Interface between graphene and silicon of various surface planes.

Density functional theory has been employed to study graphene on silicon (Si) substrates of (111), (100) and (110) surface planes. There are several interesting findings. First, carbon atoms in graphene form covalent bonds with Si atoms, when placed close enough on Si (111) and (100) surfaces, whereas on (110) surface, the graphene plane remains unperturbed and recovers to the van der Waals distance to the Si surface. We then focus on two specific properties of graphene, work function and carrier density, which are key to a wide range of promising applications, such as graphene-Si solar cell and photodetector. The presence of a Si (111) surface shifts the Fermi level of graphene into its conduction band, resulting in an increase of the work function by 0.29 eV and of electron density by three orders of magnitude. The carrier density of graphene can also be increased by fifty times on Si (100), merely due to the modification of the density of states at the edge of bands without doping. These findings are related to the flexibility of the Si surface network, determined by the surface density of Si atoms. We should point out that this paper addresses possible impacts that various surface planes of a substrate can have on graphene and the physics behind. Applying the results to a real device of a specific plane requires further including surface reconstruction in bigger unit cells and environmental effects.