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Protected and enhanced silver for mirrors: Damage mechanisms and how to prevent them

: Schwinde, S.; Schürmann, M.; Kaiser, N.; Tünnermann, A.


Lequime, Michel (Ed.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Systems Design 2015 : Advances in Optical Thin Films V, 7-10 September 2015, Jena, Germany
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9627)
ISBN: 978-1-62841-816-3
Paper 96271R, 6 pp.
Conference "Advances in Optical Thin Films" <5, 2015, Jena>
Conference "Optical Systems Design" <2015, Jena>
Conference Paper
Fraunhofer IOF ()

In order to manufacture mirrors metal based coatings (Al, Au and Ag) are applied, as they enable a high reflectivity and at the same time a broad spectral bandwidth. Of all metals, Ag provides the highest reflectivity from VIS to IR.
Silver is a noble metal. However, corrosion activators (e.g. S and Cl) can lead to corrosion. Thus, a protective layer is required to prevent the corrosion and sustain the high reflectivity of the mirror. However, damage of the Ag-coating can occur, even in the case of protected-Ag. Inhomogeneous film growth of the protective layer can lead to a permeation of corrosion activators and thus to a damage of the Ag. But also the deposition of impervious protective layers is not sufficient for long-term environmental stability. Hygroscopic air borne particles can weaken the protection and therefore subsequently lead to a permeation of corrosion activators and thus to a damage of the Ag.
These damage mechanisms lead to criteria for a durable and efficient protection. AlOxNy and nanolaminates have been tested with respect to these criteria. In particular the protection based on nanolaminates shows a great potential for the protection of Ag. In addition, also the optical performance can be improved by UV-enhancement based on different nanolaminates.