Moisture retention influence on the anti-reflection properties of magnetron sputtered Low-E coating stacks with ZnSnOx top layers

Abstract

The influence on the optical properties of AR Low-E PVD coatings with silver IR-reflectors on glass substrates from the water absorption into their outer ZnSnOx dielectric layers was considered with the use of VIS/NIR-spectrophotometry. The estimations of coatings absorption shift reversibility depending on the initial contact with water duration as well as of the mechanisms responsible for the changes in optical constants of the stack’s layers, supported with the comparative analysis of experimental and modelled spectra, are reported. It was shown that the water vapour sorption within the top zinc stannate layer leads to the shift in optical qualities of the whole stack by the changes in the stack’s absorption spectrum in the visible range. This effect proved to be reversible with the water exclusion via the samples heat treatment, but only until the water diffusion into the depth of the Low-E stack reaches the Ag layers, propagating the aggregation, that can no longer be cured with the temperature impact. The change in integral visible-range absorption reaches up to ?Avis = 0.5-1 abs.% in comparison to the “as-deposited” samples, suggesting that the presented observations can be employed for VIS/NIR-spectrophotometry of such coatings for the purpose of their initial wetting determination, as well as the control of their further degradation.