Correlations between the Optical Properties and the Microstructure of TiO_2 Thin Films Prepared by Reactive Electron-beam Evaporation

摘要

High refractive index TiO_2 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 120 deg C to 300 deg C. 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 120 deg C to 300 deg C, 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 TiO_2 thin films deposited on BK7 glass at substrate temperatures of 120 deg C, 200 deg C and 300 deg C is amorphous, after post-annealing under air condition at 400 deg C for 1 hour, the amorphous structure is crystallized, the crystal phase is of 100 percent anatase with strong preferred orientation (004) and the grain size of crystalline is within 3.6-8.1 nm, which is consistent with results from SEM observation.