Improved durability of Ag thin films under high humidity environment by deposition of surface Al nanolayer

摘要

Silver exhibits the highest reflectance from the visible to the infrared region however, its low durability is also well known. In this study, Al nanolayers were deposited on Ag thin films (Al/Ag) by vacuum evaporation, where a 1 nm thick or 3 nm thick Al layer was deposited on Ag film. The durability of the Al/Ag films under high humidity was investigated by holding the samples at 55 degrees C, 90% relative humidity (RH) for 6 h. After the test, remarkable agglomeration occurred in the Ag single film, but not in Al/Ag films. Therefore, the passivation effect of the Al oxide nanolayer, which was formed by natural oxidation of the Al nanolayer, was confirmed. This effect also meant that the optical reflectance was kept high, even after the test. Without the Al surface layer, diffuse reflectance caused by roughening of the film was significantly large. The humidity test was carried out in air, so that sulfide was formed at the surface of the Ag single film, but not formed on the Al oxide surface layer. As a result, a several nanometer thick passivation layer was determined to improve the durability of the Ag layer and maintain high reflectance.