Irradiation-induced broadening of the Raman spectra in monolayer graphene

TL;DR

This study investigates how ion irradiation and subsequent annealing affect the Raman spectra of monolayer graphene, revealing linear broadening of key Raman lines with defect density and developing a theoretical model to explain these effects.

Contribution

It presents the first detailed analysis of irradiation-induced Raman broadening in monolayer graphene and introduces a theoretical model linking defect density to spectral width.

Findings

Raman line widths increase linearly with defect density.

The slope of broadening is similar for G- and D-lines, double for 2D-line.

D-line width exceeds half of the 2D-line width, indicating additional scattering effects.

Abstract

Broadening of the Raman scattering (RS) spectra was studied in monolayer graphene samples irradiated with various dose of ions followed by annealing of radiation damage at different temperatures. It is shown that the width {\Gamma} (full width at half maximum, FWHM) of three main RS lines (G-, D-, and 2D) increases linearly with increase of the density of irradiation-induced point defects N d as {\Delta}{\Gamma} = m N d . The slope m of the linear dependencies is the same for one-phonon emitting G-line and D-line, and almost double for two-phonon emitting 2D-line. It is also shown that the width of D-line {\Gamma} D for all samples is larger than one half of the width of 2D-line {\Gamma} 2D , which shows that in the case of D-line, elastic electron scattering on point defects leads to an additional decreasing the lifetime of the emitted phonon. Theoretical model of the width of D-line in disordered graphene is developed which explains the experimental observations and allows to determine the numerical coefficient in the in-plane transverse optic phonon dispersion in graphene.