  The graphene-enhanced Raman scattering of Rhodamine 6G molecules on pristine,
fluorinated and 4-nitrophenyl functionalized graphene substrates was studied.
The uniformity of the Raman signal enhancement was studied by making large
Raman maps. The relative enhancement of the Raman signal is demonstrated to be
dependent on the functional groups, which was rationalized by the different
doping levels of pristine, fluorinated and 4-nitrophenyl functionalized
graphene substrates. The impact of the Fermi energy of graphene and the phonon
energy of the molecules was considered together for the first time in order to
explain the enhancement. Such approach enables to understand the enhancement
without assuming anything about the uniformity of the molecules on the graphene
surface. The agreement between the theory and our measured data was further
demonstrated by varying excitation energy.

Materials Science;Mesoscale and Nanoscale Physics;Other Condensed Matter