Using sputtering atomic layer augmented deposition (SALAD) to optimize the dielectric/metal interface, improving longevity and spectral response of protected astronomical telescopes: case study of AlOx/Ag and AlFx/Al-mirrors

Silver (Ag) and aluminum (Al) are common metal-bases for broadband telescope mirrors, but suffer from low durability. Ag, while highly reflective in the visible range, is readily corroded necessitating a protective coating like aluminum oxide (AlOx) that impairs the blue-UV response. Similarly, Al performs well from 90-2000 nm, but requires a protective coating like aluminum fluoride (AlFx), as the metal-base is readily oxidized. Optimizing the metal/dielectric interfaces of AlOx/Ag and AlFx/Al, then are necessary to create durable high-performing mirrors. Current manufacturing methods employ physical vapor deposition (PVD) and atomic layer deposition (ALD) independently; introducing failure points at the metal/dielectric interface. The study examines using sputtering atomic layer augmented deposition (SALAD) as a solution by seamlessly integrating the capabilities of PVD and ALD without breaking vacuum. Further, a focus is placed on multi-physics modeling, environmental testing, characterization, and assessment of degradation mechanisms.