  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.
