Adsorption of water vaporby defect-free monolayers of d-transition metal dichalcogenides

Abstract

Two-dimensional nanomaterials are of great interest to researchers due to their exceptional mechanical and electronic properties, as well as the possibility of using them as gas sensors. To date, the mechanisms of water vapor adsorption upon contact of graphene-like monolayers of d-transition metal dichalcogenides with ambient air have not been practically studied. Therefore, in this work, theoretical studies of the adsorption of isolated water molecules by defect-free monolayers MoSe₂, WSe₂ , ReS₂ are carried out. Such characteristics as adsorption energy, the equilibrium distance of the water molecule to the surface of the monolayers, the density of electronic states, and the band gap are calculated. The calculations were carried out using the first principle method using the pseudopotential software package Quantum Espresso, based on the theory of the density functional theory. To carry out the calculations a supercell was built the dimensions of which made it possible to neglect the interaction of neighboring water molecules. For MoSe₂, WSe₂, the center of the hexagon, the metal atom, the selenium atom, and the middle of the metal-selenium bond are considered as potential adsorption centers. In the case of ReS₂, all nonequivalent atoms entering the unit cell are selected as potential adsorption centers. In the calculations, the positions of all atoms relaxed. It is shown that the water molecule is physically adsorbed on the defect-free surfaces of the monolayers considered. Adsorption of water molecules does not lead to a change in the electronic structure of monolayers and bandgaps, which excludes the possibility of using defect-free monolayers MoSe₂, WSe₂, ReS₂ as humidity sensors.