Oxidative etching of S-vacancy defective MoS2 monolayer upon reaction with O2

The reactions of O-2 with S vacancy sites within a MoS2 monolayer were investigated using density functional theory calculations. We considered the following defects: single S vacancy, double S vacancy, two adjacent S vacancies and two S vacancies separated by a sulphur atom. We found that the surface distribution of S vacancy sites plays a key role in determining the surface reactivity towards O-2. We observed the desorption of SO2 only for the last vacancy distribution. For the other cases, the surface becomes passivated with very stable structures having O atoms on the original vacancy sites and in some cases an SO group in an adjacent position. The ab initio molecular dynamics simulations showed that the impingement of the O-2 molecule on an S vacancy site produces a stable chemisorbed O-2 molecule with an upright configuration. The surface reactions initiate after the O-2 molecule switches to the lying-down configuration which favours the breakage of the O-O bond and the concurrent formation of S-O bonds. In the most reactive vacancy site configuration, the dissociation of the first O-2 molecule produces an SO intermediate which finally leads to desorption of SO2 after oxygen abstraction from the other adjacent O-2 molecule. The formation of a MoO3 moiety within the monolayer was also observed in the molecular dynamic simulations at higher oxidation levels.

Automated summary

The study investigated the reactions of O-2 with S vacancy sites within a MoS2 monolayer through density functional theory calculations. It was found that the surface distribution of S vacancy sites plays a crucial role in determining the surface reactivity towards O-2, leading to different reaction outcomes depending on the defect distribution.