Temperature Dependence of AlF3 Protection on Far-UV Al Mirrors

Coatings

Tomás de Lis¹  Belén Perea-Abarca¹  Lucía Espinosa-Yáñez¹  Carlos Honrado-Benítez¹  Nuria Gutiérrez-Luna¹  LuisVicente Rodríguez-de Marcos¹  JoséAntonio Aznárez¹  JuanIgnacio Larruquert¹ 

[1] GOLD-IO-CSIC Instituto de Óptica –Consejo Superior de Investigaciones Científicas, Serrano 144, 28006 Madrid, Spain;

关键词: mirrors;    protective coatings;    far ultraviolet;    optical properties of thin films;    space instrumentation;   

DOI  :  10.3390/coatings9070428

来源: DOAJ

【 摘 要 】

More efficient and stable far ultraviolet (FUV) mirrors will enable future space observatories. Traditional FUV mirrors are based on MgF₂-protected Al. AlF₃ has been identified as a promising substitute for MgF₂ to prevent Al oxidation. Hence, the reflectivity, stability, and morphology of AlF₃-protected Al mirrors have been investigated as a function of deposition temperature of the AlF₃ film. In this work, it is shown how AlF₃ deposition temperature is an important parameter whose optimization ultimately yields valuable throughput enhancement and improved endurance to large storage periods. Al films were deposited at room temperature (RT) and AlF₃ protective layers were deposited at temperatures ranging from RT to 350 °C. It was found that the optimum AlF₃ deposition temperature was between 200 and 250 °C, yielding the largest FUV reflectance and a better stability of the mirrors, which had been stored in a desiccator environment. Increasing AlF₃ deposition temperature resulted in an increase in film density, approaching bulk density at 250 °C. The morphology of Al and AlF₃ films as a function of AlF₃ deposition temperature was also investigated. The increase in the AlF₃ deposition temperature resulted in a decrease of both Al and AlF₃ surface roughness and in the growth of the grain width at the AlF₃ outer surface. It also resulted in a trend for the prevalent (111) planes of Al nanocrystals to orient parallel to the coating surface.

【 授权许可】

Unknown