Influence of post-deposition annealing on the properties of nanostructured TiO2 thin films grown by RF magnetron sputtering for photonic applications

In this work, nanostructured TiO2 thin films were successfully grown on glass substrates at room temperature by using a RF magnetron sputtering technique. The effect of the post-annealing treatment for one hour at 400–600... [ view full abstract ]

In this work, nanostructured TiO2 thin films were successfully grown on glass substrates at room temperature by using a RF magnetron sputtering technique. The effect of the post-annealing treatment for one hour at 400–600 °C on the structural, morphological, optical and waveguide properties were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-Visible spectrophotometry and m-lines spectroscopy (MLS). The results show that all prepared films exhibit (101) XRD peak corresponding to the anatase phase of TiO2 and those annealed revealed an improvement in crystallinity. The latter being consistent with the clear Raman peaks observed around 144, 197, 399, 515, 519 and 639 cm−1, attributed to the Raman active modes of anatase phase with symmetries Eg, Eg , B1g , A1g, B1g and Eg , respectively. SEM micrographs and AFM images showed that as-grown TiO2 film displayed a homogeneous and smooth surface consisting of small grain size particles, while increasing the annealing temperature resulted in larger grain size and rougher surfaces. The UV-Visible transmittance results show that as-grown films were transparent with an average transmittance of more than 75 % in the visible region. Whereas a slight decrease in the transmission and a blue shift of the absorption edge from 3.50 to 3.56 eV were observed with annealing temperature. MLS measurements at 633 nm wavelength put into evidence that all TiO2 planar waveguides demonstrated a well-guided single mode for both transverse electric (TE) and transverse magnetic (TM) polarized light and their refractive indexes were found to increase with annealing temperature. Moreover, the ordinary and extraordinary refractive index and the birefringence values of the TiO2 thin film annealed at 600 °C were very close to the corresponding single-crystal anatase values indicating its higher degree of crystallinity.