Sputter deposited ultrathin Al2O3 protected silver nanoislands film as an oxidation resistant SERS substrate

Abstract

In this work, we have used radio frequency (RF) plasma for depositing an ultrathin layer of Al2O3 above Ag nanoislands film to tune the surface plasmon resonance (SPR) and to passivize the surface silver atoms from oxidizing. The surface morphology of the films show nanoislands feature with uniform film coverage on the substrate. The temporal stability of SPR is compared for both Al2O3 coated and bareAg thin films from optical absorption. In the absence of a passivizing layer the bare Ag films lose their SPR peak centered at 435 nm after a four week atmospheric storage, whereas the Al2O3 overlayer protected Ag films shows a consistent SPR with the peak maximum red shifted to 460 nm. Along with red shift, there is an increase in the strength and broadening of SPR which ranges from 360 to 550 nm. Surface-enhanced Raman studyshows the detectionof methylene blue at a concentration of 10-3 and 10-4 M from the prepared films.