Effects of different wetting layers on the growth of smooth ultra-thin silver thin films

Abstract

Ultrathin silver films (thickness below 10 nm) are of great interest as optical coatings on windows and plasmonic devices. However, producing these films has been a continuing challenge because of their tendency to form clusters or islands rather than smooth contiguous thin films. In this work we have studied the effect of Cu, Ge and ZnS as wetting layers (1.0 nm) to achieve ultrasmooth 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. Also the optical properties were measured to identify the optical impact of the different wetting layers. Finally, a multi-layer silver based structure is designed and fabricated, and its performance is evaluated. The comparison between the samples with different wetting layers show that the designs with wetting layers which have similar optical properties to silver produce the best overall performance. In the absence of a wetting layer, the measured optical spectra show a significant departure from the model predictions, which we attribute primarily to the formation of clusters.

Two-Step Approach for Conformal Chemical Vapor-Phase Deposition of Ultra-Thin Conductive Silver Films

“…The use of a wetting layer has demonstrated strong improvement for the growth of ultra-thin continuous metal films (see detailed review in refs and ). Although good results were obtained in the case of line-of-sight techniques, − ,− only noncontinuous films or a slight enhancement of the coverage were observed when chemical vapor-phase methods were engaged. A two-step approach consisting of the deposition of a metal-containing film subsequently reduced to a metallic state was proved for copper thin layers. , However, this will be difficult to transfer to silver coatings as stable Ag (II) complexes are extremely complex to obtain, mainly due to their more noble character as compared to Cu.…”