Surface Potential Variations in Graphene Induced by Nanostructured Crystalline Ionic Substrates

We used electrostatic force and Kelvin probe microscopies to investigate few-layer graphene (FLG) domains on top of ionic crystals. Step edges, pits, and protrusions within the ionic surface create sizeable and local perturbations of the surface potential of graphene overlayers. These were within the eV range in FLG with up to three layers, and become considerably screened in thicker layers. Engineering such nanostructures in a regular manner can allow the bottom-up creation of on-sheet p--n junctions and superlattices that exploit the Dirac nature of carriers in graphene, and provide a test bed for studying local screening.