Preparation and electronic structure of the WSe2/graphene/NiSex/Ni(111) heterostructure

In this work, a stacked heterostructure made up of single-layer WSe2 and graphene was created through a scalable and efficient way. Graphene was grown on a Ni (111) single crystal, producing an ordered and well-defined carbon overlayer that is strongly hybridized with the support, disrupting its peculiar conductive properties. A monolayer WSe2 was deposited on top of graphene by the simultaneous evaporation of metal W and elemental Se. We demonstrate here that the chalcogen can efficiently intercalate between graphene and the Ni surface, decoupling the two materials and forming a buffering NiSex layer. The concurrent selenization of both W and Ni effectively eliminates the need for an additional decoupling step in the synthesis of a free-standing graphene/Ni heterostructure. The formation process of the complex WSe2/Graphene/NiSex/Ni(111) heterostructure was studied by means of low-energy electron diffraction, x-ray photoelectron spectroscopy, angle-resolved ultraviolet photoelectron spectroscopy, and ex situ Raman spectroscopy. These analyses confirm the presence of single-layer WSe2 on top of a free-standing graphene.