Air stability of monolayer WSiN in dark and bright conditions.

Two-dimensional materials with chemical formula MAZ 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 (O, HO, and CO) on monolayer WSiN, an established representative of the MAZ 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. O and water introduce localized states in the upper valence region but do not alter the semiconducting nature of WSiN 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 O chemisorption when negative charge carriers are in the system. In this case, monolayer WSiN 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 WSiN against HO and CO in both dark and bright conditions, suggesting the potential of this material in nanodevice applications.