Sol-Gel Synthesis of Thick Ta_2O_5 Films for Photonic Band Gap Materials

摘要

PVP has been shown to be an effective binder material in the sol gel synthesis of thick, crack free Ta_2O_5 films for high temperature applications. This study was undertaken to investigate the effect of PVP interaction with the solvent and metal complex in the sol precursor via NMR, FTIR, TGA, XPS, SEM, and XRD analytical tools. It has been reported that the type of Ta_2O_5 films obtained from sols of different ages vary in thickness and microstructure, suggesting that there was a progressive change occurring in the composition of the sol precursor with time. This is due to different particle growth rates around metallic centers during Ta—O—Ta network formation resulting in spherical particles. This type of microstructure hydrogen bonds with the PVP matrix in a manner that effectively relieves stresses that occur in the film during solvent removal and calcination processes. The resulting films are found to be stable and crack free with maximum thickness of films deposited from freshly prepared sols. With time, there is continued polycondensation of the Ta—O—Ta network yielding denser, thinner films with particles of larger diameter.