Raman spectroscopic characterization of interlayer coupling in twisted (2+2) and (3+3) layered graphenes

Multilayer graphene (MLG) produced by micro-mechanical exfoliation can usually be stacked layer by layer in a Bernal way through van der Waals coupling. During the exfoliation, a partial bilayer graphene (BLG) is folded onto the BLG flake itself to form the exfoliated twisted (2+2) LG. In this paper, we measured Raman spectra of a few pieces of twisted (2+2) LGs with different twisted angles in back-scattering at room temperature with a HR Evolution micro-Raman system. The modes on both sides of G mode were measured to be a signature to distinguish the twisted angle and determine the layer number in twisted (2+2) LGs. The further research was extended to a twisted (3+3) LG and some results obtained in the twisted (2+2) LGs were confirmed. These results provide an applicable approach to probe the interlayer coupling in twisted graphenes and thus benefit the future research studies on their fundamental physics and potential applications.