Effects of oxygen-to-argon ratio on crystalline structure and properties of Y2O3 anti-reflection films for freestanding CVD diamond

Abstract

Y2O3 anti-reflection films were deposited on freestanding chemical vapor deposited (CVD) diamond substrates by radio frequency magnetron sputtering. The effects of oxygen–argon ratio on microstructure, composition, optical property and mechanical property were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transformed infrared spectroscopy, and nanoindentation. The results showed that the crystal structure of Y2O3 films transformed from cubic to monoclinic with the increase of oxygen–argon ratio. Meanwhile, the degree of non-stoichiometry of the film with the monoclinic phase was higher than the film with the cubic phase. Both monoclinic and cubic Y2O3 film had an anti-reflection effect on diamond in the 8–12 μm long-wavelength infrared (LWIR) range. However, the maximum transmittance of the Y2O3 film-coated diamond was shifted to lower wavelengths, which were mainly attributed to the reflective indexes of the Y2O3 film that decreased with the increase of the oxygen–argon ratio. The Y2O3 film with a cubic phase had high resistance to abrasion and plastic deformation. Therefore, the Y2O3 film with a cubic phase was much more suitable for long-wave infrared application.