Density functional theory investigations of PbSnX2 (X = S, Se, Te) monolayers: Structural and electronic properties

In asymmetrical Janus materials, the absence of the vertical mirror symmetry results in the extraordinary mechanical and electronic properties of these structures and has been studied by many scientists currently. In this work, based on the group-IV monochalcogenides MX (M = Pb, Sn, X = S, Se, Te), we study the structural, mechanical, and electronic properties of the Janus structures PbSnX2 by using the density functional theory. The obtained results indicate that PbSnX2 is dynamically stable and can be synthesized as free-standing monolayers by experiment. The difference in the calculated work function on the two sides of these monolayers is the result of the difference in vacuum levels between the surfaces originating from the asymmetry structure. It is also found that these three systems behave semiconductor properties with the band gaps can be modified under the effect of strain engineering. Interestingly, the band gap of the Janus PbSnTe2 reduces to zero when 10% compressive strain is applied. Our findings contribute significantly to the understanding of the physical properties of these Janus monolayers and guide material designs, especially, for nanoscale applications.