Layer-Dependent Binding of NH₃ on MoS₂

Two-dimensional transition metal nitrides (TMNs) are a new class of material that have shown great promise for use in electronic and optoelectronic devices due to their high conductivity and stability. However, the synthesis of these large-area thin films of TMNs is still not fully understood. Current studies have shown that exposing layered MoS₂ crystals to NH₃ causes the MoS₂ to rapidly convert to Mo₅N₆, but the mechanism by which this convergence happens is still unknown. Here, we apply first-principles computational density functional theory (DFT) to investigate the nature of binding of NH₃ on layered MoS₂, considering the role of defects and number of layers. Our calculations show that the molecule binds selectively to defects, with a layer-dependence of the binding energy that is consistent with measured reactivity only in the presence of defect complexes containing multiple sulfur vacancies. Overall, this study indicates that defects are necessary for the atomic substitution synthesis of TMNs.<br/><br/>This work was supported by the DOE Office of Science, Basic Energy Sciences under Award No DE-SC0023402.