高性能保护银薄膜反射镜的临界加工温度
Critical processing temperature for high performance protected silver thin film mirrors
摘要：
天文望远镜的银反射镜由多层金属和电介质薄膜组成。此外，这种Ag镜的最顶表面需要被保护涂层覆盖。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，但是各种薄膜沉积技术在高温下进行时提供具有改进特性的保护涂层。因此，在这项工作中，使用新的基准设计和制造了高性能的银镜。将所得的Ag镜退火（即，制造后退火）以研究在制造期间和/或之后引入热处理以改善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，Ag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，然后镜样品在80 °C和80%湿度下进行环境应力测试10天。虽然在200 °C以下退火的所有反射镜样品在经历应力测试后显示出可忽略的腐蚀，但在160 °C以下退火的那些反射镜样品呈现出与所沉积的参考样品相当或更高的光谱反射率。相比之下，在高于200 °C下退火的反射镜样品在应力测试后表现出显著的退化。综合分析表明，退火过程中Ag晶粒长大引起的分层和空洞是其退化的主要机制。
英文摘要：
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, in this work, 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 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.
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