Mechanical and thermoelastic characteristics of optical thin films deposited by dual ion beam sputtering

摘要

Mechanical and thermoelastic properties of optical films are very important to ensure the performance of optical interference filters and optical coating systems. We systematically study the growth and the mechanical and thermoelastic characteristics of niobium oxide (Nb_(2)O_(5)), tantalum oxide (Ta_(2)O_(5)), and silicon dioxide (SiO_(2)) thin films prepared by dual ion beam sputtering. First, we investigate the stress (sigma), hardness (H), reduced Young's modulus (E_(r)), and scratch resistance. Second, we focus on the methodology and assessment of the coefficient of thermal expansion (CTE) and Poisson's ratio (v) using the two-substrate method. For the high refractive index films, namely, Nb_(2)O_(5) (n at 550 nm velence 2.30) and Ta_(2)O_(5) (n at 550 nm velence 2.13), we obtained H approx 6 GPa, E_(r) approx 125 GPa, CTE velence 4.9 X 10~(-6) (deg C)~(-1), v velence 0.22, and H approx 7 GPa, E_(r) approx 133 GPa, CTE velence 4.4 X 10~(-6) (deg C)~(-1), and v velence 0.27, respectively. In comparison, for SiO_(2) (n at550nm velence 1.48), these values are H approx 9.5 GPa, E_(r) approx 87 GPa, CTE velence 2.1 X 10~(-6) (deg C)~(-1), and v velence 0.11. Correlations between the growth conditions (secondary beam ion energy and ion current), the microstructure, and the film properties are discussed.