The optical properties and band gap energy of nanocrystalline la Sr TiO thin films

The effects of microstructure on the optical properties of La Sr TiO thin films were investigated. Dense films with the thickness of ∼ 200 nm and grain size 14-30 nm were produced on monocrystalline sapphire substrates by using a polymeric precursor spin coating technique at annealing temperatures under 800°C. X-ray data showed the formation of a single-phase cubic perovskite-type structure similar to undoped SrTiO for annealing temperatures > 500°C. The results of optical measurements showed that the optical spectra varied with the change of the grain size. From these data, the absorption co-efficients were calculated and the band gap energy determined. In agreement with the quantum confinement model, it was shown that the band gap energy increased as the grain size decreased.