Corrosion protection of silver-based telescope mirrors using evaporated anti-oxidation overlayers and aluminum oxide films by atomic layer deposition

被引:6
作者
Fryauf, David M. [1 ,2 ]
Phillips, Andrew C. [3 ]
Kobayashi, Nobuhiko P. [1 ,2 ]
机构
[1] Univ Calif Santa Cruz, Baskin Sch Engn, Santa Cruz, CA 95064 USA
[2] Univ Calif Santa Cruz, NASA, Ames Res Ctr, Adv Studies Labs,Nanostruct Energy Convers Techno, Moffett Field, CA USA
[3] Univ Calif Santa Cruz, Univ Calif Observ, Santa Cruz, CA 95064 USA
来源
LOW-DIMENSIONAL MATERIALS AND DEVICES 2016 | 2016年 / 9924卷
关键词
silver; mirror; ALD; aluminum oxide; corrosion barrier; protected silver; reflective coatings;
D O I
10.1117/12.2238749
中图分类号
TM [电工技术]; TN [电子技术、通信技术];
学科分类号
0808 ; 0809 ;
摘要
An urgent demand remains in astronomy for high-reflectivity silver mirrors that can withstand years of exposure in observatory environments. The University of California Observatories Astronomical Coatings Lab has undertaken development of protected silver coatings suitable for telescope mirrors that maintain high reflectivity at wavelengths from 340 nm through the mid-infrared spectrum. We present results on superior protective layers of transparent dielectrics produced by evaporation and atomic layer deposition. Several novel coating recipes have been developed with ion-assisted electron beam deposition (IAEBD) of various fluorides, oxides, and nitrides in combination with conformal layers of aluminum oxide (AlOx) deposited by ALD using trimethylaluminum as a metal precursor and water vapor as a reactant. Extending on our previous results demonstrating the superior durability of ALD-based AlOx top barrier layers over conventionally-deposited AlOx, this work investigates the effects on mirror barrier durability comparing different anti-oxidation materials on Ag with an identical AlOx top barrier layer deposited by ALD. Samples of coating recipes with different anti-oxidation layers undergo aggressive environmental testing, including high temperature/high humidity (HTHH), in which samples are exposed to an environment of 80% humidity at 80 degrees C for ten days in a simple test set-up. While most samples show fairly successful endurance after HTHH testing, visible results suggest that MgAl2O4, Al2O3, and AlN anti-oxidation layers offer enhanced robust protection against chemical corrosion and moisture in an accelerated aging environment, which is attributed to superior adhesion and intermolecular bonding between the Al-based anti-oxidation layers and the AlOx top barrier layer. Mirror samples are further characterized by reflectivity/absorption before and after deposition of oxide coatings. We also show that the performance of the ALD-AlOx barrier layer depends in part on the temperature of that process.
引用
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页数:8
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