Interference Phenomenon in Graphene-Enhanced Raman Scattering

Graphene-enhanced Raman scattering (GERS) has been discovered, and the chemical enhancement mechanism based on charge transfer was thought as the main reason for the enhancement. We reported herein the effect of an interference phenomenon, a well-known reason for influencing the Raman scattering intensity, on the GERS using SiO2/Si substrates with different SiO2 thicknesses. First, it was found that the variation of Raman intensity of graphene on different thicknesses of SiO2/Si substrates followed the interference law. When the GERS system was moved on these substrates, where copper phthalocyanine (CuPc) and protoporphyrin IX (PPP) were constructed on graphene, the variation of the Raman intensity of the molecules on graphene and on SiO2/Si substrate also followed the interference law well. However, for the GERS system, the Raman intensity of the molecules is obviously enhanced compared to the molecules on SiO2/Si substrates. The results show that when we compare the Raman scattering intensity of the molecule in the GERS system and non-GERS system on a SiO2/Si substrate with the same SiO2 thickness, an interference phenomenon will not influence the comparison of the intensity. Meanwhile, charge transfer between graphene and the molecule is proven existent regardless of the thick SiO2/Si substrate on which GERS occurs, by comparing the G-band shift of graphene before and after the deposition of the molecule, which further indicates the interaction between the molecule and graphene plays an important role in GERS. This work will be beneficial for the further understanding of the origin of GERS.