Atomic-Scale Superlubricity in TiCO@MoS Layered Heterojunctions Interface: A First Principles Calculation Study.

The two dimensional (2D)-layered transition-metal carbides and nitrides (MXene) have been proved to be an excellent solid lubricant owing to their high mechanical strength, low shearing strength, and self-lubricating properties. However, the interfacial friction behavior between Ti C ( = 1, 2) MXene and its heterogeneous system is not thoroughly exploited yet. Here, four types of van der Waals structures (TiCO@TiCO, TiCO@TiCO MoS@MoS, and TiCO@MoS) have been investigated by density functional theory (DFT) calculations. The results exhibit that TiCO@MoS possesses the lowest sliding energy barrier around 0.015 eV/oxygen(O) atom compared with the other three constructed models. Therefore, this work mainly focuses on the inner relation of TiCO@MoS interlayer friction behaviors and its attributing factors, including normal force and charge density. The DFT analysis shows that the roughness of the potential energy corrugated plane is positively correlated with normal force and predicted the ultralow friction coefficient (μ) at 0.09 when sliding along the minimum energy potential route. Moreover, friction coefficient fluctuates at the normal force less than 10 nN determined by the combined effect of interfacial charge interlock and redistribution. This work reveals the intrinsic connection between the friction and charge interaction at heterogeneous interfaces.