Thin film metallic glass broad-spectrum mirror coatings for space telescope applications

• Published in: Journal of non-crystalline solids. X 2020-09, Vol.7, p.100050, Article 100050
• Main Authors: Ștefanov, Tatiana, Maraka, Harsha Vardhan Reddy, Meagher, Philip, Rice, James, Sillekens, Wim, Browne, David J.
• Format: Article
• Language: English
• Subjects: Metallic glass; Optical mirrors; PVD; Reflectance; Sputtering; UV/Vis/near-IR
• ISSN: 2590-1591; 2590-1591
• DOI: 10.1016/j.nocx.2020.100050

The use of metallic glasses as coatings on silicon carbide substrates for applications as optical mirrors was investigated. Various alloy compositions were chosen, limited by the available method of synthesis by electric arc melting, using the rule of mixtures to predict their reflectance. After a preliminary experimental study on bulk specimens, two alloys were selected for production as thin film metallic glasses by physical vapour deposition on silicon carbide substrates. The alloy Zr44Cu40Al8Ag8 (at.%) was sputtered from a single target. In a separate co-sputtering experiment, two targets, one of Al90Ni5Y5 (at.%), the other of pure Zr, were deposited. The structure, roughness, and reflectance of the films were investigated. The measured reflection was compared with the predicted values for wavelengths between 250 nm and 2000 nm. The reflectance of the Al-based mirrors was uniform around 70% across the UV/Vis/near-IR spectrum range significantly improving that of the polished silicon carbide substrate. •Experimental study of reflectance of selected bulk alloys was carried out.•Thin film metallic glass (TFMG) mirrors were made by PVD onto SiC substrates.•Measured reflectance curves follow closely those predicted by the rule of mixtures.•Al-based amorphous mirrors display 70% uniform reflectance across UV/VIS/Near-IR.•Passing cryogenic tests, TFMG mirrors have potential for use in space telescopes.