Moiré superlattices in strained graphene-gold hybrid nanostructures

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 moire superlattices, which generate secondary Dirac points in the local density of states. Conversely, the graphene covered gold regions undergo a polycrystalline → Au (111) phase transition upon annealing. Moreover, the nanoscale coexistence of moire superlattices with different moire periodicities has also been revealed. Several of these moire 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 moire pattern is also observed by scanning tunneling spectroscopy. These findings can open a route towards the strain engineering of graphene/metal interfaces with various moire superlattices and tailored electronic properties for nanoscale information coding.