Substrate-dependent optical absorption characteristics of titanium dioxide thin films

We used the electron-beam evaporation method in various oxygen partial pressure environments to deposit TiO2 thin films on various glass substrates at 300 degrees C. We found the threshold oxygen partial pressures above which the film is transparent are different for films on various substrates. Below the threshold oxygen partial pressure, the refractive index and the extinction coefficient of the films varied from substrate to substrate. The films on substrates with higher threshold oxygen partial pressure were associated with a higher extinction coefficient and a higher growth rate. These phenomena are correlated with the appearance of rutile phase in the anatase phase, which is also correlated with variations in the Al2O3 and Na2O content in the substrates. The Al2O3 content in the substrate tends to enhance the formation of rutile phase in the film and to give a higher extinction coefficient for the film, while the Na2O content in the substrate tends to retard the rutile formation in the film and to give a lower extinction coefficient for the film. (C) 1997 Optical Society of America.