Description of TiO2 thin films treated in NH3 atmosphere by optical dispersion models

The influence of a reductive ammonia atmosphere on TiO2 sol-gel film structural and optical characteristics was investigated. X-ray Diffraction technique, X-ray photoelectron spectroscopy and Rutherford Back Scattering analysis were applied to study the crystallinity, oxidation state and element concentration profile of the modified films. Their optical properties were investigated by UV–Vis spectroscopy. The refractive index and extinction coefficient were obtained by fitting theoretical transmittance curves to experimental ones using Forouhi–Bloomer (FB) and Tauc–Lorentz (TL) physical models. Both models revealed slight decrease (up to 2.6–2.7 eV) of the FB and TL band gaps with increase of the treatment temperature. These results were discussed in terms of the additional energy levels creation due to the defect TiO2 structure formation during thermal treatment in reductive atmosphere.