Properties of TiO₂ thin films deposited by rf reactive magnetron sputtering on biased substrates

Highlights: • TiO₂ thin films were deposited on negatively biased substrates by rf magnetron sputtering technique. • The bias favors the formation of TiO₂ crystalline phase. • The roughness of the films increases and the grain size decreases as the bias voltage is varied between (0 and −100 V). • XPS reveals the presence of adsorbed humidity of the surface and Ti⁴⁺ oxidation state in the as prepared samples. - Abstract: TiO₂ thin films are of paramount importance due to their pervasive applications. In contrast to previous published works where the substrate was heated at high temperatures to obtain TiO₂ crystalline phase, we show in this study that it is possible to deposit crystalline TiO₂ thin films on biased and unbiased substrate at room temperature using reactive rf magnetron sputtering. The bias voltage was varied from 0 V to −100 V. The deposited films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy, Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and atomic force microscopy (AFM). The average crystallite size was estimated using x-ray diffraction. The results showed that the application of negative bias affects the surface roughness of the films and favors the formation of the rutile phase. The root mean square roughness (R_rms), the average grain size and the optical band gap of the films decreased as the substrate bias voltage was varied from 0 to −100 V. The UV–visible transmittance spectra showed that the films were transparent in the visible range and absorb strongly in the UV range. This study shows that biasing the substrate could be a promising and effective alternative to deposit TiO₂ crystallized thin films of engineered properties at room temperature.