  The interlayer coupling in van der Waals heterostructures governs a variety
of optical and electronic properties. The intrinsic dipole moment of Janus
transition metal dichalcogenides (TMDs) offers a simple and versatile approach
to tune the interlayer interactions. In this work, we demonstrate how the van
der Waals interlayer coupling and charge transfer of Janus MoSSe/MoS2
heterobilayers can be tuned by the twist angle and interface composition.
Specifically, the Janus heterostructures with a sulfur/sulfur (S/S) interface
display stronger interlayer coupling than the heterostructures with a
selenium/sulfur (Se/S) interface as shown by the low-frequency Raman modes. The
differences in interlayer interactions are explained by the interlayer distance
computed by density-functional theory (DFT). More intriguingly, the built-in
electric field contributed by the charge density redistribution and interlayer
coupling also play important roles in the interfacial charge transfer. Namely,
the S/S and Se/S interfaces exhibit different levels of PL quenching of MoS2 A
exciton, suggesting the enhanced and reduced charge transfer at the S/S and
Se/S interface, respectively. Our work demonstrates how the asymmetry of Janus
TMDs can be used to tailor the interfacial interactions in van der Waals
heterostructures.
