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

TL;DR

This study uses confocal Raman spectroscopy to identify graphene edge orientations by analyzing G mode behaviors, revealing polarization dependence and frequency shifts that correlate with zigzag or armchair edges, supported by theoretical insights.

Contribution

It demonstrates that G mode Raman features can determine graphene edge orientation, providing a new method for edge characterization based on polarization and frequency shifts.

Findings

G mode exhibits polarization dependence at edges

G mode stiffens at zigzag edges and softens at armchair edges

Results align with theoretical predictions about pseudospin and Kohn anomaly effects

Abstract

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.