Tailoring crystalline structure of titanium oxide films for optical applications using non-biased filtered cathodic vacuum arc deposition at room temperature

Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the O₂ partial pressure (pO₂), is described in detail. The composition, morphological features, crystalline structure, and optical properties of the deposited films were systematically studied by Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Raman Spectroscopy, UV-vis spectroscopy, and spectroscopic ellipsometry. This systematic investigation allowed the identification of three different groups or growth regimes according to the stoichiometry and to the phase structure of the titanium oxide films. RBS analysis revealed that a wide range of TiO_x stoichiometries (0.6 < x < 2.2) were obtained, including oxygen-deficient, stoichiometric TiO₂ and oxygen-rich films. TiO, Ti₂O₃, rutile-type TiO₂, and amorphous TiO₂ phase structures could be achieved, as confirmed both by Raman and XRD. Therefore the results showed a highly versatile approach, in which different titanium oxide stoichiometries and crystalline phases especially suited for diverse optical applications can be obtained by changing only two process parameters, in a process at room temperature and without applied bias. Of particular interest are crystalline rutile films with high density to be used in ultra-high reflectance metal-dielectric multilayered mirrors, and reduced-TiO₂ rutile samples with absorption in the visible range as a very promising photocatalyst material.