Interfacial coupling in rotational monolayer and bilayer graphene on Ru(0001) from first principles

The interaction of graphene with metal is of critical importance for further optimization of the growth and transfer processes to achieve productive graphene. Here we report first-principles calculations with van der Waals corrections to address in-plane orientation effects on the geometric structure and electronic properties of monolayer and bilayer graphene on a Ru(0001) surface. We find that the recently measured slight rotation between monolayer graphene and Ru lattices minorly affects the characteristic geometric and electronic structures simulated to date for strict alignment. For epitaxial bilayer graphene, we unveil that a 25°-twisted bilayer graphene commensurate with Ru reproduces at best the hallmarks of free-standing electron-doped monolayer graphene as measured experimentally. At variance the classical Bernal stacking manifests the strongest interlayer coupling by destroying the Dirac point and exhibiting a graphite-like STM appearance. Our theoretical findings question the definite nature of the interfacial coupling of successive graphene layers grown on a strongly interacting metal substrate.