van der Waals trilayers and superlattices: modification of electronic structures of MoS2 by intercalation

Abstract

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 a 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 a transition-metal dichalcogenide (TMDC) MoSe₂ or WSe₂ sheet makes the sandwich trilayer undergo 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 to the MoS₂/TMDC/MoS₂ trilayer heterostructures, albeit a slight decrease of the bandgap compared to 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.