Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvi, 205 p.; also includes graphics (some col.). Includes bibliographical references (p. 196-205).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 103-106). Also available on the World Wide Web.

The nature of diffusion along thin evaporated films has been studied by optical and transmission electron microscopy. The thicknesses of the films were measured by multiple-beam interferometry. A preliminary survey of some 22 binary metal systems showed that only four - Ag-Se, Cu-Se, Cu-Te, and Ag-Te - diffused measurably at room temperature. In these four systems it was found possible to study only the diffusion of Cu or Ag into Se and Te; the reverse diffusion experiments failed, presumably because of extensive Kirkendall porosity which developed on the Se or Te side of the diffusion couples, impeding the motion of these atoms. The room temperature growth rates in each system were observed to be higher when the structure of the Se or Te consisted of isolated islands with a highly disordered inter-island network. This effect was attributed to a short circuit diffusion process analogous to grain boundary diffusion which took place in the inter-island channels. The effect was more pronounced in Cu-Te and Ag-Te where electron microscopy observations of the phase boundary interfaces showed a marked tendency for grain boundary diffusion to occur at all Se and Te thicknesses. For continuous films of Se and Te, the growth rates were found to be independent of the absolute thickness. Because of the evaporation geometry used in depositing the couples, there was a critical thickness ratio of Ag or Cu to Se or Te that had to be exceeded in order for diffusion to proceed. Theoretical treatment of the problem, based on the stoichiometry of the phases formed during diffusion, gave predictions of the critical ratio that were generally in good agreement with the experimental values obtained. In each system the critical ratio was found to be independent of the absolute Se or Te thickness. It was also possible to predict the composition of the phase formed during diffusion using the critical ratio. In every system but Cu-Te, the composition determined in this way was in agreement with that given by electron diffraction analysis of the diffusion zone. The activation energies for diffusion in Ag-Se, Cu-Te, and Ag-Te were fairly low suggesting that short circuit diffusion was the predominant mechanism in these systems. The activation energy in Cu-Se was quite large (23 kcal/mole), and it appears that the diffusion mechanism in this case is not consistent with that in the other systems. An interesting observation made during electron microscopy studies in Cu-Se was the formation of a second phase when high electron beam intensities were used. This phase (Cu₃Se₂), not observed in normal diffusion experiments up to 5 0°C, grew dendritically in the presence of the electron beam. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The work contained in this thesis is concerned with the elucidation of the growth mechanism responsible for the formation of silicon dioxide by plasma anodization. Three possible theories for the growth mechanism have been considered; namely, (1) the rate-limiting diffusion theory (2) the classical theory of high-field ionic conduction and (3) the impact ionization theory. The verification of the applicability of any of the above three theories required the design and construction of (a) an in situ film thickness measuring system and (b) a plasma anodization system capable of controlling the substrate temperature. The experimental data could not be accounted for by either the rate-limiting diffusion or high-field ionic conduction theories, but good agreement was found with predicted results from an impact ionization theory. The development of a suitable impact ionization theory yielded a value for the electron mobility in SiO₂ which was almost identical to the average value calculated from recent Hall effect measurements. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis reports the first detailed study of the stoichiometry control mechanisms and physical properties of ZnO films deposited by dc planar magnetron sputtering of a Zn target in a reactive Ar/0₂ atmosphere. Control of film stoichiometry was achieved using a subsidiary rf discharge at the substrate and a reactive gas baffle surrounding the target. The reactive gas baffle was shown to enhance film oxidation by decreasing the metal flux to the substrate and increasing the oxygen partial pressure near the substrate. Rutherford backscattering analysis of film stoichiometry demonstrated that the effect of the rf discharge was to increase the O/Zn composition ratio. This oxidation was shown to occur through preferential resputtering and preferential evaporation of excess Zn and by activation and ion plating of oxygen species. Resputtering and evaporation rates were found to be enhanced above that expected for bulk Zn, due to the weak bonding of surface adatoms during film growth. Conducting ZnO films produced at various values of the rf-induced substrate bias voltage were characterized for electrical, optical and structural properties using Hall probe,. X-ray diffraction, electron microscope, and visible and infrared spectroscopy techniques. Films deposited at low substrate bias (0 to -50V) were found to have a large Zn excess (15%) resulting in low electron mobilities (1 cm²/Vs), high resistivities (10⁻² Ωcm) and were strongly absorbing in the visible. Films deposited at high substrate bias were nearly stoichiometric, optically transparent and had high electron mobilities (15 cm²/Vs) resulting in low resistivity (10⁻³ Ωcm). The optical properties of transparent conducting films for wavelengths 0.4 to 20 /im were modelled by the Drude theory of free electrons using measured electrical transport properties. The original goal of this work, to develop a heat mirror coating suitable for manufacture, was achieved by bias sputter deposition of ZnO onto uncooled polyester sheet at deposition rates approaching 75 nm/min. The best heat mirror films had a transmission to solar energy of 75% and an 85% reflection of 300 K blackbody radiation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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No description available.

Master of Science

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Various metal phthalocyanines have been used as dyes, catalysts, indicators, electrophotographic receptors and more recently as active elements in chemical sensors and photoconductive materials for solar energy conversion applications. Of the MPc's, VOPc, GaPc-Cl and TiOPc have shown promise for solar energy conversion devices. GaPc-Cl has also shown promise as a chemical sensor. Up to this point in time, the focus of Pc research in this group has been in the direction of characterizing the photoelectrochemical properties of these materials. Recently, solid state studies of TiOPc have been done to determine the electronic properties of a tetravalent metal Pc, such as conductivity and photoconductivity. Such solid state measurements are facilitated by the use of interdigitated microelectrode arrays which are coated with thin films of various Pc's.