Improving silver mirrors with aluminum oxynitride protection layers: variation in refractive index with controlled oxygen content by radiofrequency magnetron sputtering

Faiza Anjum; David M. Fryauf; Riaz Ahmad; Andrew C. Phillips; Nobuhiko P. Kobayashi

doi:10.1117/1.JATIS.4.4.044004

19 November 2018 Improving silver mirrors with aluminum oxynitride protection layers: variation in refractive index with controlled oxygen content by radiofrequency magnetron sputtering

Faiza Anjum, David M. Fryauf, Riaz Ahmad, Andrew C. Phillips, Nobuhiko P. Kobayashi

Author Affiliations +

Journal of Astronomical Telescopes, Instruments, and Systems, Vol. 4, Issue 4, 044004 (November 2018). https://doi.org/10.1117/1.JATIS.4.4.044004

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. Various protective coatings based on AlN are prepared by RF magnetron sputtering. Specific amounts of oxygen are deliberately introduced to obtain aluminum oxynitride (AlON) 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 are 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 80°C with ∼80 % relative humidity. Comprehensive analysis on the samples before and after the environmental testing indicates that AlON-based 41- and 56-nm protective layers with medium refractive index outperform similar samples using AlON with higher or lower refractive index. We suggest that the benefits of the best AlON barrier with specific refractive index are likely associated with the optical, chemical, and structural characteristics produced with sputtering conditions that yield a nitrogen/oxygen ratio of approximately one.

Citation Download Citation

Faiza Anjum, David M. Fryauf, Riaz Ahmad, Andrew C. Phillips, and Nobuhiko P. Kobayashi "Improving silver mirrors with aluminum oxynitride protection layers: variation in refractive index with controlled oxygen content by radiofrequency magnetron sputtering," Journal of Astronomical Telescopes, Instruments, and Systems 4(4), 044004 (19 November 2018). https://doi.org/10.1117/1.JATIS.4.4.044004

Received: 15 May 2018; Accepted: 25 October 2018; Published: 19 November 2018

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available