Interaction between metal and graphene: Dependence on the layer number of graphene

The interaction between graphene and metal was investigated by studying the G band splitting in surface-enhanced Raman scattering (SERS) spectra of single-, bi-, and trilayer graphene. The Ag deposition on graphene induced large enhancement of the Raman signal of graphene, indicating SERS of graphene. In particular,the G band was split into two distinct peaks in the SERS spectrum of graphene. The extent of the G band splitting was 13.0 cm-1 for single-layer, 9.6 cm-1 for bilayer, and 9.4 cm-1 for trilayer graphene, whereas the G band in the SERS spectrum of a thick multilayer was not split. The average SERS enhancement factor of the G band was 24 for single-layer, 15 for bilayer, and 10 for trilayer graphene. These results indicate that there is a correlation between SERS enhancement factor and the extent of the G band splitting, and the strongest interaction occurs between Ag and single-layer graphene. Furthermore, the Ag deposition on graphene can induce doping of graphene. The intensity ratio of 2D and G bands (I 2D/IG) decreased after Ag deposition on graphene, indicating doping of graphene. From changes in positions of G and 2D bands after the metal deposition on graphene, Ag deposition induced n-doping of graphene, whereas Au deposition induced p-doping. © 2011 American Chemical Society.