Graphene-coated Si nanowires as substrates for surface-enhanced Raman scattering

Abstract

Si nanowires always exhibited no Raman enhancement for application in surface-enhanced Raman scattering (SERS). Herein, surface modifications of Si nanowires, without the presence of noble metals, were carried out to develop biocompatible SERS substrates. The treatment of hydrogen plasma on as-prepared Si nanowires leads to no enhanced Raman signals for the absorbed R6G molecules. The coatings of nanocrystalline diamond and multilayer graphene enable Raman signals to be enhanced with a reduced fluorescent background. The graphene-coated sample exhibits a much lower fluorescent background than the diamond-coated sample at a high concentration of the dye molecules. For the sample with graphene-coated Si nanowires, the minimum detection limit is 10-7 mol/L, and the enhancement factor reaches above 104. Such stable Raman enhancement is attributed to the formation of hydrogen-terminated graphene and the presence of the nanowire structure, accelerating charger transfer between graphene and the dye molecules. Importantly, the Raman enhancement is independent of the number of graphene layers. The Raman signal remains stable after exposure to the atmosphere for one month. Therefore, a new nanostructure of Si nanowires with graphene coating is developed, which shows great potential in SERS applications.