  Graphene is used as the thinnest possible spacer between gold nanoparticles
and a gold substrate. This creates a robust, repeatable, and stable
sub-nanometre gap for massive plasmonic field enhancements. White light
spectroscopy of single 80 nm gold nanoparticles reveals plasmonic coupling
between the particle and its image within the gold substrate. While for a
single graphene layer, spectral doublets from coupled dimer modes are observed
shifted into the near infra-red, these disappear for increasing numbers of
layers. These doublets arise from plasmonic charge transfer, allowing the
direct optical measurement of out-of-plane conductivity in such layered
systems. Gating the graphene can thus directly produce plasmon tuning.
