Effect of MgF2 deposition temperature on Al mirrors in vacuum ultraviolet

Fengli Wang; Shuangying Li; Zhuangzhuang Zhang; Zhanshan Wang; Hongjun Zhou; Tonglin Huo

doi:10.1117/12.2540004

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8 July 2019 Effect of MgF2 deposition temperature on Al mirrors in vacuum ultraviolet

Fengli Wang, Shuangying Li, Zhuangzhuang Zhang, Zhanshan Wang, Hongjun Zhou, Tonglin Huo

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Proceedings Volume 11064, Tenth International Conference on Thin Film Physics and Applications (TFPA 2019); 110640O (2019) https://doi.org/10.1117/12.2540004
Event: Pacific Rim Laser Damage 2019 and Thin Film Physics and Applications 2019, 2019, Qingdao, China

Abstract

High reflectivity of mirrors is very important for many applications in the vacuum ultraviolet, such as for space observation, synchrotron radiation. This paper focuses on the substrate temperature’s effect on the performance of Al mirrors when depositing the upper MgF₂ layer. Al films are deposited on the substrates at room temperature by thermal evaporation, and a 5 nm MgF₂ film is deposited on Al coating at room temperature immediately. Heating the substrate to various temperatures ranging from room temperature to 350°, then a 20 nm MgF₂ film is deposited on the surface of Al/MgF₂. The thickness of each layer is characterized using grazing incidence x-ray reflectivity. The reflectivity of sample is measured at the incident angle of 5° in the wavelength range of 105~130 nm. The reflectivity of all samples fabricated at above room temperature is higher than the sample at room temperature below 115nm. The reflectivity of mirror at 350° temperature is lower than other mirrors, and the reflectivity of the samples at 300° and 200° is similar. There are more black dots on the surface of mirror at 350° than 300°, and no black dot on the surface of mirror at 200°. The measured results using surface profiler show that the black dots are small holes that increase the roughness of mirror and reduce the reflectivity. So the best temperature for depositing the upper MgF₂ layer is in 200~300° to obtain high reflectivity of Al mirrors in vacuum ultraviolet.

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Fengli Wang, Shuangying Li, Zhuangzhuang Zhang, Zhanshan Wang, Hongjun Zhou, and Tonglin Huo "Effect of MgF2 deposition temperature on Al mirrors in vacuum ultraviolet", Proc. SPIE 11064, Tenth International Conference on Thin Film Physics and Applications (TFPA 2019), 110640O (8 July 2019); https://doi.org/10.1117/12.2540004

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