Preparation and growth mechanism of a gold-coloured Ag@AAO composite film with no angular dependence

Abstract

Ag-coated anodic aluminium oxide film with a golden colour was successfully synthesized by an ultrahigh vacuum magnetron sputtering system. Free-standing Ag films were obtained by a mechanical stripping process. The results indicate that the Ag films have an ordered close-packed hexagonal pattern similar to that of the anodic aluminium oxide template. The structural colour of the sample is not derived from thin-film interference. UV–Vis reflectance spectra measurements show that the blue purple-spectrum area has a relatively strong absorption. The absorption peak indicates that the golden colour comes from localized surface plasmons. We think the reason, for the gold-coloured Ag@AAO composite film, is the periodic arrangement of Ag particles. This is also the reason why the golden colour does not change with the viewing angle. Further research shows that the Ag atoms initially grew preferentially on the hexagonal vertices of the anodic aluminium oxide template, and then Ag islands grew on the top of the anodic aluminium oxide surface, finally forming narrow Ag nanoholes on top of the wider pores of the template below, with increasing Ag sputtering time. These films show the promise of application in many areas, including decoration, display and anti-counterfeiting.