Raman Fingerprint of Charged Impurities in Graphene

TL;DR

This paper demonstrates how Raman spectroscopy reveals the presence and concentration of charged impurities in graphene, showing variations in spectral features linked to doping levels and charge inhomogeneity.

Contribution

It introduces a Raman-based method to detect and quantify charged impurities and inhomogeneity in single-layer graphene samples.

Findings

Doping levels up to ~10^13 cm^-2 estimated from Raman spectra.

Charge inhomogeneity on sub-micron scales indicated by asymmetric G peaks.

Significant spectral variations linked to impurity-induced doping.

Abstract

We report strong variations in the Raman spectra for different single-layer graphene samples obtained by micromechanical cleavage, which reveals the presence of excess charges, even in the absence of intentional doping. Doping concentrations up to ~10^13 cm-2 are estimated from the G peak shift and width, and the variation of both position and relative intensity of the second order 2D peak. Asymmetric G peaks indicate charge inhomogeneity on the scale of less than 1 micron.