Abstract:The Raman spectroscopy method was used for structural characterization of TiO 2 thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125-425 • C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 • C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 • C and retained this phase even after annealing at 900 • C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 • C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.

Transmission spectra of TiO2 films grown by atomic layer deposition on fused silica have been analysed by using Lorentz dispersion and a model consisting of two sublayers inside a film. It has been shown that the deposition process parameters significantly influenced the refractive index gradient in the film growth direction. The films grown at a lower flow of the carrier gas showed a 35 nm thick sublayer with low refractive index at the silica substrate and a layer with a higher refractive index at the film surface. The films deposited at higher carrier gas flow had a higher refractive index at the substrate and a lower refractive index at the film surface. The results also demonstrate that by using a parameter modelling one can obtain some information about the internal structure of a film even if there are no clearly defined interference fringes in a transmission spectrum.