Quantifying defects in graphene via Raman spectroscopy at different excitation energies

TL;DR

This study investigates how Raman spectroscopy can quantify defects in graphene at various excitation energies, providing a universal equation to determine defect density and resolving ambiguities using G peak analysis.

Contribution

It introduces a simple, energy-independent method to quantify defect density in graphene via Raman spectroscopy, accounting for excitation energy effects.

Findings

The D/G peak ratio depends strongly on excitation energy.

Maximum D/G ratio occurs at an inter-defect distance of ~3nm.

G peak analysis resolves ambiguity in defect density estimation.

Abstract

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities for a given defect density strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an inter-defect distance ~3nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.