Is Single Layer MoS2 Stable in the Air?

Molybdenum disulfide (MoS₂ ) 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, MoS₂ monolayers lack long-term stability in air. Here, a study is presented on the oxidation of MoS₂ monolayers based on density functional theory (DFT) calculations. The results suggest that single-layer MoS₂ 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 MoS₂ . 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 MoO₃ . This MoO₃ structure facilitates the spread of oxidation onto the surface, and the stress associated with the misfit between the MoS₂ and MoO₃ lattices may cause the experimentally observed cracking of MoS₂ flakes.

Effects of Water Intercalation and Tribochemistry on MoS2 Lubricity: An Ab Initio Molecular Dynamics Investigation

To date, no clear conclusion has been reached on the atomistic mechanisms that govern the observed decrease of lubricating capabilities of MoS₂ in humid environments. Based on ab initio molecular dynamic calculations, we show that intercalated water molecules hinder the sliding motion of both regular and defective layers considerably, with the velocities decaying exponentially with time. However, in the presence of an applied load and exposed edge terminations, water is rapidly removed from the interface and is adsorbed on the edges either in undissociated form or as OH/H fragments. These outcomes suggest that the interlayer slipperiness can be reduced by the presence of water even in the absence of any chemical oxidation. Our work could help to set up more dedicated experiments to further tackle a technologically relevant issue for the applications of MoS₂ -based lubricants.

Reversible wurtzite-tetragonal reconstruction in ZnO(1010) surfaces

Bistable surface: The reversible phase transition between wurtzite (WZ) and body-centered-tetragonal (BCT) lattice was activated in ZnO(1010) surfaces and directly imaged at atomic scale by using aberration-corrected electron microscopy. A nucleation-growth mechanism for the surface reconstruction is further proposed based on observations and calculations of the WZ-BCT domain boundary.

Large-area vapor-phase growth and characterization of MoS(2) atomic layers on a SiO(2) substrate

Atomic-layered MoS(2) is synthesized directly on SiO(2) substrates by a scalable chemical vapor deposition method. The large-scale synthesis of an atomic-layered semiconductor directly on a dielectric layer paves the way for many facile device fabrication possibilities, expanding the important family of useful mono- or few-layer materials that possess exceptional properties, such as graphene and hexagonal boron nitride (h-BN).