Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have layered structures with excellent tribological properties. Since the energy difference between hexagonal-molybdenum ditelluride (2H-MoTe₂) and distorted octahedral-molybdenum ditelluride (1T′-MoTe₂) is very small among the transition metal dichalcogenides (TMDCs), MoTe₂ becomes one of the most promising candidates for phase engineering. In our experiment, we found that the friction force and friction coefficient (COF) of 2H-MoTe₂ were an order of magnitude smaller than those of 1T′-MoTe₂ by the atomic force microscope (AFM) experiments. The friction difference between 1T′-MoTe₂ and 2H-MoTe₂ was further verified in molecular dynamics (MD) simulations. The density functional theory (DFT) calculations suggest that the friction contrast is related to the difference in sliding energy barrier of the potential energy surface (PES) for a tip sliding across the surface. The PES obtained from the DFT calculation indicates that the maximum energy barrier and the minimum energy path (MEP) energy barrier of 2H-MoTe₂ are both smaller than those of 1T′-MoTe₂, which means that less energy needs to be dissipated during the sliding process. The difference in energy barrier of the PES could be ascribed to its larger interlayer spacing and weaker Mo–Te interatomic interactions within the layers of 2H-MoTe₂ than those of 1T′-MoTe₂. The obvious friction difference between 1T′-MoTe₂ and 2H-MoTe₂ not only provides a new non-destructive means to detect the phase transition by the AFM, but also provides a possibility to tune friction by controlling the phase transition, which has the potential to be applied in extreme environments such as space lubrication.

Superlubricity and active friction control have been extensively researched in order to reduce the consumption of fossil energy, the failure of moving parts, and the waste of materials. The vibration-induced superlubricity (VIS) presents a promising solution for friction reduction since it does not require high-standard environment. However, the mechanism underlying the VIS remains unclear since the atomic-scale information in a buried interface is unavailable to experimental methods. In this paper, the mechanism of VIS was examined via numerical calculation based on the Prandtl–Tomlinson (PT) model and molecular dynamics (MD) simulations. The results revealed that the pushing effect of stick–slip is one of the direct sources of friction reduction ability under vibrational excitation, which was affected by the response amplitude, frequency, and the trace of the tip. Moreover, the proportion of this pushing effect could be modulated by changing the phase difference when applying coupled vibrational excitation in x- and z-axis. This results in a significant change in friction reduction ability with phase. By this way, active friction control from the stick–slip to superlubricity can be achieved conveniently.