Thickness dependence of the growth of magnetron-sputtered TiO2 films studied by Raman and optical transmittance spectroscopy

Thin sputtered films of TiO2 of various thicknesses are characterized by their strain along the crystalline c-axis. The Raman B-1g 519 cm(-1) mode experiences a strong blue shift, whereas the E-g 144 cm(-1) peak is at the standard position for all samples. The Raman intensity of the prominent E-g 144 cm(-1) peak increases upon annealing at 300 degrees C, contrary to the integral intensity of XRD reflexes which remains constant. The half-width of the E-g 144 cm(-1) peak is determined by the crystallite size. Dielectric modelling of the optical transmittance spectra indicates, for all samples, the existence of defect states leading to transitions 0.3-0.5 eV lower than the band gap. The growth process becomes stationary for a film thickness above 100 nm for rf-sputtered and above 200 nm for dc-sputtered films. (C) 2013 AIP Publishing LLC.