and Cr concentrations. This ratio influences the mineral phase composition of the slag toward higher amounts of spinel and a lower solubility of calcium silicate phases by suppressing the formation of magnesiowuestite and highly soluble calcium silicate phases. To evaluate this hypothesis, laboratory and scaled up tests in an EAF pilot plant were performed on slag samples characterized by elevated V and Cr leaching and a high FeO/SiO2 ratio. Prior to the melting experiments, the optimum FeO/SiO2 ratio was calculated via FactSageTM. In the melting experiments, the ratio was adjusted by adding quartz sand, which also decreased the basicity (CaO/SiO2) of the slag. As a reference, remelting experiments without quartz sand addition were conducted and additionally, the influence of the cooling rate of the slag was examined. The remelted (without quartz sand) and the remelted modified slags (with quartz sand) were analyzed chemically and mineralogically and the leaching behavior was investigated. The modification of the slags yielded a minimized release of V and Cr, supporting the hypothesis that the FeO/SiO2 ratio influences the mineralogy and the leaching behavior

Harding University Course Catalog 1988-1989

Catalog of Harding University 1988-1989https://scholarworks.harding.edu/catalogs/1050/thumbnail.jp