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

Periodic moiré 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 moiré 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° or 60° WS₂/MoSe₂ heterostructures, while the out-of-plane mode of MoSe₂ is only significantly decreased in near 0° heterostructures. Combining the intensity of out-of-plane Raman mode of WS₂ and MoSe₂, near 0° and 60° heterostructures can be distinguished without the need for complex optical characterizations. These typical peaks offer researchers an efficient way to construct the desired moiré superlattice structures.