Changes of Thickness and Optical Constants of Boron Oxide Thin Films During Heating in Air

Changes of the thickness and optical constants of boron oxide films deposited on substrates of sapphire glass, sitall, and polycrystalline massive aluminum were studied directly during heating in air in the temperature range 24–700oC using single-wave and spectral ellipsometry methods. The high hygroscopicity of these films was demonstrated and decreased after their preliminary annealing. It was shown that the film thickness continuously decreased in the studied temperature range due to dehydration processes in the temperature range up to 300°C. The decrease in the film thickness at higher temperatures was explained by slow evaporation of boric acid formed in the film. It was shown that the deposition of a boron oxide film on the aluminum surface did not affect its oxidation rate.