Raman study on G mode of graphene for determination of edge orientation

We report a confocal Raman study on edges of single layer graphene. It is found that edge orientations could be identified by G mode besides D mode. We observe that G mode at edges of single layer graphene exhibits polar behaviors and different edges like zigzag- or armchair-dominated responses differently to the polarization of the incident laser. Moreover, G mode shows stiffening at zigzag-dominated edges, while it is softened at armchair- dominated ones. Our observations are in good agreement with recent theory (K. Sasaki, et al., J. Phys. Soc. Jpn. 79, 044603) and could be well explained by the unique properties of pseudospin at graphene edges, which lead to asymmetry of Raman active modes and non-adiabatic processes (Kohn Anomaly) at different types of edges. This work could be useful for further study on the properties of graphene edge and development of graphene-based devices.