Interference enhancement of Raman signal of graphene

TL;DR

This paper explains the unexpectedly strong Raman signal in single-layer graphene on SiO2/Si substrates by considering interference effects of both incident and scattered light, achieving a significant enhancement factor and suggesting broader applications.

Contribution

It introduces a comprehensive interference model including Raman signal reflections, explaining the Raman intensity anomaly and providing a criterion for optimizing enhancement in thin films.

Findings

Raman intensity of graphene is enhanced by interference effects.

An enhancement factor of approximately 30 is achievable.

The model applies to other ultra-thin films and nanostructures.

Abstract

Raman spectroscopic studies of graphene have attracted much interest. The G-band Raman intensity of a single layer graphene on Si substrate with 300 nm SiO2 capping layer is surprisingly strong and is comparable to that of bulk graphite. To explain this Raman intensity anomaly, we show that in addition to the interference due to multiple reflection of the incident laser, the multiple reflection of the Raman signal inside the graphene layer must be also accounted for. Further studies of the role of SiO2 layer in the enhancement Raman signal of graphene are carried out and an enhancement factor of ~30 is achievable, which is very significant for the Raman studies. Finally, we discuss the potential application of this enhancement effect on other ultra-thin films and nanoflakes and a general selection criterion of capping layer and substrate is given.