X-ray absorption fine structure investigations on heat-treated Cr-doped titania thin films

Chromium-doped titanium oxide thin films were investigated in the as-deposited state and after thermal treatment (723 K for 3 h in air). X-ray diffraction data revealed an improvement in film crystallinity induced by the thermal treatment. Extended X-ray absorption fine structure data revealed similar atomic neighboring around Cr atoms in both as-deposited and annealed samples. A lattice contraction of ~ 2% is observed in the annealed samples. The 67% enhancement of the amplitude of the Cr 1 s X-ray absorption fine structure pre-edge peak after thermal treatment, which is a sign of “dipole-forbidden” 1 s → 3 d transitions, suggests strong alteration in the number of Cr 3 d vacancies, in spite of similar Cr local environment in the two kinds of investigated samples. We discuss here the Cr⁺ → Cr⁴⁺ and Cr²⁺ → Cr⁶⁺ changes induced by thermal treatment, and/or the evolution in local structures without inversion center.Refractive index dispersion spectra in the visible wavelength domain allowed us to compute the values of the dispersion energy, the single-oscillator energy and the coordination number of Ti atoms in both as-deposited and annealed samples.