Shell-isolated graphene@Cu nanoparticles on graphene@Cu substrates for the application in SERS

Abstract Graphene layers, which were used to prevent metal-molecule interactions and improve the stability of the metal nanoplasmonics, have drawn a tremendous amount of attention in SERS application. At the same time, Cu substrate is usually etched to transfer the graphene onto the target substrates. The transfer process would always be time-consuming, which severely hinders its future application. Facial fabrication of graphene-SERS (G-SERS) structure with a simple, chemically stable isolating shell on a transfer-free graphene substrate is important. Here, core–shell graphene@Cu nanoparicles (G@CuNPs) have been directly deposited onto the G@Cu substrate to form the all-sided-isolated G@CuNP/G@Cu SERS substrate using the CVD system with a designed process. Raman spectra show that G@CuNPs can dramatically suppress photobleaching and fluorescence of the probe molecules (R6G), resulting in a stronger Raman signal. Electromagnetic mechanism (EM) is the main mechanism of SERS enhanced by its localized surface plasmon resonance (LSPR). Graphene layers will not alter the EM enhancement significantly, but could offer additional chemical mechanism (CM) enhancement to improve the total SERS properties. More importantly, the stability of the G@CuNP/G@Cu substrate is improved, benefiting from that graphene layer can act as the passivation layer to inhibit the surface oxidation of the Cu nanoparticles and Cu substrate.