Ground and Space-Based Telescopes

Corrosion barriers for silver-based telescope mirrors: comparative study of plasma-enhanced atomic layer deposition and reactive evaporation of aluminum oxide

[+] Author Affiliations
David M. Fryauf, Nobuhiko P. Kobayashi

University of California Santa Cruz, Baskin School of Engineering, 1156 High Street, Santa Cruz, California 95064, United States

University of California Santa Cruz—NASA Ames Research Center, Nanostructured Energy Conversion Technology and Research, Advanced Studies Laboratories, Moffett Field, California 94035, United States

Andrew C. Phillips

University of California, University of California Observatories, 1156 High Street, Santa Cruz, California 95064, United States

J. Astron. Telesc. Instrum. Syst. 1(4), 044002 (Sep 28, 2015). doi:10.1117/1.JATIS.1.4.044002
History: Received June 2, 2015; Accepted August 27, 2015
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Abstract.  Astronomical telescopes continue to demand high-endurance high-reflectivity silver (Ag) mirrors that can withstand years of exposure in Earth-based observatory environments. We present promising results of improved Ag mirror robustness using plasma-enhanced atomic layer deposition (PEALD) of aluminum oxide (AlOx) as a top barrier layer. Transparent AlOx is suitable for many optical applications; therefore, it has been the initial material of choice for this study. Two coating recipes developed with electron beam ion-assisted deposition (e-beam IAD) of materials including yttrium fluoride, titanium nitride, oxides of yttrium, tantalum, and silicon are used to provide variations in basic Ag mirror structures to compare the endurance of reactive e-beam IAD barriers with PEALD barriers. Samples undergo high temperature/high humidity environmental testing in a controlled environment of 80% humidity at 80°C for 10 days. Environmental testing shows visible results suggesting that the PEALD AlOx barrier offers robust protection against chemical corrosion and moisture permeation. Ag mirror structures were further characterized by reflectivity/absorption before and after deposition of AlOx barriers.

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© 2015 Society of Photo-Optical Instrumentation Engineers

Citation

David M. Fryauf ; Andrew C. Phillips and Nobuhiko P. Kobayashi
"Corrosion barriers for silver-based telescope mirrors: comparative study of plasma-enhanced atomic layer deposition and reactive evaporation of aluminum oxide", J. Astron. Telesc. Instrum. Syst. 1(4), 044002 (Sep 28, 2015). ; http://dx.doi.org/10.1117/1.JATIS.1.4.044002


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