Transparent Thin Films of Anatase Titania Nanoparticles with High Refractive Indices Prepared by Wet Coating Process

Abstract

We present a sol-gel derived anatase titania nanoparticle system which can be spin-coated to form thin films having high refractive index and excellent optical clarity. Stable titania suspensions were obtained through peptization of crude product in the presence of tetramethylammonium hydroxide. The particle sizes and morphologies were finely controlled by mild hydrothermal treatment at 200 degrees C. Three titania suspensions obtained by different hydrothermal reaction time showed stable suspensions without significant flocculation, and subsequently spin coated on the glass substrates. Without calcinations step, the resulting films exhibited fairly good optical clearance and refractive indices as high as 2.05. Narrow dispersity of the particle size and the stability of titania suspension also enabled the fabrication of inverse opal structure by templating method which could be further utilized as various applications such as photonic bandgap materials and photoelectrode for solar cells.