Dynamic Nanofriction of Graphene Oxide Induced by a Positively Biased Conductive AFM Tip

Abstract

Graphene oxide (GO) with properties of large-scale preparation and application is an attractive solid lubricant. Understanding the tribological properties of GO under an electric field is crucial for the application of GO as a lubricant in electromechanical devices. Here, nanofriction properties of GO was measured in real-time using atomic force microscopy (AFM) with a positively biased conductive tip. The nanofriction force between the AFM tip and GO decreased sharply in the initial few tens of scan cycles. Then, a gradual decrease in nanofriction force was observed. The nanofriction force leveled off as the scan cycles further increased. The significant decrease in nanofriction force resulted from the reduction of oxygen-containing functional groups during the scan of the positively biased tip, which also led to the drop of height in the scanned area. Also, biased voltages, relative humidity, scan velocities, and normal loads affected the reduction and thus the nanofriction force. The exhibited low nanofriction force of GO after reduction makes it become an economically viable coating with the potential to extend the lifetime of electromechanical systems.