Nanotribology of SiP nanosheets: Effect of thickness and sliding velocity

Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups. As a typical 2D group IV–V material, SiP has been widely used in photodetection and photocatalysis due to its high carrier mobility, appropriate bandgap, high thermal stability, and low interlayer cleavage energy. However, its adhesion and friction properties have not been extensively grasped. Here, large-size and high-quality SiP crystals were obtained by using the flux method. SiP nanosheets were prepared by using mechanical exfoliation. The layer-dependent and velocity-dependent nanotribological properties of SiP nanosheets were systematically investigated. The results indicate the friction force of SiP nanosheets decreases with the increase in layer number and reaches saturation after five layers. The coefficient of friction of multilayer SiP is 0.018. The mean friction force, frictional vibrations, and the friction strengthening effect can be affected by sliding velocity. Specially, the mean friction force increases with the logarithm of sliding velocity at nm/s scale, which is dominated by atomic stick-slip. The influence of frequency on frictional vibration is greater than speed due to the different influences on the change in contact quality. The friction strengthening saturation distance increases with the increase in speed for thick SiP nanosheets. These results provide an approach for manipulating the nanofriction properties of SiP and serve as a theoretical basis for the application of SiP in solid lubrication and microelectromechanical systems.