Air stability of monolayer WSi2N4 in dark and bright conditions

Abstract

Abstract Two-dimensional materials with chemical formula MA2Z4 are a promising class of materials for optoelectronic applications. To exploit their potential, their stability with respect to air pollution has to be analyzed under different conditions. In a first-principle study based on density functional theory, we investigate the adsorption of three common environmental gas molecules (O2, H2O, and CO2) on monolayer WSi2N4, an established representative of the MA2Z4 family. The computed adsorption energies, charge transfer, and projected density of states of the polluted monolayer indicate a relatively weak interaction between substrate and molecules resulting in an ultrashort recovery time of the order of nanoseconds. O2 and water introduce localized states in the upper valence region but do not alter the semiconducting nature of WSi2N4 nor its band-gap size apart from a minor variation of a few tens of meV. Exploring the same scenario in the presence of photogenerated electrons and holes, we do not notice any substantial difference except for O2 chemisorption when negative charge carriers are in the system. In this case, monolayer WSi2N4 exhibits signs of irreversible oxidation, testified by an adsorption energy of -5.5 eV leading to an infinitely long recovery time, a rearrangement of the outermost atomic layer bonding with the pollutant, and n-doping of the system. Our results indicate stability of WSi2N4 against H2O and CO2 in both dark and bright conditions, suggesting the potential of this material in nanodevice applications.

Keywords

• Two-dimensional materials
• Density functional theory
• WSi2N4 monolayer
• Air stability
• Gas adsorption