Structural studies of Ni-doped MoS₂ monolayers and polytypes using density functional theory

The crystal structure of MoS₂ gives rise to interesting properties for applications such as solid lubricants, optoelectronics, and catalysis. Transition-metal doping has been shown to enhance performance in solid lubrication and catalysis. We study the structure and properties of Ni-doped MoS₂ in the 1H and 1T monolayer and 2H and 3R bulk polytypes, using density functional theory. The doping formation energy for intercalation/adsorption shows that the most favorable sites are tetrahedral intercalation in bulk phases, Mo-atop in 1H and hollow site in 1T. We find the possibility of phase change from 2H to 3R with Mo or S substitution; also, Mo substitution induces metallic behavior in 3R and 2H, and both Mo and S substitution induce in-gap states in 1H, which could have interesting optoelectronic applications. Doping the 1T phase resulted in reconstructions leading to a metal-semiconductor transition. We find that Ni doping strengthens the layer binding which can explain the mechanism of low wear. This work gives insight into the previously unclear structure of Ni-doped MoS₂, the relation of energy and structures of doped monolayers and bulk systems, the electronic properties under doping, and the effect of doping on interlayer interactions. (arxiv: 2008.04301)