RAMAN-SPECTROSCOPY OF THERMALLY ANNEALED TIO2 THIN-FILMS OBTAINED BY CHEMICAL VAPOR-DEPOSITION AND THE SPRAY METHOD

Thin polycrystalline films of TiO2 deposited by chemical vapour deposition (CVD) and the spray method have been examined by Raman spectroscopy before and after thermal annealing at 100, 200, 300, 500, 800 and 900-degrees-C in a non-oxidizing atmosphere of H-2. According to Parker and Siegel [J Mater Res, 5, 1246 (1990)] it is possible to calibrate a Raman spectrum to the oxygen non-stoichiometry of TiO2. Curves are used as calibrational ones for the peaks of '144 cm-1' anatase vibrational mode and '443 cm-1' vibrational rutile mode. It can be seen that for CVD samples obtained non-stoichiometry reaches a maximum at 500-degrees-C and goes back to stoichiometry at the phase transition temperatures in the range of 800-900-degrees-C. For the samples obtained by the spray method non-stoichiometry reaches a maximum at the lower temperature of 200-degrees-C. In the whole range from room temperature to 900-degrees-C the spray method obtained samples are much more non-stoichiometric than CVD obtained samples. Furthermore, Raman spectra of CVD obtained TiO2 films annealed at 900-degrees-C in hydrogen reveal an amorphous phase immediately before the anatase-rutile phase transition. For samples obtained by the spray method we did not observe the same phenomenon.