Tuning the Electronic Structure of Monolayer Graphene/MoS2 van der Waals Heterostructures via Interlayer Twist

TL;DR

This study investigates how the electronic structure of monolayer graphene/MoS2 heterostructures is affected by twist angle, revealing that MoS2's electronic properties are twist-dependent while graphene's remain unchanged, enabling bandgap engineering.

Contribution

The paper provides direct experimental measurements of twist-angle effects on the electronic structure of monolayer graphene/MoS2 heterostructures, highlighting twist-dependent bandgap modifications.

Findings

Graphene's electronic structure remains unaffected by twist angle.

MoS2's valence band maximum energy difference varies with twist angle.

MoS2 becomes an indirect bandgap semiconductor outside 30-degree twist.

Abstract

We directly measure the electronic structure of twisted graphene/MoS2 van der Waals heterostructures, in which both graphene and MoS2 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 MoS2, the resulting band structure reveals the absence of hybridization between the graphene and MoS2 electronic states. Further, the graphene-derived electronic structure in the heterostructures remains intact, irrespective of the twist angle between the two materials. In contrast, however, the electronic structure associated with the MoS2 layer is found to be twist-angle dependent; in particular, the relative difference in the energy of the valence band maximum at {\Gamma} and K of the MoS2 layer varies from approximately 0 to 0.2 eV. Our results suggest that monolayer MoS2 within the heterostructure becomes predominantly an indirect bandgap system for all twist angles except in the proximity of 30 degrees. This result enables potential bandgap engineering in van der Waals heterostructures comprised of monolayer structures.