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Transition metal doped titania is nowadays a class of materials with promising photocatalytic and diluted magnetic semiconductor properties. Chromium-doped titanium oxide thin layers are deposited onto glass substrates by using dc reactive sputtering starting from three targets (two metallic titanium discs and one chromium disc), in (O2/Ar) mixture with partial pressure of oxygen of about one third of the total pressure of the gas mixture (0.35 Pa). The thickness of the thin films (in the range of 240 nm) was measured by using a profilometer and corroborated with cross-section SEM analysis. Samples were investigated as-deposited and following thermal treatment at (450 degrees/2 hours). Both as-deposited and annealed samples show amorphous structure, with no X-ray diffraction (XRD) pattern. X-ray absorption fine structure measurements are performed at the Doris storage ring facility in Hasylab, Germany, at both Cr and Ti K-edges. Extended X-ray absorption fine structure (EXAFS) revealed similar atomic neighbourhood around Cr in both as-deposited and annealed samples; however, with a lattice contraction of some 2 % in the annealed samples. Local atomic environment around Cr presents better defined coordination shells than the local atomic environment around Ti, where the Fourier transform of the EXAFS spectra evidenced ill-ordered neighbourhood, in agreeement with XRD. A new and interesting result is the strong enhancement (by a factor of two) of the amplitude of the pre- Cr K-edge peak after thermal treatment, which is a sign of "dipole-forbidden" 1s → 3d transitions. This suggests strong changes in the Cr number of 3d vacancies, although the local environment about Cr is similar in the two kinds of samples investigated. The discussed changes are Cr(3+) → Cr(6+) (as from Cr2O3 to CrO3) and Cr(2+) → Cr(4+) (as from CrO to CrO2) induced by thermal treatment, and/or evolution into local structures (distorted octahedral environments) without inversion center, where the amplitude of "dipole forbidden" transitions is known to increase. These observations could be exploited in order to achieve the desired ionization state (thus the Cr magnetic moment and the carrier density) in such materials. |