Electronic band structure of Two-Dimensional WS2 /Graphene van der Waals Heterostructures

Combining single-layer two-dimensional semiconducting transition-metal dichalcogenides (TMDs) with a graphene layer in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single-layer $\mathrm{W}{\mathrm{S}}₂$ on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements, and density functional theory (DFT) calculations. The results show good electronic properties as well as a well-defined band arising from the strong splitting of the single-layer $\mathrm{W}{\mathrm{S}}₂$ valence band at the $K$ points, with a maximum splitting of 0.44 eV. By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is close to the calculations for suspended single-layer $\mathrm{W}{\mathrm{S}}₂$. Our results provide an important reference for future studies of electronic properties of $\mathrm{W}{\mathrm{S}}₂$ and its applications in valleytronic devices.