Correlations between the optical properties and the microstructure of TiO2 thin films prepared by reactive electron-beam evaporation

High refractive index TiO2 thin films were deposited on BK7 glass by reactive electron - beam (REB) evaporation at pressure of 2 x 10(-2) Pa, deposition rate of 0.2 nm/s and at various substrate temperatures from 120degreesC to 300degreesC. The refractive index and the thickness of the films were measured by visible spectroscopic ellipsometry (SE) and determined from transmission spectra. Optical properties and structure features were characterized by UV-VIS, SEM and XRD, respectively. The measurement and analysis on transmission spectra of all samples show that with the substrate temperature increasing from 120degreesC to 300degreesC, the refractive indices of thin films increase from 1.7 to 2.1 and the films after heat treatment have higher refractive indices due to its crystallizing. The XRD analysis results indicate that the structure of TiO2 thin films deposited on BK7 glass at substrate temperatures of 120degreesC, 200degreesC and 300degreesC is amorphous, after post-annealing under air condition at 400degreesC for 1 hour, the amorphous structure is crytallized, the crystal phase is of 100% anatase with strong preferred orientation (004) and the grain size of crystalline is within 3.6-8.1 nm, which is consisient with results from SEM observation.