Spectroscopic Signatures for Interlayer Coupling in MoS2–WSe2 van der Waals Stacking

Stacking of MoS2 and WSe2 monolayers is conducted by transferring triangular MoS2 monolayers on top of WSe2 monolayers, all grown by chemical vapor deposition (CVD). Raman spectroscopy and photoluminescence (PL) studies reveal that these mechanically stacked monolayers are not closely coupled, but after a thermal treatment at 300 °C, it is possible to produce van der Waals solids consisting of two interacting transition metal dichalcogenide (TMD) monolayers. The layer-number sensitive Raman out-of-plane mode A21g for WSe2 (309 cm–1) is found sensitive to the coupling between two TMD monolayers. The presence of interlayer excitonic emissions and the changes in other intrinsic Raman modes such as E″ for MoS2 at 286 cm–1 and A21g for MoS2 at around 463 cm–1 confirm the enhancement of the interlayer coupling.