Phase growth control in low temperature PLD Co: TiO2 films by pressure

This paper reports on the structural and optical properties of Co-doped TiO2 thin films grown onto (0001)Al2O3 substrates by non-reactive pulsed laser deposition (PLD) using argon as buffer gas. It is shown that by keeping constant the substrate temperature at as low as 310 °C and varying only the background gas pressure between 7 Pa and 70 Pa, it is possible to grow either epitaxial rutile or pure anatase thin films, as well as films with a mixture of both polymorphs. The optical band gaps of the films are red shifted in comparison with the values usually reported for undoped TiO2, which is consistent with n-type doping of the TiO2 matrix. Such band gap red shift brings the absorption edge of the Co-doped TiO2 films into the visible region, which might favour their photocatalytic activity. Furthermore, the band gap red shift depends on the films’ phase composition, increasing with the increase of the Urbach energy for increasing rutile content.

► Co-doped TiO2 thin films were grown onto c-cut sapphire by non-reactive pulsed laser deposition (PLD). ► Rutile and anatase phase tuning was achieved by varying only one experimental parameter: the background gas pressure, Pt. ► The growth temperature was set as low as 310 °C for both phases. ► Correlations of films’ band gap red shifts and Urbach energies with total pressure were established. ► Possible band gap tuning in the near-visible region.