Size-Dependent Surface-Enhanced Raman Scattering Activity of Ag@CuxOS Yolk–Shell Nanostructures: Surface Plasmon Resonance Induced Charge Transfer

Ag@CuxOS yolk–shell nanoparticles with hollow shells were designed through an ion-exchange route from Au@Cu2O nanoparticles. This isolated yolk–shell structure can be used to overcome the material limitations and generality of a surface-enhanced Raman scattering (SERS) morphology. Both surface plasmon resonance (SPR) and charge-transfer (CT) contributions increase when the diameter of the Ag@CuxOS nanoparticles decreases. Because of the SPR effect of Ag upon irradiation with incident light, the induced hot electrons were injected into 4-mercaptobenzoic acid through the CuxOS shell to complete the CT transition. SERS is an effective and simple method for studying the SPR effect at the nanomaterial interface, which is a good candidate method for investigations of interfacial CTs. Furthermore, 2D correlation SERS spectroscopy was performed to confirm the possible CT process and to support our proposed conclusion. The design and fabrication of a SERS-active metal and semiconductor core–shell nanostructures may provide a strategy to overcome the limitations associated with the performance of a single material.