Raman spectra of epitaxial graphene on SiC and of epitaxial graphene transferred to SiO2

TL;DR

This study uses Raman spectroscopy to analyze the number of layers and structural differences of epitaxial graphene on SiC and after transfer to SiO2, highlighting substrate effects and layer identification markers.

Contribution

It identifies the linewidth of the 2D peak as the key Raman fingerprint for layer determination in epitaxial graphene on SiC and compares substrate effects on Raman features.

Findings

The 2D peak linewidth unambiguously indicates layer number.

The G peak is blue-shifted due to the SiC substrate.

Transferring graphene to SiO2 preserves the broad 2D peak characteristic.

Abstract

Raman spectra were measured for mono-, bi- and trilayer graphene grown on SiC by solid state graphitization, whereby the number of layers was pre-assigned by angle-resolved ultraviolet photoemission spectroscopy. It was found that the only unambiguous fingerprint in Raman spectroscopy to identify the number of layers for graphene on SiC(0001) is the linewidth of the 2D (or D*) peak. The Raman spectra of epitaxial graphene show significant differences as compared to micromechanically cleaved graphene obtained from highly oriented pyrolytic graphite crystals. The G peak is found to be blue-shifted. The 2D peak does not exhibit any obvious shoulder structures but it is much broader and almost resembles a single-peak even for multilayers. Flakes of epitaxial graphene were transferred from SiC onto SiO2 for further Raman studies. A comparison of the Raman data obtained for graphene on SiC with data for epitaxial graphene transferred to SiO2 reveals that the G peak blue-shift is clearly due to the SiC substrate. The broadened 2D peak however stems from the graphene structure itself and not from the substrate.