Correlative Raman Imaging and Scanning Electron Microscopy: the Role of Single Ga Islands in Surface-Enhanced Raman Spectroscopy of Graphene

TL;DR

This study combines Raman imaging and electron microscopy to analyze how single gallium islands on graphene enhance Raman signals through localized surface plasmon resonances, revealing size-dependent effects.

Contribution

It introduces a correlative approach to link the shape and size of individual Ga islands with their plasmonic Raman enhancement, advancing understanding of SERS mechanisms.

Findings

Raman peaks are enhanced by single Ga islands.

Enhancement depends on island size, peaking at medium sizes.

Simulation results agree with experimental data.

Abstract

Surface enhanced Raman spectroscopy (SERS) is a perspective non-destructive analytic technique enabling detection of individual nanoobjects, even single-molecules. . In the paper, we have studied the morphology of Ga islands deposited on CVD graphene by ultrahigh vacuum (UHV) evaporation and local optical response of this system by the correlative Raman Imaging and Scanning Electron Microscopy (RISE). Contrary to the previous papers, where only an integral Raman response from the whole ununiformed Ga NPs ensembles on graphene was investigated, the RISE technique has enabled us to detect graphene Raman peaks enhanced by single Ga islands and particularly to correlate the Raman signal with the shape and size of these single particles. In this way and by a support of numerical simulations, we have proved a plasmonic nature of the Raman signal enhancement related to localized surface plasmon resonances (LSPR). It has been found that this enhancement is island-size dependent and shows a maximum for medium-sized Ga islands. A reasonable agreement between the simulations of the plasmon enhancement of electric fields in the vicinity of Ga islands and the experimental intensities of corresponding Raman peaks proved the plasmonic origin of the observed effect known as the Surface Enhanced Raman Spectroscopy.