Raman spectral analysis of TiO2 thin films doped with rare-earth yttrium and lanthanum

Abstract

TiO2 thin films doped with rare-earth yttrium and lanthanum were prepared on quartz plate by sol-gel/spin-coating technique. The samples were annealed at 700 to 1100 ℃ and the Raman spectra of the samples were obtained. Analysis of Raman spectra shows that with increasing annealing temperature, the anatase form of undoped TiO2 thin film transforms eventually into the rutile phase with mixed anatase/ rutil phase as an intermediate. Yttrium doping and lanthanum doping of TiO2 thin films can inhibit the phase transformation, and the latter effect is stronger. Rare-earth doping refines grain size of TiO2 thin films and increases the internal stress, thereby preventing lattice vibration. The effect of La doping is stronger than yttrium doping. The samples show significant phonon confinement effect. That is to say, the characteristic Raman peaks blue shift and the full widths at half height increase and the peak shap easymmetricaly stretches with decrease of grain size.