LAUSR

The current-carrying nanofriction characteristics plays an important role in the performance, reliability, and lifetime of graphene-based micro/nano electromechanical systems and nanoelectronic devices. The atomic scale friction characteristics of graphene were investigated using conductive atomic force microscopy by applying positive-bias and negative-bias voltages. The atomic scale friction increased with applied voltages. Also, the friction under positive-bias voltages was lower than under negative-bias voltages, and the friction difference increased with the voltages. The different frictional behavior resulted from the inherent work function difference and the water molecules between tip and graphene. The applied voltages amplify the effect of work function difference on the friction, and the water molecules played different roles under negative-bias and positive-bias voltages. The friction increased rapidly with the continuous increase of negative-bias voltages due to the electrochemical oxidation of graphene. Nevertheless, the friction under positive-bias voltages remained low and the structure of graphene was unchanged. These experimental observations were further explained by modeling the atomic scale friction with a modified Prandtl-Tomlinson model. The model allowed determination of the basic potential barrier and voltage-induced potential barrier between tip and graphene. The calculation based on the model indicated the negative-bias voltages induced larger potential barrier than the positive-bias voltages. The studies suggest that graphene can achieve better lubricant performance by working as a lubricant coating for the cathode of the sliding electrical contact interfaces and provide a beneficial guideline for the applications of graphene in current-carrying friction.