Self-assembled mesoporous silica-germania films

Silica-germania thin films are important materials for photonic applications, but synthesis of these films is quite difficult to achieve especially with the task of obtaining a homogeneous structure. We have prepared mesoporous silica-germania films via evaporation-induced self-assembly from ethanolic solutions of Si and Ge chlorides, using a triblock copolymer as the templating agent. The mesostructure has been found to have tetragonal symmetry, and the degree of order decreased with increasing Ge content. X-ray photoelectron spectroscopy has shown that the chemical composition of the films is close to the nominal composition. Infrared analysis has revealed that the pore walls are highly condensed and residual hydroxyls are present as isolated. or hydrogen bonded silanols in short chains. UV-vis absorption and photoluminescence spectra have been correlated with the presence of photoactive oxygen-deficient Ge2+ centers which can give rise to a variation in the refractive index upon high-power density UV irradiation.