Modeling sputtering deposition of MoS2: Effect of Ni doping on nanostructure and tribological properties

The nanostructure and tribological properties of molybdenum disulfide (MoS${}_2$) doped with nickel (Ni) were investigated using reactive molecular dynamics simulations. Sputtering deposition simulations captured the formation of MoS${}_2$ films with different Ni concentrations (0%, 2%, 10%, and 15% by weight) and temperatures (300 K and 670 K). The morphology of the deposited films was characterized in terms of density, crystallinity, and Ni clustering. The deposited films were then compressed and sheared in simulations designed to mimic the function of the material as a dry film lubricant. Results showed that, in these simulations, the 2% and 10% Ni-doped films exhibited lower shear stress than the 0% and 15% Ni-doped films. This non-monotonic trend was analyzed in terms of the evolution of the film nanostructure during shear. It was found that the films that exhibited low shear stress formed a lubricious particle, characterized by a crystalline core and amorphous, Ni-containing surface. The lubricious particle was formed through a combination of density, crystallinity, and Ni clustering conditions only possible with the intermediate amount of Ni. The findings suggest that optimizing the Ni concentration during sputtering may be a promising approach to improve the tribological performance of MoS${}_2$ dry film lubricants.