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Photoemission study of solid surfaces and interfaces
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|Title:||Photoemission study of solid surfaces and interfaces|
Solids -- Spectra
|Abstract:||This PhD dissertation is concerned with an experimental study of solid surfaces and interfaces. The electronic structure of magnesium hydride, chemisorption of oxygen or hydrogen on the Kg surface, and photoeffect of the Pd/SiOx/Si interface were investigated using the techniques of ultraviolet photoemission (UPS), x-ray photoemission (XPS), and interfacial photoemission (photoemission into solution). The core level binding energies, the valence bandwidth and the volume plasmon energy of KgH2 were determined from the x-ray photoelectron spectra. The observed plasmon energy was found to be useful in calculating the average energy gap and the static dielectric constant of MgH2, which is new information on MgH2. Measurements of uv photoemission from the Mg surface were made at photon energies a few eV above the photoelectric threshold before and after exposure to oxygen or hydrogen. The oxygen induced vacant-state features in the photoelectron spectra appear to be in good agreement with the calculated resonant state energy levels, suggesting that both singly anionic Oˉ complex and doubly charged O^2- complex exist at the initial stage of oxidation of the Kg surface. This is a new technique for observing the initial stage of chemisorption on Mg. The uv photoelectron spectra and spectral photoelectric yield also provided evidence of coadsorption of hydrogen and oxygen as magnesium hydride-hydroxide. From the XPS study of the Pd/SiOx/Si interface under the visible light bias, we developed a novel method of making non-destructive testing of the open-circuit photovoltage at the interface. The core level spectra of Pd 3d5/2 was observed to shift to higher (lower) binding energy for the n-type (p-type) Si substrate under illumination, in agreement with the Schottky photovoltaic theory. This shift was found to be sensitive to the presence of oxygen or hydrogen which can change the Schottky barrier height. This technique appears to be a promising method of investigating the effect of metal microclusters on the semiconductor surface electronic properties. The effect of hydrogen on the photoresponse of the Pd/SiOx/Si photoelectrode was also investigated using the solid/electrolyte interfacial photoemission technique. Hydrogen was used to exploit the fact that exposure to hydrogen can lower the work function of Pd. The results obtained at low light intensity (6.4 microwatts/cm2) agree with the metal/semiconductor interface model. However, at high light intensity (34 milliwatts/cm^2), our results of p-type Si/SiOx/Pd support the metal/solution interface model. The dependence of the photocurrent change on light intensity suggests that the magnitude of the surface recombination rate constant is important in locating the rate-determining step in the photoelectrochemical system. The results help resolve the controversy over the proposed models.|
Thesis (Ph. D.)--University of Hawaii at Manoa, 1990.
Includes bibliographical references (leaves 118-122)
xv, 122 leaves, bound ill. 29 cm
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|Appears in Collections:||Ph.D. - Physics|
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