Quantifying Defects in Graphene via Raman Spectroscopy at Different Excitation Energies

TLDR

Controlled Ar⁺ ion bombardment provides a systematic way to introduce increasing defect densities in graphene. The study aims to quantify defect density in graphene using Raman spectroscopy across visible excitation energies. This is achieved by bombarding graphene with Ar⁺ ions at varying doses and measuring the D and G peak intensities to derive a simple equation. The D/G intensity ratio varies strongly with laser energy, peaks when the interdefect distance is ~3 nm, and can correspond to two defect densities; analysis of the G‑peak width and its dispersion with energy resolves this ambiguity.

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 interdefect distance ∼3 nm. 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.