Raman scattering study on graphene and its derivatives.

Abstract

In this project, graphene and its derivative-chemically decorated graphene (with R6G) will be investigated by confocal micro-Raman spectroscopy. The interaction between electron and phonon in graphene and its derivative will be the main focus. Graphene is a monolayer of carbon atoms packed into a two-dimensional (2D) honeycomb crystal structure, which is a special material with many excellent properties. In this project, the possibility that graphene can be used as a substrate for enhancing Raman signals of adsorbed molecules will be discussed. Here, rhodamine 6G (R6G), which is a popular molecule widely used as a Raman probe, is deposited equally on graphene and a SiO2/Si substrate using solution soaking. By comparing the Raman signals of molecules on monolayer graphene and on a SiO2/Si substrate, we observed that the intensities of the Raman signals on monolayer graphene are much stronger than on a SiO2/Si substrate, indicating a clear Raman enhancement effect on the surface of monolayer graphene. What’s more, the intensities of decrease with an increase in the number of the layers of graphene and eventually the signals can no longer be seen on graphite. Furthermore, the Raman enhancement factors are also found to be quite different for peaks that correspond to different symmetries of vibrations of the molecule. We attribute this enhancement to the charge transfer between graphene and the molecules, which result in a chemical enhancement. Further research has also been done in this project to understand this special phenomenon. The obtained results also suggest that by scanning AFM images of R6G molecules on graphene, it is possible to distinguish the armchair and zigzag directions in graphene. These new phenomena for graphene will expand its application to microanalysis and is good for studying the basic properties of both graphene and SERS.