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The structural evolution during a sol to gel transition reaction in the K 2 O-Al 2 O 3 -SiO 2 system was investigated by using in situ small angle X-ray scattering (SAXS) technique. The results are interpreted as evidence of the presence of at least two different gel phases. The analysis shows that the primary phase is composed of small particles with characteristic size of???3.0 nm, and considerable size and shape variation. The primary phase is identified as a random phase in the Debye sense. The primary particles aggregate into larger formations with spherical symmetry. The size of larger aggregates (second phase) increases continuously in the course of gelation and levels off after reaching???15.0 nm. The volume fraction of the second phase keeps increasing until the end of the measurement which is far after the gelation (3-fold of the gelation time).

A sol to gel transition reaction of three metal alkoxides with water in the preparation of gel in the K2O---Al2O3---SiO2 system was investigated using in situ viscosity measurements and the Raman scattering technique. The viscosity measurements reveal that the viscosity of the solution and the dependence of the reduced viscosity on polymer concentrations change abruptly near the gelation point. The Raman scattering results suggested that the hydrolysis of the TMOS was the rate-limiting step of the overall reaction. It was also found that a basic solution with excess amounts of water was needed to synthesize a transparent crack-free gel.

Titania-supported molybdenum and cobalt-molybdenum catalysts were prepared by the dry impregnation and equilibrium adsorption techniques. Raman and Fourier Transform Infrared spectroscopy were used to follow the changes the catalysts underwent during the drying and calcination stages. The results indicate that the nature of the surface species depends on the loading, pH of the starting solution and the method of catalyst loading. It was found, for coverages calculated to be less than a monolayer, that the main surface species are tetrahedral molybdates. As the loading increases, octahedrally coordinated polymeric surface species form. Above the monolayer coverage, MoO3 is also formed. After calcination the spectra of catalysts prepared by the equilibrium adsorption technique change much less than those for catalysts prepared by the dry impregnation technique. Addition of cobalt to titania-supported molybdenum catalysts suppresses the formation of bulk MoO3 and leads to the formation of a cobalt molybdate phase. The results show that surface molybdates interact strongly with the support, TiO2.

The objectives of this project were the understanding of heteroepitaxial growth of SiGe/Si, dislocation control for highly mismatched layers, and the application of such heterostructures to high speed microelectronics and optoelectronics. A new technique of dislocation control, using a low-temperature Si buffer layer, has been identified. SiGe/Si heterostructure FETs have been fabricated, using this technique. Heterostructure bipolar transistors have been utilized to realize the first SiGe-based integrated photoreceivers. The electro-optic coefficients in SiGe/Si quantum wells have also been measured. Modulators, whose operation principle is based on the small conduction band offset, in this heterostructure, has been demonstrated theoretically and experimentally, for the first time. Theoretical work, involving a charge control study of the interfacial effects in p-MOSFETs.