Polarized microscopic laser Raman scattering spectroscopy for edge structure of epitaxial graphene and localized vibrational mode

Polarized microscopic laser Raman scattering spectroscopy accompanied with simulation model has been used to systematically analyze the details of the edge structures of the transferred epitaxial graphene. The evolution of the intensity ratio between the parallel polarized D band (VV) and the perpendicular polarized D band (VH) is determined, providing a spectroscopy-based method to probe the atomic scale edge structures in graphene. Based on the experimental Raman results, we develop a rather precise atomic scale edge model combining the armchair and zigzag edges along with some point defects. The calculated polarization dependent VH/VV ratios of the developed model are perfectly matched with the D band intensity ratios of the realistic graphene edges. The developed edge structures are also supported by the atomic force microscopy (AFM) measurements. Moreover, we calculate the vibrational eigenmodes of graphene with some realistic edge and disordered configurations. We find that the typical mode patterns for in-plane optical phonon modes (iTO) at the K point are localized near the armchair edges or the defects, which are conceptually well agreed with the high intensity D peak in the Raman spectra come from the iTO phonon near the K point activating by the armchair edges or the defects.