Initial steps of oxidative etching of MoS 2 basal planeinduced by O 2

Abstract

We have investigated the first stages of oxidation of the basal plane of MoS2 with O2. The different intermediates in the energy landscape were found at 0 K with nudged-elastic band calculations, and their reactivity was evaluated at higher temperatures by performing ab initio molecular dynamics simulations. We identified the intermediates and mechanisms leading to the desorption of both SO and SO2 species. The key intermediate consists of an O atom bound on top of an S atom with a second O atom inserted into the S-Mo bond, giving rise to a stable O=S-O-Mo moiety. The mechanisms leading to this intermediate upon adsorption of O2 on the basal plane of MoS2 are discussed. From the O=S-O-Mo intermediate, SO2 may desorb directly generating a single sulfur vacancy on the surface while its decomposition leads to the desorption of SO and leaves substitutional oxygen on the surface. These etching mechanisms were also observed in the ab initio molecular dynamics simulations, in good agreement with energy profiles calculated along the reaction paths. Diffusion of O atoms on top of the sulfur layer and direct desorption of SO groups were never observed in the molecular dynamics simulations because these processes have high energy barriers (2.4 and 3.1 eV, respectively). However, subsurface diffusion of O atoms, involving the formation of both O-S and O-Mo bonds, is a competing process with lower energy barriers.