The Transition of Friction Coefficient on Graphene by the Microsphere Probe

The friction properties of graphene at the microscale are important for its application as a solid lubricant in micro-/nano-electromechanical system components. In this work, the friction properties of graphene under the action of a 5-mu m-diameter microsphere probe are investigated using atomic force microscopy. A special phenomenon was found that the friction coefficient changed from positive to negative during the unloading process on different thicknesses of graphene. The applied normal load corresponding to the turning point of friction coefficient was not subject to the variation of the unloading range but increased with the increment of graphene thickness. Different stick-slip behaviors were observed, demonstrating the main reason for the above frictional characteristics is out-of-plane deformation. The anomalous friction between the contact interface of the microsphere probe and the graphene discussed broadens new horizons for the frictional properties of graphene.

Automated summary

In this study, the friction properties of graphene as a solid lubricant in micro-/nano-electromechanical system components were investigated using atomic force microscopy. It was found that the friction coefficient of graphene changed from positive to negative during the unloading process on different thicknesses of graphene. The turning point of friction coefficient was not affected by the unloading range but increased with the thickness of graphene. Different stick-slip behaviors were observed, indicating that the out-of-plane deformation of graphene is the main reason for these frictional characteristics. The anomalous friction at the contact interface between the microsphere probe and graphene expands the understanding of the frictional properties of graphene.