The evolution of Raman spectrum of graphene with the thickness of SiO2 capping layer on Si substrate

In this paper, we have systematically studied the evolution of Raman spectrum of graphene with the thickness of SiO2 capping layer on Si substrate. We find that, for both monolayer and bilayer graphenes, the intensities of D, G, and 2D bands, together with the intensity ratio of 2D to G Raman bands (I-2D/I-G), oscillate quasi-periodically with SiO2 thickness increasing. The origin of the observed phenomena is theoretically analyzed. Our result shows that one must pay enough attention to the SiO2 thickness when using the Raman footprints, especially the commonly used I-2D/I-G, to identify the graphene layers transferred onto SiO2/Si substrate. (C) 2013 AIP Publishing LLC.