High-refractive-index thin films prepared from aminoalkoxysilane-capped pyromellitic dianhydride-titania hybrid materials

High-refractive-index aminoalkoxysilane-capped pyromellitic dianhydride (PMDA)-titania hybrid optical thin films (TP0-TP8) were synthesized and characterized in this study. They were prepared with PMDA, aminopropyltrimethoxysilane, and titanium(IV) isopropoxide via a sol-gel process followed by spin coating and multistep baking. Through adjustments in the concentration and reaction time, the inorganic content in the hybrid thin films could be as high as 59.1 wt %. The Fourier transform infrared results indicated successful bonding between the organic and inorganic moieties. However, residues of the chelating ligands were found in the hybrids with high titania contents, affecting their thermal and optical properties. Field emission scanning electron microscopy results suggested a nanosized domain of the titania segment in the hybrid materials TP0-TP8. An atomic force microscopy study suggested that the hybrid thin films had good planarization. The dispersions of the refractive index and extinction coefficient in the wavelength range 190-900 nm were studied. The refractive indices of the prepared hybrid thin films at 633 run increased linearly from 1.567 to 1.780 with increasing titania content. However, the Abbe numbers of the hybrid thin films showed an opposite trend. Excellent optical transparence was obtained in the visible region for the prepared hybrid thin films. (C) 2001 John Wiley & Sons, Inc.