Spectroscopic Signatures of Interlayer Coupling in Janus MoSSe/MoS₂ Heterostructures

Engineering interlayer coupling through the twist angle or applied electric field has gained interest due to the breakthroughs of magic-angle graphene and twisted transition metal dichalcogenides (TMDs). The structural asymmetry of Janus TMD, in which the chalcogens are different on both sides, provides an inherent vertical electric field to tune the interlayer coupling. Here, we demonstrate the manipulation of phononic and excitonic properties of Janus MoSSe/MoS₂ heterostructures through changing the twist angle or reversing the electric field direction by forming S/S and Se/S interfaces. The MoSSe/MoS₂ heterostructure with the S/S interface displays higher interlayer phonon mode frequencies and stronger PL quenching of the intralayer exciton, suggesting a stronger interlayer coupling than the Se/S interface. First-principles calculations support the experiments and explain the interlayer coupling by the charge density redistribution and band hybridization. Our work paves the way for tailoring van der Waals interactions using Janus TMDs, which can facilitate the design of Moiré superlattices.