Metal nanolayer deposited highly stable Ag thin films and their optical properties

Silver (Ag) is a material with excellent electrical, optical and thermal properties. However, Ag thin films readily agglomerate and become rough or even discontinuous films by heat treatment, because of the easy migration of... [ view full abstract ]

Silver (Ag) is a material with excellent electrical, optical and thermal properties. However, Ag thin films readily agglomerate and become rough or even discontinuous films by heat treatment, because of the easy migration of Ag atoms. We have developed thermally stable Ag thin film structures where Ag film is sandwiched with surface and interface metal nanolayers, for example, Al/Ag/Al structure. The deposited Al metal nanolayer becomes Al oxide nanolayer by natural oxidation. This is a simple and convenient method to prepare oxide nanolayer, which can avoid any damage to surface of the Ag film.

In the present study, we investigated optical properties of the multilayers. It is known that Al film shows lower reflectance than Ag film except ultraviolet region. On the other hand, Al oxide is transparent, which may give no influence on reflectance. Therefore, objective of the study is to investigate influence of the Al surface layer on reflectance. We compared the properties of same multilayer structures by different deposition methods.

 We prepared multilayers consisting of Al surface layer and Ag thin film by rf sputtering (SP) and vacuum evaporation (EV). The films were deposited on glass substrates. The obtained films were characterized using XRD, AFM, and the optical reflectance spectra were measured by a spectrophotometer.    As an influence of Al nanolayer on the specular reflectance, the reflectance of Al/Ag multilayer were almost the same as Ag films where Al thickness was 1 nm (SP) and 1 and 3 nm (EV). It is considered that Al surface layer was fully oxidized where the thickness was 1 nm, but Al remains in metal state where the thickness was further increased. In conclusion, we confirmed that metal nanolayer deposited Ag films which possess high thermal stability, also achieve high optical reflectance.