Gas Modulation Induced Ultra-Low Friction and Ultra-Strong Wear Resistance in Atomically Thin MoSe₂ Single Crystals

Atomically thin films exhibiting ultra-low friction and ultra-strong wear resistance are crucial for overcoming lubrication challenges in micro-nano electromechanical systems (M/NEMS). However, achieving these properties under conventional pressure conditions remains a major challenge. In this study, a novel strategy is presented to further reduce friction and enhance wear resistance by tuning the atmosphere composition. High-quality monolayer (ML, ≈0.9 nm) and bilayer (BL) MoSe₂ single crystals are successfully synthesized via the chemical vapor deposition (CVD) method. Compared to BL MoSe₂, ML MoSe₂ exhibits ultra-low coefficient of friction (COF = 0.0091) and super wear resistance (40 000 cycles@2.17 GPa) under atmospheric conditions. Additionally, the surface friction can be modulated by varying the oxygen-to-nitrogen ratio, and the best friction reduction and anti-wear properties are achieved in pure nitrogen. Notably, the COF of ML MoSe₂ can be further reduced by 50% (COF = 0.004), and the wear resistance increases nearly four times (208,640 cycles@2.26 GPa) in pure N₂. Experimental and molecular dynamics analyses reveal that stronger adhesion of N₂ molecules to the surface, coupled with weaker intermolecular interactions, promotes ultra-low friction and super wear-resistance in ML MoSe₂. The molecular mechanism proposed by this work provides a new degree of freedom for friction modulation and also introduces a promising strategy in constructing ultra-low friction and super wear-resistant systems with atomic-scale thickness.