Unsteady aerodynamic interaction in a closely-coupled turbine consistent with contra-rotation
Ultra-thin silver films (thickness below 10 nm) are of great interest as optical coatings in low emissive windows and plasmonic devices. However, producing these films has been a continuing challenge because of their tendency to form clusters rather than smooth contiguous thin films. In this work we have studied the effects of Cu, Ge and ZnS as wetting layers to achieve ultra-smooth ultra-thin silver films. The silver films (5 nm) were grown by RF sputter deposition on silicon and glass substrates using a few monolayers of the different wetting materials. SEM imaging was used to characterize the surface properties such as island formation and roughness of the films. And the optical properties, such as reflection and transmission, were measured to identify the optical impact of the different wetting layers. Then, a multi-layer silver based structure, low emissive coating was designed. The low emissive coating combines high transmittance over most visible spectrum and high reflectance over infrared spectrum. Such kind of coating is utilized as highly transparent in the visible and heat-reflective coating for the purpose of energy saving. The designed coatings were fabricated and their performances were evaluated. The comparison between the samples with different wetting layers shows that the designs with Cu wetting layer which has similar optical properties to silver produces the best overall performance. In the absence of a wetting layer, the measured optical spectra shows a significant departure from the model prediction, which we attribute primarily to the formation of silver film clusters.