  We perform a comprehensive first-principles study of the electronic
properties of van der Waals (vdW) trilayers via intercalating a two-dimensional
(2D) monolayer (ML = BN, MoSe2, WS2, or WSe2) between MoS2 bilayer to form
various MoS2/ML/MoS2 sandwich trilayers. We find that the BN monolayer is the
most effective sheet to decouple the interlayer vdW coupling of the MoS2
bilayer, and the resulting sandwich trilayer can recover the electronic
structures of the MoS2 monolayer, particularly the direct-gap character.
Further study of the MoS2/BN superlattices confirms the effectiveness of the BN
monolayer for the decoupling of the MoS2-MoS2 interaction. In addition, the
intercalation of transition-metal dichalcogenide (TMDC) MoSe2 or WSe2 sheet
renders the sandwich trilayer undergoing an indirect-gap to direct-gap
transition due to the newly formed heterogeneous S/Se interfaces. In contrast,
the MoS2/WS2/MoS2 sandwich trilayer still retains the indirect-gap character of
the MoS2 bilayer due to the lack of the heterogeneous S/Se interfaces.
Moreover, the 3D superlattice of the MoS2/TMDC heterostructures also exhibits
similar electronic band characters as the MoS2/TMDC/MoS2 trilayer
heterostructures, albeit slight decrease of the bandgap than the trilayers.
Compared to the bulk MoS2, the 3D MoS2/TMDC superlattice can give rise to new
and distinctive properties. Our study offers not only new insights into
electronic properties of the vdW multilayer heterostructures but also guidance
in designing new heterostructures to modify electronic structures of 2D TMDC
crystals.
