Growth and crystallization of Cobalt-doped TiO2 alloys: Effect of substrate and annealing temperature

Abstract

This work presents a study of the structural and optical properties of cobalt-doped titanium dioxide thin films prepared via the DC Magnetron Co-Sputtering technique using TiO2 and Co targets with 99.99% purity; these thin films were deposited on three different substrates: Soda-lime glass, titanium foil and silicon wafer. The resulting films deposited on glass were then submitted to annealing processes at temperatures ranging from 500 °C to 600 °C. X-ray diffraction measurements revealed limited crystallization of the as-deposited samples, whilst the annealed samples showed several crystalline phases, including cobalt oxide (Co3O4) and a ternary phase (CoTi2O5); SEM studies helped to corroborate that the inclusion of TiO2 into the thin film decreases its crystallinity, obtaining nanostructures smaller in size as compared with samples containing cobalt. UV-vis-NIR measurements revealed an increase in transparence of the thin films after annealing at 600 °C, evidencing extrinsic absorption phenomena, consistent with the formation of binary phases inside the semiconductor matrix. From XPS measurements, the oxidation states for Co and Ti were obtained.