Atomic layer deposited protective coating of aluminum oxide on silver-based telescope mirror: a comparison between a pure ozone and H2O precursor

Silver-based telescope mirrors excel in the visible infrared but require protective coatings to overcome low durability. A single-layer of aluminum oxide (AlOx) deposited through atomic layer deposition (ALD) using trimethylaluminum and water (H2O) at low temperatures (∼60°C) protects the silver without adversely impacting the optical performance of the mirrors, but in environmental tests under high humidity at high temperatures, they degrade quickly. This paper compares the performance of AlOx-protected silver-based mirrors using two oxygen precursors: H2O and pure ozone (PO). Initially comparable, the reflectance of the PO-prepared samples shows a 17% improvement over those prepared with H2O after environmental testing.