  A particular interesting plasmonic system is that of metallic nanostructures
interacting with metal films. As the LSPR behavior of gold nanostructures (Au
NPs) on the top of a gold thin film is exquisitely sensitive to the spacer
distance of the film-Au NPs, we investigate in the present work the influence
of a few-layered graphene spacer on the LSPR behavior of the NPs. The idea is
to evidence the role of few-layered graphene as one of the thinnest possible
spacer. We first show that the coupling to the Au film induces a strong
lowering at around 507nm and sharpening of the main LSPR of the Au NPs.
Moreover, a blue shift in the main LSP resonance of about 13 nm is observed in
the presence of a few-layered graphene spacer when compared to the case where
gold nanostructures are directly linked to a gold thin film. Numerical
simulations suggest that this LSP mode is dipolar and that the hot spots of the
electric field are pushed to the top corners of the NPs, which makes it very
sensitive to surrounding medium optical index changes and thus appealing for
sensing applications. A figure of merit (FoM) of such a system (gold/graphene/
Au NPs) is 2.8, as compared to 2.1 for gold/Au NPs either a 33% sensitivity
gain and opens up new sensing strategies.
