Revealing the twist-angle-dependent interlayer coupling in WS2/MoSe2 heterostructures

Periodic moire superlattice structures in transition metal dichalcogenides (TMDs) heterostructures exhibit nanoscale tunable electronic and optical properties. Much effort has been devoted to understand the twist-angle-dependent optical properties of the TMDs heterostructures. Therefore, quickly determining the stacking angle of TMDs and constructing the desired moire superlattice structure is crucial. Here, we investigate the twist-angle-dependent optical properties of WS2/MoSe2, finding that the out-of-plane Raman mode is a reliable marker for determining the stacking angle. The interlayer exciton energy, being close to that of MoSe2 excitons, is highly sensitive to material quality and fabrication, making it unsuitable for identifying the stacking angle. In contrast, the out-of-plane Raman peaks of WS2 and MoSe2 are more sensitive to changes in the stacking angle. The out-of-plane Raman mode of WS2 is enhanced more than fivefold in near 0 degrees or 60 degrees WS2/MoSe2 heterostructures, while the out-of-plane mode of MoSe2 is only significantly decreased in near 0 degrees heterostructures. Combining the intensity of out-of-plane Raman mode of WS2 and MoSe2, near 0 degrees and 60 degrees heterostructures can be distinguished without the need for complex optical characterizations. These typical peaks offer researchers an efficient way to construct the desired moire superlattice structures.