A first-principles prediction of novel Janus T′-RuXY (X/Y = S, Se, Te) monolayers: structural properties and electronic structures

Due to the breaking of the mirror symmetry, two-dimensional layered Janus materials possess many extraordinary mechanical and electronic properties that cannot exist in symmetric structures. In this paper, we propose and investigate the structural and electronic properties of Janus T′-RuXY (X/Y = S, Se, and Te) monolayers using the first-principles simulations. Our calculated results indicate that the T′-RuXY is found to be dynamically and mechanically stable through the phonon dispersion analysis and examination of elastic properties. The T′-RuXY exhibits high anisotropic elastic characteristics due to its in-plane anisotropic atomic structure. Besides, the vertical asymmetry of T′-RuXY leads to the appearance of a difference in the vacuum level between its two different surfaces. At the ground state, all three structures of the Janus T′-RuXY are semiconductors with indirect bandgaps. The bandgaps of T′-RuXY can be modulated by a biaxial strain. Particularly, the semiconductor-to-metal phase transitions are observed in all studied structures at a large compressive strain. Our calculation results not only provide important structural and electronic features of the Janus T′-RuXY monolayers but also show the prospect of their application in nanoelectromechanical devices.