Crystallinity dependent tribological behavior of molybdenum disulfide: Insights from experiments and atomistic simulations

The frictional and wear performance of molybdenum disulfide (MoS 2 ) is strongly governed by its crystallinity, yet this influence remains largely unexplored. In this study, we present the first integrated experimental and atomistic study that establishes how structural order governs the tribological performance of MoS 2 . A wide spectrum of crystallinity, from amorphous to highly crystalline states, is investigated to evaluate its influence on the coefficient of friction (COF) and wear resistance. Experiments reveal a strong dependence of COF and wear on crystallinity, with crystalline MoS 2 achieving ultralow friction and enhanced wear resistance. In contrast, amorphous and polycrystalline films display significantly higher COF and pronounced tribo-polishing effect. Complementary reactive molecular dynamics simulations capture the same trend and uncover the underlying mechanics: crystalline MoS 2 maintains smooth sliding interfaces and enables frictional anisotropy through interlayer shear. However, sliding of disordered structures increases surface roughness, energy dissipation, and material removal. Furthermore, we examine the wear mechanisms under high normal loads, demonstrating that crystallinity enhances wear resistance by mitigating material deformation. The strong agreement between experiments and simulations confirms crystallinity as a dominant factor governing the tribological response of MoS 2 . Our findings provide atomic-scale insights into the mechanisms of superlubricity in layered materials and offer a fundamental basis for designing advanced solid lubricants and wear-resistant coatings.