  In this paper, we report our study on gold (Au) films with different
thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman
scattering (SERS) substrates for the characterization of rhodamine (R6G)
molecules. We find that an Au film with a thickness of ~7 nm deposited on SLG
is an ideal substrate for SERS, giving the strongest Raman signals for the
molecules and the weakest photoluminescence (PL) background. While Au films
effectively enhance both the Raman and PL signals of molecules, SLG effectively
quenches the PL signals from the Au film and molecules. The former is due to
the electromagnetic mechanism involved while the latter is due to the strong
resonance energy transfer from Au to SLG. Hence, the combination of Au films
and SLG can be widely used in the characterization of low concentration
molecules with relatively weak Raman signals.
