Enhanced Raman scattering on functionalized graphene substrates

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 energy of molecular vibrations was considered together for the first time in order to explain the Raman signal enhancement. This approach enables to understand the enhancement of the Raman signal without any assumption about the uniformity of the molecules on the graphene surface and without a necessity to know the enhancement factor. The agreement between the theory and the experimental data was further demonstrated for varying excitation energy.