Structural and optical properties of TiO2 thin films derived by sol-gel dip coating process

Nanocrystalline thin films of titanium dioxide have been fabricated on glass and silica substrates from partially hydrolyzed precursor solution. These films were subjected to heat treatment for 1 h at temperatures 100, 200, 300, 400, 500, 600, 700, 800 and 900 degrees C and characterized by XRD, SEM, XPS and optical techniques. As deposited films are found to be amorphous and also contain hydroxyl and organic functional groups. Films heat treated above 100 degrees C do not contain hydroxyl and organic functional groups. Microcrystalline behavior is observed in the films heat treated above 300 degrees C. Crystallite size increases from similar to 5 to 50 nm as sintering temperature is increased from 300 to 700 degrees C. Formation of anatase phase with c-axis length 7.03 angstrom is observed in the films annealed up to 700 degrees C. These films peel off from the substrate beyond 700 degrees C annealing temperature. Density as well as refractive index of the films increases with increase in annealing temperature up to 700 degrees C. Refractive index is found to show Cauchys behavior. Transmission better than 70% is observed in the visible range. There is a strong absorption around 370 urn, which is attributed to band gap absorption of the material. (C) 2007 Elsevier B.V. All rights reserved.