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

Abstract

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 A²_1g 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 A²_1g for MoS₂ at around 463 cm^–1 confirm the enhancement of the interlayer coupling