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Journal of Astronomical Telescopes, Instruments, and Systems

Corrosion barriers for silver-based telescope mirrors: comparative study of plasma-enhanced atomic layer deposition and reactive evaporation of aluminum oxide
Author(s): David M. Fryauf; Andrew C. Phillips; Nobuhiko P. Kobayashi
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Paper 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.

Paper Details

Date Published: 28 September 2015
PDF: 5 pages
J. Astron. Telesc. Instrum. Syst. 1(4) 044002 doi: 10.1117/1.JATIS.1.4.044002
Published in: Journal of Astronomical Telescopes, Instruments, and Systems Volume 1, Issue 4
Show Author Affiliations
David M. Fryauf, Univ. of California, Santa Cruz (United States)
NASA Ames Research Ctr. (United States)
Andrew C. Phillips, Univ. of California Observatories (United States)
Nobuhiko P. Kobayashi, Univ. of California, Santa Cruz (United States)
NASA Ames Research Ctr. (United States)

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