Optical dispersion in spun nanocrystalline titania thin films

Sol-gel derived titanium dioxide (TiO2) films are prepared on silicon substrates using the method of spin-coating with different speeds from 1000 to 6000 rpm. Spectroscopic ellipsometric measurements provide dispersion of the refractive index and extinction coefficient within the wavelength range of 300-1000 nm. The behaviour is in agreement with the single oscillator model. Optical absorption is believed to be due to allowed indirect transition over the optical gap of approximately 3.2 eV.