23 September 2015 Protected and enhanced silver for mirrors: damage mechanisms and how to prevent them
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Abstract
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.
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S. Schwinde, S. Schwinde, M. Schürmann, M. Schürmann, Norbert Kaiser, Norbert Kaiser, Andreas Tünnermann, Andreas Tünnermann, } "Protected and enhanced silver for mirrors: damage mechanisms and how to prevent them", Proc. SPIE 9627, Optical Systems Design 2015: Advances in Optical Thin Films V, 96271R (23 September 2015); doi: 10.1117/12.2191216; https://doi.org/10.1117/12.2191216
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