Formation of graphene p-n superlattices on Pb quantum wedged islands

On the basis of first-principles calculations within density functional theory, we report on a novel scheme to create graphene p-n superlattices on Pb wedged islands with quantum stability. Pb(111) wedged islands grown on vicinal Si(111) extend over several Si steps, forming a wedged structure with atomically flat tops. The monolayer thickness variation due to the underlying substrate steps is a sizable fraction of the total thickness of the wedged islands and gives rise to a bilayer oscillation in the work function of Pb(111) due to quantum size effects. Here, we demonstrate that when a graphene sheet is placed on the surface of such a Pb wedged island, the spatial work function oscillation on the Pb wedged island surface caused by the underlying steps results in an oscillatory shift in the graphene Dirac point with respect to the Fermi level. Furthermore, by applying an external electric field of ∼0.5 V/Å in the surface normal direction, the Fermi level of the system can be globally tuned to an appropriate position such that the whole graphene layer becomes a graphene p-n superlattice of seamless junctions, with potentially exotic physical properties and intriguing applications in nanoelectronics.