▎ 摘　　要

Graphene-metal hybrid systems are highly promising as a very important building block in plasmonic structure for biosensing and catalyzing applications. However, the potential and mechanism of graphene in plasmon enhancement for such hybrids are not clear enough, although the corresponding enhancement of light-matter interaction has been reported. Here, we report an ultrafast optical spectroscopy investigation of a graphene/Ag-nanoparticles (NP) hybrid structure and evidence photo-carrier transfer from graphene to the Ag-NP. More importantly, we show that the graphene layer acts as an electron reservoir, and the electrons that transfer from it to the Ag-NP greatly enhance plasmon excitations therein, thereby generating giant local electromagnetic field enhancement in its hybrid. Further, we show that this graphene-derived local electromagnetic enhancement contributes greatly to ultrasensitive (10(-13) M) surface-enhanced Raman scattering (SERS) in this hybrid. Our investigation reveals graphene's electromagnetic enhancement of SERS by uncovering an ultrafast carrier transfer mechanism in the graphene-plasmonic hybrid, and these results pave the way for the development of ultrasensitive plasmonic devices. (C) 2017 Elsevier Ltd. All rights reserved.