High Refractive Index Silica-Titania Films Fabricated via the Sol–Gel Method and Dip-Coating Technique—Physical and Chemical Characterization

Crack-free binary SiO(x):TiO(y) composite films with the refractive index of ~1.94 at wavelength 632.8 nm were fabricated on soda-lime glass substrates, using the sol–gel method and dip-coating technique. With the use of transmission spectrophotometry and Tauc method, the energy of the optical band gap of 3.6 eV and 4.0 eV were determined for indirect and direct optical allowed transitions, respectively. Using the reflectance spectrophotometry method, optical homogeneity of SiO(x):TiO(y) composite films was confirmed. The complex refractive index determined by spectroscopic ellipsometry confirmed good transmission properties of the developed SiO(x):TiO(y) films in the Vis-NIR spectral range. The surface morphology of the SiO(x):TiO(y) films by atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods demonstrated their high smoothness, with the root mean square roughness at the level of ~0.15 nm. Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy were used to investigate the chemical properties of the SiO(x):TiO(y) material. The developed binary composite films SiO(x):TiO(y) demonstrate good waveguide properties, for which optical losses of 1.1 dB/cm and 2.7 dB/cm were determined, for fundamental TM(0) and TE(0) modes, respectively.