Mesoporous SiO2 thin films containing photoluminescent ZnO nanoparticles and simultaneous SAXS/WAXS/ellipsometry experiments

Abstract

We report the formation of ZnO/SiO2 nanocomposite thin films. They are composed of 5 nm sized-wurtzite ZnO nanoparticles nucleated within vitreous SiO2 which was in the form of either an ordered mesoporous or a dense matrix. Mesoporous thin films were obtained by evaporation induced self-assembly from the chemical solution deposition of solutions containing TEOS, ZnCl2, and Pluronic-type block copolymers as structuring agent. Direct thermal treatment in air was applied to achieve the desired film characteristics. Dense or highly ordered mesoporous (pore size = 6 nm and pore volume = 60%) films can be achieved with high optical quality. When 50 mol% ZnO is used, the mesoporous films exhibit a very low refractive index of 1.17, which suggests a high accessible porosity that is ideal for molecular diffusion towards ZnO nanoparticles. In these films, the similar intensity of the UV and visible emission bands reveals a high amount of oxygen defects, making them well suited for applications in stimulated emitters, actuators, lasing cavities, or optical sensors. The present results are supported by in situ time-resolved grazing incident small angle X-ray scattering/wide angle X-ray scattering/thermal ellipsometry analysis experiments, which allow for the study of the crystallization kinetics of ZnO within amorphous matrices. The present work constitutes an example of a one-pot synthesis of divalent oxide nanoparticles dispersed in mesoporous silica that can virtually be extended to most divalent metal oxides, but also to other processing such as aerosol pulverisation of powders.