Surface-enhanced Raman scattering to realize the phonon processes in Ag nanoparticles-decorated CdS thin film

Abstract

Surface-enhanced Raman spectroscopy (SERS) technique can achieve an ultra-high sensitivity (i.e., down to the single-molecule level) via coinage-metal nanostructures such as silver, gold, copper, etc. In this work, a geometry is proposed that consists of silver nanoparticles (AgNPs) decorated on cadmium chloride (CdCl2) annealed cadmium sulfide (CdS) thin film on a glass substrate. A strong SERS enhancement in AgNPs on CdCl2 annealed CdS thin films is achieved, which is twelve times larger than the scattering from the bare CdCl2 annealed CdS thin film. The improved SERS signal allows us to observe fundamental phonon processes in CdCl2 annealed CdS thin film. Moreover, a finite difference time domain (FDTD) method is used to understand the underlying SERS physics. By using the FDTD method, robust electromagnetic field localization in the nanogap between AgNPs and at the contact point of Ag NPs and CdS thin film is studied.