Raman spectroscopy of graphene on different substrates and influence of defects

TL;DR

This study investigates how Raman spectra of graphene vary with layer number, substrate type, and defects, revealing new insights into defect effects and substrate influence on vibrational modes.

Contribution

It provides new observations on the substrate-dependent Raman features and the first report of red-shifted G and 2D bands in graphene on ITO substrates.

Findings

Raman spectra vary with substrate and layer number.

Defects cause a blue shift in the G band up to 12 cm$^{-1}$.

Graphene on ITO shows a novel red shift in G and 2D bands.

Abstract

We show the evolution of Raman spectra with number of graphene layers on different substrates, SiO$_{2}$/Si and conducting indium tin oxide (ITO) plate. The G mode peak position and the intensity ratio of G and 2D bands depend on the preparation of sample for the same number of graphene layers. The 2D Raman band has characteristic line shapes in single and bilayer graphene, capturing the differences in their electronic structure. The defects have a significant influence on the G band peak position for the single layer graphene: the frequency shows a blue shift upto 12 cm$^{-1}$ depending on the intensity of the D Raman band, which is a marker of the defect density. Most surprisingly, Raman spectra of graphene on the conducting ITO plates show a lowering of the G mode frequency by $\sim$ 6 cm$^{-1}$ and the 2D band frequency by $\sim$ 20 cm$^{-1}$. This red-shift of the G and 2D bands is observed for the first time in single layer graphene.