Friction of a single layer graphene edge on graphite: Part 1 - Experimental study with atomic force microscopy 

Zhe Chen¹, Arash Khajeh², Ashlie Martini^2,* and Seong H. Kim^1,*

¹ Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA

² Department of Mechanical Engineering, University of California Merced, 5200 N. Lake Road, Merced, CA 95343, USA

Abstract
Graphene is considered to be an excellent coating for lubrication. However, graphene edges, which are nearly inevitable on graphene coatings, have a significant effect on the friction properties of the coating. In this work, the friction properties of a single layer graphene edge on highly oriented pyrolytic graphite (HOPG) are investigated with atomic force microscopy (AFM). The friction force between a Si tip and the graphene surface is recorded as the tip slides across the graphene edges. Unprecedented phenomena on the friction, which cannot be simply explained by Ehrlich–Schwoebel barrier theory, are discovered. It is assumed that the friction of the graphene edge is not only associated with the topography, but also dependent on the chemical condition of the edge. Further analysis of these phenomena is performed with molecular dynamics simulation (Part 2 of this presentation). This work enriches the understanding of frictional properties at atomic step edges and is helpful for the application of 2D materials as lubricant coating.