Nucleation of titania nanocrystals in silica titania waveguides

SiO2(1−x)-TiO2(x) monomode waveguides at 632.8 nm, with x in the range 0.07–0.2 and thickness of about 0.4 μm, were deposited on silica substrates by a dip-coating technique. Nucleation of TiO2 nanocrystals and the growth of their size by thermal annealing up to 1300◦C were studied by waveguided Raman scattering in the SiO2(0.8)-TiO2(0.2) composition. In the low frequency region (5–50 cm−1) of the VV and HV polarized Raman spectra the symmetric and quadrupolar acoustic vibrations are observed. The mean size of the titania particles are obtained from the frequencies of the Raman peaks. The results are compared with those obtained from the measure of the linewidths in the X-ray diffraction spectra. Nanocrystals with a mean size in the range 4–20 nm are obtained by thermal annealing in a corresponding range of 700–1300◦C.