Identifying the Orientation of Edge of Graphene Using G Band Raman Spectra

The electron-phonon matrix elements relevant to the Raman intensity and Kohn anomaly of the G band are calculated by taking into account the effect of the edge of graphene. The analysis of the pseudospin reveals that the longitudinal optical phonon mode undergoes a strong Kohn anomaly for both the armchair and zigzag edges, and that only the longitudinal (transverse) optical phonon mode is a Raman active mode near the armchair (zigzag) edge. The Raman intensity is enhanced when the polarization of the incident laser light is parallel (perpendicular) to the armchair (zigzag) edge. This asymmetry between the armchair and zigzag edges is useful in identifying the orientation of the edge of graphene.