Publications

In order to develop the next generation of high peak intensity lasers, new grating technology providing higher damage thresholds and large apertures is required. The current assumption is that this technical innovation will be multilayer dielectric gratings, wherein the uppermost layer of a thin film mirror is etched to create the desired binary phase grating. A variant of this is explored with the upper grating layer being a lower density gelatin-based volume phase grating in either sol-gel or dichromated gelatin. One key benefit is the elimination of the etching step.

Surfactant-templated silica thin films are potentially important materials for applications such as chemical sensing. However, a serious limitation for their use in aqueous environments is their poor hydrolytic stability. One convenient method of increasing the resistance of mesoporous silica to water degradation is addition of alumina, either doped into the pore walls during material synthesis or grafted onto the pore surface of preformed mesophases. Here, we compare these two routes to Al-modified mesoporous silica with respect to their effectiveness in decreasing the solubility of thin mesoporous silicate films. Direct synthesis of templated silica films prepared with Al/Si = 1:50 was found to limit film degradation, as measured by changes in film thickness, to less than 15% at near-neutral pH over a 1 week period. In addition to suppressing film dissolution, addition of Al can also cause structural changes in silica films templated with the nonionic surfactant Brij 56 (C{sub 16}H{sub 33}(OCH{sub 2}CH{sub 2}){sub n{approx}10}OH), including mesophase transformation, a decrease in accessible porosity, and an increase in structural disorder. The solubility behavior of films is also sensitive to their particular mesophase, with 3D phases (cubic, disordered) possessing less internal but more thickness stability than 2D phases (hexagonal), as determined with ellipsometric measurements. Finally, grafting of Al species onto the surface of surfactant-templated silica films also significantly increases aqueous stability, although to a lesser extent than the direct synthesis route.