Refractive index of thin films of SiO_2, ZrO_2, and HfO_2 as a function of the films’ mass density

Abstract

Series of amorphous SiO2, ZrO2 and HfO2 films were prepared by electron-beam evaporation at various oxygen pressures such that the packing density varied from 0.6 to 0.82. Transmittance spectra were evaluated with respect to thickness and refractive index by application of analytical formulas to the interference extrema and by dielectric modeling. The thickness of the films ranged from 150 to 1500 nm. The coefficients of Cauchy and Sellmeier dispersion curves were determined as a function of the packing density. The mass density of the compact amorphous grains was estimated by an effective-medium theory and a general refractivity formula. It is similar to those of the crystalline materials. We used the optical data to design multilayer coatings for laser applications in a broad spectral range, including the UV.