In this paper experiments with reactive evaporation of the starting materials Ti, TiO, Ti2O3, Ti3O5, and TiO2 to obtain nonabsorbing TiO2 films are under discussion. For the starting materials TiO and Ti3O5 the dependence of the TiO2 film refractive index on the substrate temperature, oxygen pressure, and deposition rate was measured. For TiO dispersion curves of the resulting TiO2 films as a function of the substrate temperature during film formation were determined. The successive evaporation of the different starting materials resulted in the formation of λ/4 TiO2 films with different refractive indices. This phenomenon was most obvious during the first evaporation. It disappeared after several evaporations in two groups of TiO2 films with different refractive indices. From the beginning only the starting materials Ti and Ti3O5 resulted in TiO2 films with constant refractive indices. The first material produced a high, the latter a lower film index. Depending on the number of evaporations performed, both types of TiO2 films can be obtained with TiO. The films and residues in the crucibles were also subjected to chemical analyses. An attempt was made to explain the optical properties of the resulting TiO2 films with regard to crystal structure, chemical composition, packing density influenced by the molecular composition of the vapor beam, chemical reaction with the crucible, substrate temperature, O2 pressure, and deposition rate.
H. K. Pulker, G. Paesold, and E. Ritter, "Refractive indices of TiO2 films produced by reactive evaporation of various titanium-oxygen phases," Appl. Opt. 15, 2986-2991 (1976)