Raman Scattering at Pure Graphene Zigzag Edges

TL;DR

This study uses confocal Raman spectroscopy on hexagonal graphene holes with zigzag edges to confirm the theoretical predictions of distinct Raman signatures for pure edge chiralities, demonstrating unprecedented edge purity.

Contribution

It provides the first experimental confirmation of Raman theory predictions for pure zigzag graphene edges using anisotropic etching techniques.

Findings

Hexagonal holes exhibit edges aligned with the zigzag direction.

Raman maps show hardly any signature of mixed edge chirality.

The work confirms the validity of Raman theory for graphene edges.

Abstract

Theory has predicted rich and very distinct physics for graphene devices with boundaries that follow either the armchair or zigzag crystallographic directions. A prerequisite to disclose this physics in experiment is to be able to produce devices with boundaries of pure chirality. Exfoliated flakes frequently exhibit corners with an odd multiple of 30{\deg}, which raised expectations that their boundaries follow pure zigzag and armchair directions. The predicted Raman behavior at such crystallographic edges however failed to confirm pure edge chirality. Here, we perform confocal Raman spectroscopy on hexagonal holes obtained after the anisotropic etching of prepatterned pits using carbothermal decomposition of SiO2. The boundaries of the hexagonal holes are aligned along the zigzag crystallographic direction and leave hardly any signature in the Raman map indicating unprecedented purity of the edge chirality. This work offers the first opportunity to experimentally confirm the validity of the Raman theory for graphene edges.