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A low-temperature method, supercritical CO2 fluid (SCCF) technology, was applied for oxidation of metal Zn film on glass substrate at 60¢XC. In this study, Zn film was deposited by DC sputtering at room temperature and post-treated by SCCF, which is mixed with 0.15 vol % H2O. The scanning electron microscopy (SEM) images and transmission electron microscopic (TEM) indicate that high density ZnO Nanotubes were formed on the glass substrate. SCCF technology has shown successful oxidation the Zinc at low temperature for the first time.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 106-113). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 106-113). Also available on the Internet.

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Great interest has been directed toward the study of polymer thin films recently due to their emerging applications, and appreciable deviated properties and phenomena as compared with bulk polymers. Carbon dioxide (CO₂) has received attention as an environmentally benign alternative to hazardous industrial solvents. Unlike conventional liquid solvents, the density and hence the solvent strength of supercritical CO₂ can be tuned by small variations in pressure, temperature or both. The objective of this work is to study the interaction between high pressure CO₂ and polymer systems. We introduced the methodology used in this dissertation. The combination of gradient theory of inhomogeneous systems and Sanchez-Lacombe Equation of State is used to calculate the interfacial properties, such as interfacial density profile, interfacial tension and interfacial thickness. We first investigated the adsorption of supercritical fluid on polymer surfaces. We showed analytically that surface adsorption of high pressure fluid on an attractive surface is proportional to the compressibility of the fluid. We have also investigated numerically the sorption of supercritical CO₂ on poly(dimethylsiloxane) (PDMS) and polyisobutylene (PIB), and supercritical 1,1-difluorethane on PS. By calculating the Gibbs adsorption and adsorption layer thickness of the supercritical fluids, we found in all cases that maximum adsorption occurred when the supercritical fluid was near its compressibility maximum. We then examined the compatibilization effect of supercritical fluid on two incompatible polymers. We calculated the interfacial density profile, interfacial thickness and interfacial tension between the two polymers with and without the supercritical fluid. We found that the interfacial tension was decreased and the interfacial thickness was increased with high pressure super-critical fluid for the ternary systems we have investigated. No enhancement or deleterious effects on compatibilization were observed as the critical point was approached and the compressibility became large. We also examined the morphological structures of asymmetric poly(ethylene oxide)-b-poly(1,1'-dihydroperflurooctyl methacrylate) (PEO-b-PFOMA) thin films upon annealing in supercritical CO₂. The strong affinity between PFOMA and CO₂ was found to induce phase segregation when annealing PEO-b-PFOMA films as compared with vacuum at the same temperature.

Supercritical CO₂ (scCO₂) is emerging as a viable and environmentally sustainable platform for nanomaterials synthesis due to its tunable solvent properties combined with low surface tension and viscosity, which allow rapid, non-destructive wetting within small features. However, to advance the utility of this fluid, a more thorough understanding of surface chemistry at high pressures is needed. In this study, the behavior of reactive solids in scCO₂ was examined by etching thin dielectric, metal, and alloy films to determine the fundamental mechanisms controlling the reactions. Models were developed to describe the etching processes and to benchmark scCO₂ with conventional methods. Dielectric SiOₓNy films were etched with an HF/pyridine complex dissolved in scCO₂. The anhydrous etching process resulted in formation of a residual (NH₄) ₂SiF₆ layer that limited transport of reactants to the film and caused a drop in reaction order. Partial removal of the salt was accomplished by sublimation under vacuum. Etching of thin CuO films with hexafluoroacetylacetone (hfacH) in scCO₂ was studied and found to occur via a 3-step Langmuir-Hinshelwood reaction sequence. The kinetic model showed that lower scCO₂ densities favored hfacH adsorption on the CuO surface and that scCO₂ solvation forces lowered the activation barrier for the rate-limiting step. Adding up to 10× the molar ratio of pure H₂O to hfacH nearly doubled the etching rate through formation of a hydrogen-bonded hfacH complex. Both bulk and thin film AgCu alloys were selectively etched in scCO₂ to generate nanoporous Ag structures. As Cu was preferentially removed through selective oxidation and chelation, the Ag atoms conglomerated into successively larger clusters similar to mechanisms reported in aqueous phase dealloying. Supercritical dealloying was observed at Cu compositions below typical parting limits, suggesting enhanced fluid transport in the evolving pores. When using in situ oxidation, the etching reaction was limited by decomposition of H₂O₂. Inverse space image analysis of samples with initial phase domain sizes between 250 - 1000 nm showed that below a threshold of approximately 500 nm, the dealloyed feature size mimicked the starting microstructure. Larger phase domains prohibited surface diffusion of Ag between phases producing a mixture of large and small Ag nanostructures.

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