Gradual and selective achievement of Rutile-TiO2 by thermal annealing amorphous TixOyNz films

To a large extent, future technological progress relies on the study−development of advanced materials with new and/or improved properties. The semiconductors titanium oxynitride (Ti _xO _yN _z) and titanium dioxide (TiO ₂) perfectly meet these requirements in the sense that their main chemical and structural properties can be customized, leading to successful contributions in optics, electronics, catalysis, bactericides surfaces, and photovoltaics applications, for instance. Motivated by these aspects, this paper reports on the structure and optical bandgap of Ti _xO _yN _z, as obtained by Raman scattering and optical transmittance spectroscopy, respectively. The study comprises a set of films produced by N ₂-plasma Ti sputtering and subsequently thermal annealed in an atmosphere of oxygen flux. As the thermal treatments advance, the Raman spectra indicate a gradual transformation of the films from amorphous+(nano/micro-)crystalline Ti _xO _yN _z to the crystalline Rutile phase of TiO ₂ (R-TiO ₂). Consistent with these structural changes, the optical bandgap of the films decreases from ∼ 3.2 to 2.5 eV, i.e., across part of the ultraviolet−blue spectral region. The analysis of the experimental data confirms the importance of nitrogen (in the early stages of sample preparation) on the achievement of R-TiO ₂ in a continuous and controllable way. Therefore, this paper shows the suitability of the Ti _xO _yN _z compound to produce films with well-defined crystalline TiO ₂-related structures and specific optical bandgap values.