Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin-film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving the overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60°C to 300°C, and then the mirror samples underwent an environmental stress test at 80°C and 80% humidity for 10 days. While all the mirror samples annealed below 200°C showed negligible corrosion after undergoing the stress testing, those annealed below 160°C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200°C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation.

中文翻译：

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高性能保护银镜的临界加工温度

用于天文望远镜的银 (Ag) 反射镜由多个金属和介电薄膜组成。此外，这种银镜的最上表面需要覆盖一层保护涂层。虽然保护涂层通常在室温下沉积，并且整个反射镜也在室温下处理，但在高温下进行时，各种薄膜沉积技术提供了具有改进特性的保护涂层。因此，高性能银镜是根据新的基准设计和制造的。所得银镜在不同温度下进行退火（即，制造后退火）以研究在制造期间和/或之后引入热处理以提高受保护银镜的整体光学性能和耐久性的可行性。在我们的实验中，银镜样品通过电子束蒸发沉积，随后在 60°C 至 300°C 范围内的各种温度下退火，然后镜面样品在 80°C 和 80% 湿度下进行了 10 天的环境应力测试。虽然所有在 200°C 以下退火的镜面样品在进行应力测试后都显示出可忽略不计的腐蚀，但那些在 160°C 以下退火的镜面样品的光谱反射率与沉积后的参考样品相当或更高。相比之下，在 200°C 以上退火的镜子样品在应力测试后表现出明显的退化。综合分析表明，退火过程中Ag晶粒长大引起的分层和空隙是降解的主要机制。