High‐rate sputtering of enhanced aluminum mirrors

Single‐layer, high‐purity Al films approximately 0.1 μm thick were made by high‐rate planar magnetron sputtering at rates above 12 nm/s. Reflectance in the visible was found to be at least as high as that reported for carefully made evaporated films. Enhanced reflectors of the standard metal/low/high design were made, with SiO2 as the low‐index material and TiO2 the high. The SiO2 was rf planar magnetron sputtered from a fused silica target, while the TiO2 was formed by reactive dc magnetron sputtering in a 85:15 argon/oxygen mixture. Deposition rates were 2 and 0.38 nm/s, respectively. The visible reflectance of these films was above 95% peak and 94% average. The results of a number of physical and environmental tests on the mirrors are reported.