Effect of oxygen/argon ratio on microstructure, compositon and optical properties of erbium oxide anti-reflection films on CVD diamond

Abstract

Optical erbium oxide (Er2O3) films were prepared by radio frequency (RF) magnetron sputtering to improve the infrared (IR) transmittance of chemical vapor deposition (CVD) diamond. This study aims to analyze the microstructure, composition and optical properties of Er2O3 anti-reflection films at various oxygen/argon ratios. Atomic force microscopy (AFM) analysis was used to detect the surface morphology of chemical oxidation CVD diamond and Er2O3 films. The surface roughness of Er2O3 films decreased with an increase in the oxygen/argon ratio. The crystalline structure of Er2O3 films was analyzed by using X-ray diffraction. Meanwhile, a gradual decrease was observed when the crystallite size and its strain were calculated. This was due to the transformation of partial phases from monoclinic to cubic structures. The chemical composition of Er2O3 films was analyzed by X-ray photoelectron spectroscopy (XPS). The surface of Er2O3 films underwent a transformation from the unstable structure of nonstoichiometric Er2O3-x to the stable structure of Er2O3 with an increase in the level of oxygen. Defect behavior was determined by transmission electron microscopy (TEM). Specifically, dislocation and twinning were observed at a high oxygen/argon ratio, which was mainly attributed to the competitive growth of polycrystalline Er2O3 films. The optical constants of Ψ and △ were shifted to lower wavelengths with increase oxygen/argon ratio. The maximum transmittance of the Er2O3/diamond film was 79% in the long-wavelength infrared (LWTR) range of 8–12 μm at an oxygen/argon ratio of 1:35. This value was significantly higher than that of the high oxygen/argon ratio. The present study concludes that a low oxygen/argon ratio promotes the growth and IR transmittance of Er2O3 films.