The preparation and characterization of optical thin films produced by ion-assisted deposition

Abstract

Inert and reactive gas ion beams have been used in the preparation of high-quality optical thin films for use as dielectric coatings on optical components, solar selective absorbers, and protective films on Ag and Al mirrors. Films are deposited by electron-beam evaporation and simultaneous irradiation of the growing film at the substrate or by ion-beam sputtering with and without ion assistance. Substantial improvement in the film packing density has been achieved, the refractive indices increased, and water penetration through the films was suppressed. TiN has been deposited by Ti evaporation and nitrogen irradiation for use as an element in a high-temperature solar selective absorber. Amorphous hydrogenated silicon (a-Si:H) has also been produced by Si evaporation and hydrogen irradiation or by mixed ion-beam sputtering. Significant changes in the crystal structure of PbS have also been achieved by ion irradiation. Dielectric films of ZrO2, SiO2, and Al2O3 have been deposited by ion-assisted deposition and ZrO2 has been used as a highly successful protective coating on Al and Ag mirrors. The optical properties of the films have been studied and the film composition checked by x-ray diffraction, nuclear reaction analysis (NRA), Rutherford backscattering (RBS), x-ray photoelectron spectroscopy (XPS), and ion scattering spectroscopy (ISS).