Structural investigations of SiO-CeO₂ thin films

Abstract

Aspects of the structure of vacuum co-evaporated SiO-CeO₂ thin films are elucidated by first presenting the optical transmission edges for a series of such films. These show a differentiation into two distinct groups, and the presence of weak absorption minima, possibly defect-induced, confined to one of these groups. Previously obtained infrared (IR) results are compared with these UV results, and the IR evidence for the O ^sup0_inf1 and O ^sup1_inf3 defect centres associated with oxygen sites is noted. The electron spin resonance (ESR) results for pure a-SiO thin films are then discussed in terms of those of vitreous SiO₂, and it is concluded that only O ^sup0_inf1 and O ^sup+_inf3 ESR-related defect centres exist in amorphous SiO films in significant quantities. It is also concluded that adding CeO₂ to the films reduces the O ^sup0_inf1 concentrations via chemical bonding, while the O ^sup+_inf3 03 centres remain unaffected. Finally it is shown that the separate identity of any possible defect-induced optical absorption bands in the series from those expected for a-SiO and CeO₂ can be used as new evidence for the presence of Si-Ce bonding.