Using in-plane anisotropy to engineer Janus monolayers of rhenium dichalcogenides

TL;DR

This study explores how in-plane anisotropy in ReS₂ and ReSe₂ monolayers enables the creation of numerous Janus structures with tunable electronic and spin properties, expanding the potential for 2D material engineering.

Contribution

It introduces a method to engineer diverse Janus monolayers from in-plane anisotropic ReX₂ materials using first-principles calculations, highlighting their tunable electronic and spin characteristics.

Findings

Large number of stable Janus structures identified

Significant spin-orbit splitting and dipole moments observed

Work function can be tuned by chalcogen substitution

Abstract

The new class of Janus two-dimensional (2D) transition-metal dichalcogenides with two different interfaces are currently gaining increasing attention due to their distinct properties different from the typical 2D materials. Here, we show that in-plane anisotropy of a 2D atomic crystal, like ReS$_{2}$ or ReSe$_{2}$, allows formation of a large number of inequivalent Janus monolayers. We use first-principles calculations to investigate the structural stability of 29 distinct ReX$_{2-x}$Y$_{x}$ ($\mathrm{X,Y \in \{S,Se\}}$) structures, which can be obtained by selective exchange of exposed chalcogens in a ReX$_{2}$ monolayer. We also examine the electronic properties and work function of the most stable Janus monolayers and show that the large number of inequivalent structures provides a way to engineer spin-orbit splitting of the electronic bands. We find that the breaking of inversion symmetry leads to sizable spin splittings and spontaneous diople moments than are larger than those in other Janus dichalcogenides. Moreover, our caluclations suggest that the work function of the Janus monolayers can be tuned by varying the content of the substituting chalcogen. Our work demonstrates that in-plane anisotropy provides additional flexibility in sub-layer engineering of 2D atomic crystals.