Ni–Cr passivation of very thin Ag films for low-emissivity multilayer coatings

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Abstract
In the present work, the optical properties in the visible and infrared ranges of glass/SnO2(380 Å)/Ni–Cr(15 Å)/Ag(90 Å)/Ni–Cr(25 Å)/SnO2(380 Å) and glass/SnO2(380 Å)/Ni–Cr(15 Å)/Ag(90 Å)/SnO2(380 Å) systems are compared in order to determine the influence of the external Ni–Cr film on the optical behavior of low-emissivity multilayer coatings for energy saving applications. It has been observed that the lack of either one Ni–Cr film results in the hampering of the low-emissivity behavior (from 2.5% to 49.5% at λ=10 μm), as a result of the diminution of the reflectance values in the infrared range (from 97.5% to 50.5% at λ=10 μm). The lack of the Ni–Cr film also affects the optical performance in the visible range, by decreasing the transmittance from approximately 80% to 60% at λ=550 nm, and increasing the reflectance from about 5% to 30%. This behavior is attributed to the partial oxidation of the silver layer which might result both in a variation of the chemical and structural properties of this film.