  Graphene-metal nanoparticle hybrid materials potentially display not only the
unique properties of metal nanoparticles and those of graphene, but also
additional novel properties due to the interaction between graphene and
nanoparticles. This study shows that gold nanoislands can be used to tailor the
local electronic properties of graphene. Graphene on crystalline gold
nanoislands exhibits moir\'e superlattices, which generate secondary Dirac
points in the local density of states. Conversely, the graphene covered gold
regions undergo a polycrystalline to Au(111) phase transition upon annealing.
Moreover, the nanoscale coexistence of moir\'e superlattices with different
moir\'e periodicities has also been revealed. Several of these moir\'e
periodicities are anomalously large, which cannot be explained by the standard
lattice mismatch between the graphene and the topmost Au(111) layers. Density
functional theory and molecular dynamics simulations show for the first time
that in such cases the graphene and the interfacial metallic layer is strained,
leading to distorted lattice constants, and consequently to reduced misfit.
Room temperature charge localization induced by a large wavelength moir\'e
pattern is also observed by scanning tunneling spectroscopy. These findings can
open a route towards the strain engineering of graphene/metal interfaces with
various moir\'e superlattices and tailored electronic properties for nanoscale
information coding.
