Raman Spectroscopy of Graphene Edges

TLDR

Graphene edge orientation governs electronic properties, yet even macroscopically smooth edges can lack microscopic order. The study investigates Raman signatures of graphene edges with various crystallographic orientations and develops a real‑space theory to analyze disordered edges. The authors employ a real‑space Raman scattering theory and measure G and D peak parameters as a function of incident light polarization. Raman measurements show the D band is strongest for light polarized parallel to the edge, localized near the edge, vanishes for ideal zigzag edges, but in real samples the D/G ratio displays only weak dependence on edge orientation.

Abstract

Graphene edges are of particular interest since their orientation determines the electronic properties. Here we present a detailed Raman investigation of graphene flakes with edges oriented at different crystallographic directions. We also develop a real space theory for Raman scattering to analyze the general case of disordered edges. The position, width, and intensity of G and D peaks are studied as a function of the incident light polarization. The D-band is strongest for polarization parallel to the edge and minimum for perpendicular. Raman mapping shows that the D peak is localized in proximity of the edge. For ideal edges, the D peak is zero for zigzag orientation and large for armchair, allowing in principle the use of Raman spectroscopy as a sensitive tool for edge orientation. However, for real samples, the D to G ratio does not always show a significant dependence on edge orientation. Thus, even though edges can appear macroscopically smooth and oriented at well-defined angles, they are not necessarily microscopically ordered.