First-principles study of mechanical, electronic and optical properties of Janus structure in transition metal dichalcogenides

Using first-principles calculations, we investigate mechanical, electronic and optical properties of so-called Janus structure for monolayer transition metal dichalcogenides (TMDs), MXY (M = Mo, W; X or Y = S, Se, Te; X not equal Y), in which chalcogen atoms at both side of the TMDs are not the same elements. Our calculated results indicate that WSSe shows the highest stiffness and the most ideal strength among the Janus TMDs due to their strongest ionic bond. In the unstrain cases, WSeTe, WSSe and MoSeTe are direct-gap semiconductors, while MoSSe, MoSTe and WSTe are indirect-gap semiconductors. The energy band gaps of the Janus TMDs decrease with increasing of the tensile strain due to the coupling between the p and d orbitals of the X/Y and M atoms, respectively. Furthermore, the tensile strain effectively modulates the optical absorption of the Janus TMDs. For example, the optical absorption of MoSSe is three times stronger at a photon energy of 2.5 eV. The calculated results of Janus TMDs provide useful information for applications in nanoelecromechanical, optoelectronic, and photocatalyst devices.