Self-assembled metallic nanoparticle superlattices on large-area graphene thin films: growth and evanescent waveguiding properties

We report a facile fabrication method for copper nanoparticle superlattices, based on thermal evaporation of ultrathin layers of copper on solution-processed thin films formed by few-layer graphene platelets. We show that the annealing of these systems in nitrogen without previous exposure to air prompts the heterogeneous nucleation of the Cu layer into nanoparticle superlattices self-assembled along specific crystallographic directions of graphene. Theoretical calculations suggest a lowest formation energy for Cu-nanoparticle arrays aligning along armchair directions, indicating that their self-assembly is energetically more favourable. The possibility of using these superlattices in evanescent waveguiding devices is explored by three-dimensional scanning near-field optical microscopy. The light-confining properties of our systems in the near-field indicate that our nanoparticle superlattices are poised to satisfy the technological demands required by nanophotonics devices.