Friction at a single layer graphene edge on graphite: Part 2 - Simulation study with molecular dynamics

Arash Khajeh¹, Zhe Chen², Seong H. Kim^2,* and Ashlie Martini^1,*

¹ Department of Mechanical Engineering, University of California Merced, 5200 N. Lake Road, Merced, CA 95343, USA

² Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA

Abstract
Graphite has been widely used as a solid lubricant for many years. Its 2D crystal structure enables superlubricity in certain ambient conditions, but this is only observed far from surface defects like step edges. Recent experiments (Part 1 of this presentation) performed on graphite at step edges revealed friction behavior that could not be explained by topography or the Ehrlich–Schwoebel barrier theory. It was hypothesized that the friction at the step edge depends on the chemical nature of the edge. To explore this, here, we developed a reactive molecular dynamics simulation of a graphite substrate and a sliding silica tip.  This model was used to investigate atomic scale phenomena that affect friction behavior, including edge termination. The findings of this research provide insight into the critical role of defects and surface chemistry in general on the friction of 2D materials.