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Improving silver mirrors with aluminum nitride protection layers: tailoring refractive index with controlled oxygen content by RF magnetron sputtering (Conference Presentation)

Paper Abstract

According to the demand for high-performance silver-based telescope mirrors, attempts are being made to develop surface coatings that protect the mirrors from corrosion. Aluminum nitride (AlN) is utilized for various optical coatings, and its high optical transparency and mechanical robustness make it potentially well-suited as a protective coating of silver-based mirrors. However according to our best knowledge, AlN with controlled oxygen content has never been used to protect silver mirrors. In this study, various protective coatings based on AlN were prepared by RF magnetron sputtering. Specific amounts of oxygen were deliberately introduced to obtain protective layers with refractive indices within a certain range (i.e., high ~2.1, medium ~1.8, and low ~1.6 at 400 nm). The designed protective layers were applied to two types of silver-based mirror test structures, and their performance was assessed in terms of optical reflectivity and structural integrity of the test structures that underwent environmental testing in a controlled atmosphere at 80C with ~80% relative humidity. Comprehensive analysis on the samples before and after the environmental testing indicates that AlN-based protective layers with medium refractive index outperform similar samples using AlN with higher or lower refractive index., We suggest that the benefits of the best AlN barrier with specific refractive index are likely associated with the unique optical, chemical, and structural characteristics based on a unique nitrogen/oxygen ratio.

Paper Details

Date Published: 9 September 2019
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Proc. SPIE 11085, Low-Dimensional Materials and Devices 2019, 1108509 (9 September 2019); doi: 10.1117/12.2530002
Show Author Affiliations
Faiza Anjum, Government College Univ. (Pakistan)
David M. Fryauf, Univ. of California, Santa Cruz (United States)
Nobuhiko P. Kobayashi, Univ. of California, Santa Cruz (United States)


Published in SPIE Proceedings Vol. 11085:
Low-Dimensional Materials and Devices 2019
Nobuhiko P. Kobayashi; A. Alec Talin; Albert V. Davydov, Editor(s)

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