Advanced protection against environmental degradation of silver mirror stacks for space application

doi:10.1016/j.jmst.2020.01.019

Abstract

Abstract:

Protection of silver mirror stacks from environmental degradation before launching is crucial for space applications. Hereby, we report a comparative study of the advanced protection of silver mirror stacks for space telescopes provided by SiO2 and Al2O3 coatings in conditions of accelerated aging by sulfidation. The model silver stack samples were deposited by cathodic magnetron sputtering on a reference silica substrate for optical applications and a surface-pretreated SiC substrate. Accelerated aging was performed in dry and more severe wet conditions. Optical micrographic observations, surface and interface analysis by Time-of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and reflectivity measurements were combined to comparatively study the effects of degradation. The results show a lower kinetics of degradation by accelerated aging of the stacks protected by the alumina coating in comparable test conditions.

Key words: Mirror layers, Protection, Layers, Silver, Atmospheric corrosion, Accelerated aging, Surface analysis, Space applications

Rajendra Kurapati, Vincent Maurice, Antoine Seyeux, Lorena H. Klein, Dimitri Mercier, Grégory Chauveau, Catherine Grèzes-Besset, Loïc Berthod, Philippe Marcus. Advanced protection against environmental degradation of silver mirror stacks for space application[J]. J. Mater. Sci. Technol., 2021, 64: 1-9.

Figures/Tables 8

Fig. 1. Optical images of multilayer stacks SiO2/Ag/SiOx ((a) 0 h; (b) 96 h, in the center; (c) 96 h, at the edge)) and SiO2/Ag/AlOx ((d) 0 h; (e) 96 h, in the center; (f) 96 h, at the edge)) before (0 h) and after (96 h) dry accelerated aging in H2S gas at 1000 mbar and 75 °C.

Fig. 2. (Color online) ToF-SIMS chemical maps (100 μm × 100 μm) of selected negative secondary ions for multilayer stacks SiC CVD/Ag/SiOx (a) and SiC CVD/Ag/AlOx (b) after 96 h of dry accelerated aging in H2S gas at 1000 mbar and 75 °C. The images are recorded in the sample center region, away from the edges.

Fig. 3. ToF-SIMS elemental depth profiles of selected negative secondary ions for multilayer stacks SiO2/Ag/SiOx (a) and SiO2/Ag/AlOx (b) after 96 h of dry accelerated aging in H2S gas at 1000 mbar and 75 °C. The profiles were recorded in the sample center region, away from the edges. The protection layer, silver (Ag) layer and substrate regions are marked, as well as the interfacial Ia and Ib regions.

Fig. 4. Optical images of multilayer stacks SiC CVD/Ag/SiOx ((a) 0 h; (b) 96 h, in the center; (c) 96 h, at the edge) and SiC CVD/Ag/AlOx ((d) 0 h; (e) 96 h, in the center; (f) 96 h, at the edge) before (0 h) and after (96 h) dry accelerated aging in H2S gas at 1000 mbar and 75 °C.

Fig. 5. ToF-SIMS chemical maps (100 μm × 100 μm) of selected negative secondary ions for multilayer stacks SiC CVD/Ag/SiOx (a) and SiC CVD/Ag/AlOx (b) after 96 h of dry accelerated aging in H2S gas at 1000 mbar and 75 °C. The images are recorded near the sample center region, away from the edges.

Fig. 6. ToF-SIMS elemental depth profiles of selected negative secondary ions for multilayer stacks SiO2/Ag/SiOx (a) and SiO2/Ag/AlOx (b) after 96 h of dry accelerated aging in H2S gas at 1000 mbar and 75 °C. The profiles are recorded near the sample center region, away from the edges. The protection layer, silver (Ag) layer and substrate regions are marked, as well as the interfacial Ia and Ib regions.

Fig. 7. Optical images of multilayer stacks SiC CVD/Ag/SiOx (a) and SiC CVD/Ag/AlOx (b) before (0 h) and after (2,4, 6 and 8 h) wet accelerated aging in 1 mM Na2S aqueous solution at pH 13 ((a) all rows and (b) first row) and pH 7 ((b) the second to last row). Center and right column images are recorded in two different sample locations.

Fig. 8. Specular reflectance spectra for stacks SiC CVD/Ag/SiOx (a) and SiC CVD/Ag/AlOx (b) before and after wet accelerated aging in 1 mM Na2S aqueous solution at pH 13 (a) and pH 7 (b).

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