We directly measure the electronic structure of twisted graphene/$\mathrm{Mo}{\mathrm{S}}_2$ van der Waals heterostructures, in which both graphene and $\mathrm{Mo}{\mathrm{S}}_2$ are monolayers. We use cathode lens microscopy and microprobe angle-resolved photoemission spectroscopy measurements to image the surface, determine twist angle, and map the electronic structure of these artificial heterostructures. For monolayer graphene on monolayer $\mathrm{Mo}{\mathrm{S}}_2$, the resulting band structure reveals the absence of hybridization between the graphene and $\mathrm{Mo}{\mathrm{S}}_2$ electronic states. Further, the graphene-derived electronic structure in the heterostructures remains essentially intact, irrespective of the twist angle between the two materials. In contrast, however, the electronic structure associated with the $\mathrm{Mo}{\mathrm{S}}_2$ layer is found to be twist-angle dependent; in particular, the relative difference in the energy of the valence band maximum at $\overline{\mathrm{\Gamma }}$ and $\overline{K}$ of the $\mathrm{Mo}{\mathrm{S}}_2$ layer varies from approximately 0 to 0.2 eV. Our results suggest that monolayer $\mathrm{Mo}{\mathrm{S}}_2$ within the heterostructure becomes predominantly an indirect band-gap system for all twist angles except in the proximity of ${30}^{\circ }$. This result enables potential band-gap engineering in van der Waals heterostructures comprised of monolayer structures.

• Received 1 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.201409

Source: http://link.aps.org/doi/10.1103/PhysRevB.92.201409