Is Single Layer MoS 2 Stable in the Air?

Molybdenum disulfide (MoS 2 ) is extensively studied because of its potential applications in catalysis, electronic and optoelectronic devices, and composite nanostructures. However, a recent experimental study indicated that, contrary to current beliefs, MoS 2 monolayers lack long‐term stability in air. Here, a study is presented on the oxidation of MoS 2 monolayers based on density functional theory (DFT) calculations. The results suggest that single‐layer MoS 2 samples with exposed edge sites are indeed unstable to oxidation, which occurs because of the low energetic barrier to dissociation of oxygen molecules at the Mo‐edges of MoS 2 . After an oxygen molecule dissociates, oxygen atoms replace sulfur atoms, and further oxidation causes the formation of a one‐dimensional chain‐like structure resembling that of bulk MoO 3 . This MoO 3 structure facilitates the spread of oxidation onto the surface, and the stress associated with the misfit between the MoS 2 and MoO 3 lattices may cause the experimentally observed cracking of MoS 2 flakes.