Abstract:In this work, we addressed the local degradation mechanisms limiting the prelaunch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on lightweight SiC substrates and protected by thin SiO overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous HS. The res… Show more
“…They confirmed that the surface porosity characterizing the SiC substrate and originating from the material production process is suppressed by the CVD surface treatment like specified by the provider. On the SiC substrate ( Figure 1(a,b)), the lateral dimensions (0.5-6 µm), depth (0.05-0.4 µm) and density (~1.6×10 6 cm -2 ) of the surface pores remain essentially unchanged after deposition of the stacks, showing that the pores remain incompletely filled and that the surface still exhibits high aspect ratio topographic sites as discussed previously [35]. On the SiC+CVD substrate (Figure 1(d…”
Section: Methodssupporting
confidence: 57%
“…Accelerated atmospheric aging was performed in gaseous H2S selected as most corrosive indoor atmospheric agent of silver. The accelerated aging tests were performed at 1000 mbar H2S and 75°C for 24, 48 and 96 h, like previously described [35]. The sulfurized samples were transferred through air for surface analysis.…”
Section: Methodsmentioning
confidence: 99%
“…Starting from the outer surface, they allow us defining the following five regions (all marked): the protection layer region (using the SiOand 18 Oions), the adhesion interfacial layer Ia, the silver mirror layer and the adhesion interfacial layer Ib regions (all three using the Agions) and the SiC substrate region (using the SiCand Cions). The Ia and Ib interfacial layer regions can also be defined using their respective ions as reported previously [35].…”
Section: Depth Profiling Of As-received Stacksmentioning
confidence: 99%
“…It has been shown that a H2S concentration as low as 0.2 ppb is sufficient to initiate silver sulfidation [28]. Degradation studies performed on space silver mirrors mostly addressed the efficiency of the protection layer and the effect of environmental aging on the optical properties [10,15,25,[29][30][31], and more seldom their tarnishing mechanism [32][33][34][35].…”
Section: Introductionmentioning
confidence: 99%
“…In a recent work [35], we studied model stack samples consisting of thin silver layers covered by SiO2 coatings deposited by cathodic magnetron sputtering on SiC, a substrate already in use in light weight all-SiC telescopes assigned to scientific or earth observation missions. These stacks were submitted to accelerated aging in H2S gas and studied by combined surface and interface analysis using Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Time-of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).…”
The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer.
“…They confirmed that the surface porosity characterizing the SiC substrate and originating from the material production process is suppressed by the CVD surface treatment like specified by the provider. On the SiC substrate ( Figure 1(a,b)), the lateral dimensions (0.5-6 µm), depth (0.05-0.4 µm) and density (~1.6×10 6 cm -2 ) of the surface pores remain essentially unchanged after deposition of the stacks, showing that the pores remain incompletely filled and that the surface still exhibits high aspect ratio topographic sites as discussed previously [35]. On the SiC+CVD substrate (Figure 1(d…”
Section: Methodssupporting
confidence: 57%
“…Accelerated atmospheric aging was performed in gaseous H2S selected as most corrosive indoor atmospheric agent of silver. The accelerated aging tests were performed at 1000 mbar H2S and 75°C for 24, 48 and 96 h, like previously described [35]. The sulfurized samples were transferred through air for surface analysis.…”
Section: Methodsmentioning
confidence: 99%
“…Starting from the outer surface, they allow us defining the following five regions (all marked): the protection layer region (using the SiOand 18 Oions), the adhesion interfacial layer Ia, the silver mirror layer and the adhesion interfacial layer Ib regions (all three using the Agions) and the SiC substrate region (using the SiCand Cions). The Ia and Ib interfacial layer regions can also be defined using their respective ions as reported previously [35].…”
Section: Depth Profiling Of As-received Stacksmentioning
confidence: 99%
“…It has been shown that a H2S concentration as low as 0.2 ppb is sufficient to initiate silver sulfidation [28]. Degradation studies performed on space silver mirrors mostly addressed the efficiency of the protection layer and the effect of environmental aging on the optical properties [10,15,25,[29][30][31], and more seldom their tarnishing mechanism [32][33][34][35].…”
Section: Introductionmentioning
confidence: 99%
“…In a recent work [35], we studied model stack samples consisting of thin silver layers covered by SiO2 coatings deposited by cathodic magnetron sputtering on SiC, a substrate already in use in light weight all-SiC telescopes assigned to scientific or earth observation missions. These stacks were submitted to accelerated aging in H2S gas and studied by combined surface and interface analysis using Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Time-of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).…”
The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer.
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