The effect of silver on the phase transition and microstructure of titanium oxide films grown by pulsed cathodic arc had been investigated by XRD, SEM and Raman spectroscopy. Following successive thermal annealing up to 1000 °C, microstructural analysis of annealed Ag-TiO2 films reveals that the incorporation of Ag nanoparticles strongly affects the transition temperature from the initial metastable amorphous phase to anatase and stable rutile phase. An increase of silver content into TiO2 matrix inhibits the amorphous to anatase phase transition, raising its temperature boundary and, simultaneously reduces the transition temperature to promote rutile structure at lower value of 600 °C. The results are interpreted in terms of the steric effects produced by agglomeration of Ag atoms into larger clusters following annealing which hinders diffusion of Ti and O ions for anatase formation and constrains the volume available for the anatase lattice, thus disrupting its structure to form rutile phase. The effect of silver on the optical and wetting properties of TiO2 was evaluated to demonstrate its improved photocatalytic performance.

Abstract--To test the hypothesis that berthierine in oolitic ironstones formed by diagenetic transformation of detrital kaolinite, laboratory experiments simulating the early diagenetic conditions were conducted. Representative sets of the initial sediment were prepared in distilled water and artificial seawater suspensions by mixing 4-13 g/liter kaolinite with Fe(OH)a precipitated from 0.1-0.3 M FeClz solutions. ~NazS204 was added to the suspensions as a reducing agent, and inert Nz atmospheres were used to maintain the required Eh between + 100 and -400 mV. The pH of the suspensions was controlled between 8 and 5 with dilute HC1. Within 300 days, the iron content of the bulk kaolinite in the seawater suspensions progressively increased from 0.18 to 2.44% at pH = 7 and Eh between -250 and -350 mV. Energy dispersive X-ray analyses of individual clay platelets in the final products showed progressive, temporal increase in Fe, and concomitant decrease in AI and Si. X-ray powder diffractometry revealed small d (001)-d(002) shifts, marked intensity reversals of (001) and (002) reflections, and the development of additional characteristic berthierine reflections with time. These data suggest progressive transformation of kaolinite to berthierine. Microprobe analyses of natural berthierine in oolitic ironstones also showed parallel patterns, which substantiate such progressive transformation from the margin toward the core of the ooids. The transformation did not take place in distilled water. The addition of Mg 2 § to the distilled water suspensions, however, promoted the transformation.

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Selective postgrowth control of the photoluminescence ͑PL͒ wavelength has been demonstrated for a single layer self-organized In 0.5 Ga 0.5 As/GaAs quantum dot ͑QD͒ structure. This was achieved by rapid thermal processing of dots using different dielectric caps. Selective band gap shifts of over 100 meV were obtained between samples capped with sputtered and plasma enhanced silica deposition, with the band gap shift under regions covered with plasma enhanced chemical vapor deposition SiO 2 less than 70 meV. The effects of different caps on the PL linewidth were also observed. The differential band gap shift will enable the integration of passive and active devices in QD systems.

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