New Insights into Gas-Solid Interactions of NO/MoS Monolayers: a Comparative Study with MoSe and MoTe Monolayers.

Understanding the microscopic electronic structure determines the macroscopic properties of the materials. Sufficient sampling has the same foundational importance in understanding the interactions. The NO/MoS interaction is well known, but there are still many inconsistencies in the basic data, and the source of the NO direct dissociation activity has not been revealed. Based on a large-scale sampling density functional theory (DFT) study, the optimal adsorption of the NO/MoS monolayer system is determined. The impurity state on the top of the valence band of the S-vacancy monolayer (MoS-V) was determined by cross-analysis of the band structure and density of states, which has been neglected for a long time. This provides a reasonable explanation for the direct dissociation of NO on the MoX monolayers. Further atomic structure analysis reveals that the impurity state originates from the not-fully occupied valence orbitals. This also corroborates the fact that the Mo material has dissociation activity, while the W material does not. There is no impurity state on the top of the valence band of the X-vacancy WS and WSe monolayers. Interestingly, NO dissociation did not occur in the MoTe-V monolayer. This may be related to the 6s inert electron pair effect of the Te atom. The double-oriented adsorption behavior of NOis also revealed. In contrast to the MoSe and MoTe monolayers, NO2-oriented adsorption on the MoS perfect monolayer deviates obviously, which is speculated to be related to space limitation and larger electronegativity of the S atom. The oriented adsorption ability of the MoX monolayers followed the order MoTe (64.4%) > MoSe (44.8%) > MoS (42.7%), according to the directed proportion. Renewed insights into the adsorption basic data and the understanding of the electronic structure of NO/MoX (X = S, Se, Te) monolayer systems provide a basic understanding of the gas-surface interactions and various future surface-related advanced applications.