Interaction of oxygen molecules with MoS2 monolayers

Abstract

Transition-metal dichalcogenides (TMDs) form a versatile class of two- dimensional semiconductors whose properties can be engineered more directly than those of graphene. Among them, monolayer 2H–MoS2 stands out: the indirect gap in the bulk becomes direct in the monolayer, which is very promising for electronic and optoelectronic device applications, while the large surface/volume ratio also enhances reactivity to temperature, pressure, and oxygen. In this context, we investigate pristine monolayer MoS2 and the thermodynamics of oxygen incorporation in the TMD matrix, in particular, substitution on sulfur sites, and quantify the resulting modifications to the electronic structure. Moreover, the thermodynamics of MoS2 oxidation remain unresolved; therefore, mapping this reaction is the main objective of this work. Calculations are carried out within density functional theory (DFT). Spin–orbit coupling (SOC) is included to resolve spin-splitting in both valence and conduction bands. It is readily noted that the incorporation of oxygen into MoS2 matrix leads to significant electronic modifications. Defect formation energies are obtained by combining DFT total energies with temperature- and pressure-dependent chemical potential corrections. This procedure enables us to explore and understand the favorability of oxygen incorporation in MoS2 in different environmental conditions. The calculations were performed in ideal conditions (T= 0K) and at experimental conditions where temperature and pressure effects were considered. It can be observed that the formation energy diagrams are in good agreement with the experimental results. Moreover, the barriers for sulfur-vacancy passivation were calculated in two different paths, as well as the thermal stability of the oxygen-substituted MoS2 in the dilute regime.