TiO2 coatings obtained by reactive sputtering at room temperature: Physical properties as a function of the sputtering pressure and film thickness

TiO2 layers with crystalline anatase structure have been attained on unheated glass substrates, by reactive sputtering from a metallic target, using the sputtering pressure to change the energy of the particles arriving to the film surface. Such energy and the time of plasma exposure also influence the morphology and other physical properties of the sputtered films. The deposition time has been ranged to obtain TiO2 coatings with different thicknesses from 0.24 to 1.08 μm and at various total pressures from 0.2 to 1.0 Pa. Overall characterization of the samples has been performed by X-ray diffraction, atomic force microscopy and spectrophotometry. The effects of the sputtering pressure and the film thickness on the crystalline structure (interplanar distance and mean crystallite size), the morphology (roughness and surface area) as well as the optical properties (refractive index, extinction coefficient) have been established. A direct relation between optical and morphological characteristics, and the calculated film porosity has been proven. Such porosity is well controlled by the deposition parameters; these allow tuning the optical and morphological properties of the sputtered TiO2 coatings as required for different applications.