Effect of ionic oxygen concentration on properties of SiO2 and Ta2O5 monolayers deposited by ion beam sputtering

Abstract

Optical thin films with ultralow absorption loss are crucial for high-precision optical systems. The ionic oxygen concentration and oxygen flow rate play decisive roles in the absorption loss of the film. We prepared SiO2 and Ta2O5 monolayers using a double-ion beam sputtering (DIBS) deposition system and studied the effects of different ionic oxygen concentrations and oxygen flow rates on the optical constants, weak absorption, –OH defects, and dispersion energy parameters. The results show that the oxygen flow slightly affects the weak absorption of SiO2 films, while a higher ionic oxygen concentration facilitates the reduction of the absorption loss of SiO2 films, resulting in fewer –OH defects. A higher ionic oxygen concentration decreases the refractive index of the Ta2O5 films. The relatively low lattice permittivity of the Ta2O5 films may be attributed to the argon bubbles wrapped in the film. Annealing can reduce the absorption of the film but cannot improve its surface roughness. A Ta2O5/SiO2 high-reflection film was produced with an optimal ionic oxygen concentration and oxygen flow rate, with the lowest absorption loss for both materials. The weak absorption attained 1.4 ppm, playing a significant role in improving the performance of the high-power and high-precision optical systems.