Unraveling the Structural and Electronic Properties at the WSe2-Graphene Interface for a Rational Design of van der Waals Heterostructures

WSe2 thin films grown by chemical vapor deposition on graphene on SiC(0001) are investigated using photoelectron spectromicroscopy and electron diffraction. By tuning of the growth conditions, micrometer-sized single or multilayer WSe2 crystalline islands preferentially aligned with the main crystallographic directions of the substrate are obtained. Our experiments suggest that the WSe2 islands nucleate from defective WSex seeds embedded in the support. We explore the electronic properties of prototypical van der Waals heterostructures by performing id-angle resolved photoemission spectroscopy on WSe2 islands of varying thickness (mono- and bilayer) supported on single layer, bilayer, and trilayer graphene. The experiments are substantiated by DFT calculations indicating that the interaction between WSe2 and graphene is weak and the electronic properties of the resulting heterostructures are unaffected by the thickness of the supporting graphene layer or by the crystallographic orientation. Yet the WSe2 graphene distance and the WSe2/WSe2 interlayer separation strongly influence the electronic band alignment at the high symmetry points of the Brillouin zone. The values of technology relevant quantities such as splitting of spin polarized bands and effective mass of electrons at band valleys are extracted from experimental angle resolved spectra. These findings establish further strategies for tuning the morphology and electronic properties of artificially fabricated van der Waals heterostructures that may be used in the fields of nanoelectronics and valleytronics.