Investigation of SiO_2-Al_2O_3 nanolaminates for protection of silver reflectors

Schwinde, Stefan; Schürmann, M.; Kaiser, Norbert; Tünnermann, Andreas

doi:10.1364/ao.56.000c41

Cited by 15 publications

(4 citation statements)

References 10 publications

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“…Despite Ag is noble element, some elements like Cl, S, O promote its corrosion. A number of protective dielectric coating designs have been suggested [32,33], consisting of one or more barrier layers over Ag surface, in order to avoid rapid Ag reflectivity degradation. Yet, even in the case of protected Ag, the appearance of defects, which decrease the reflectivity, was reported [34].…”

Section: Protection Of the Ag Reflecting Layer Against Hydrothermal C...mentioning

confidence: 99%

Large-scale collecting mirrors for ITER optical diagnostic

Samsonov¹,

Tereschenko²,

Mukhin³

et al. 2022

Nucl. Fusion

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The challenges of large-scale mirror design for in-vessel collection system of ITER Divertor Thomson Scattering (DTS) are under consideration. These are the mirrors located out-of-line vision of fusion plasma (so called “second mirrors” i.e. not First Mirrors) with high-reflective Ag-based coating. The paper outlines: approaches providing optical surface shape and angular position stability; Ag coating applicability in nuclear irradiation, ITER in-vessel application and its resistance to Steam Ingress. Although, this assessment and the proposed solutions are considered in terms of ITER DTS compatibility, they may also appear to be of some use in other ITER diagnostics and in diagnostics of other fusion devices.

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Section: Protection Of the Ag Reflecting Layer Against Hydrothermal C...mentioning

confidence: 99%

Large-scale collecting mirrors for ITER optical diagnostic

Samsonov¹,

Tereschenko²,

Mukhin³

et al. 2022

Nucl. Fusion

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“…Currently, a number of different materials are used for the thin film protective coatings, including Al 2 O 3 , TiO 2 , HfO 2 , Y 2 O 3 , Nb 2 O 5 , Ta 2 O 5 , SiO 2 , SiON x and Si 3 N 4 , as single films or in stacks [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Most of them are magnetron sputtered, but also ion-beam sputtered, evaporated with ion assistance and deposited with atomic layer deposition (ALD).…”

Section: Introductionmentioning

confidence: 99%

PECVD SiNx Thin Films for Protecting Highly Reflective Silver Mirrors: Are They Better Than ALD AlOx Films?

et al. 2021

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Protection of silver surface from corrosion is an important topic, as this metal is highly susceptible to damage by atomic oxygen, halogenated, acidic and sulfur-containing molecules. Protective coatings need to be efficient at relatively small thicknesses, transparent and must not affect the surface in any detrimental way, during the deposition or over its lifetime. We compare PECVD-deposited SiNx films to efficiency of ALD-deposited AlOx films as protectors of front surface silver mirrors against damage by oxygen plasma. Films of different thickness were deposited at room temperature and exposed to O2 ECR-plasma for various durations. Results were analyzed with optical and SEM microscopy, pulsed GD-OES, spectroscopic ellipsometry and spectrophotometry on reflection. Studies indicate that both films provide protection after certain minimal thickness. While this critical thickness seems to be smaller for SiNx films during short plasma exposures, longer plasma treatment reveals that the local defects in PECVD-deposited films (most likely due to erosion of some regions of the film and pinholes) steadily multiply with time of treatment and lead to slow drop of reflectance of SiNx-protected mirrors, whereas we showed before that ALD-deposited AlOx films reliably protect silver surface during long plasma exposures.

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“…In addition to a high resistance to liquid solutions, the protective layer of an Ag coating should have a low mechanical stress. Tensile stresses can lead to cracks in the protective layer, and compressive stresses can lead to delamination of the protective layer [18][19][20]. Both, cracks or delamination, lead to a damage of the protected Ag-coating and result in a decrease of specular reflectivity.…”

Section: Introductionmentioning

confidence: 99%

Protected silver coatings for reflectors

Schwinde

Schürmann

Schlegel

et al. 2019

International Conference on Space Optics — ICSO 2018

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For ground-and spaced based applications, Ag coated reflectors are indispensable because of their high reflectivity. The transport, assembling and storage of these reflectors takes a long time, before they are finally commissioned for the actual applications. To endure this period without a decrease of reflectivity, protective coatings with a final layer, which offers a high resistance to aqueous solutions and a low mechanical stress should be used. These criteria were taken into account for the selection of a final layer for a protected Ag-coating, which was applied for reflectors utilized in the CRIRES +instrument (an IR spectrograph used at the VLT). Reactively sputtered Al2O3, SiO2 and Si3N4 layers were investigated with regard to these criteria. In aqueous (basic) solutions, the investigated Si3N4 layers are more stable than the SiO2 layers, and the SiO2 layers are more stable than the Al2O3 layers. This shows the influence of the intrinsic material properties. The mechanical stress of the sputtered layers depends on the deposition conditions and thus on the selected parameters. A Si3N4 layer with a high resistance to aqueous solutions also offers a low and stable mechanical stress. Therefore, the depositionparameters which have been used for this layer were applied for sputtering the final layer of the protected Ag-coating for the reflectors.

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Investigation of SiO_2-Al_2O_3 nanolaminates for protection of silver reflectors

Cited by 15 publications

References 10 publications

Large-scale collecting mirrors for ITER optical diagnostic

Large-scale collecting mirrors for ITER optical diagnostic

PECVD SiNx Thin Films for Protecting Highly Reflective Silver Mirrors: Are They Better Than ALD AlOx Films?

Protected silver coatings for reflectors

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