Influence of Interfacial Chemistry and Oxygen on Graphene Step Edges as Antiwear Coatings

Graphene has been widely applied to assemble antiwear coatings due to its ultrahigh mechanical strength and intrinsically lubricating properties; however, the ubiquitous atomic step edges as typical defects in coating are vulnerable to wear depending on the environment atmosphere. Here, we reported atomic attrition of the mechanically exfoliated graphene step edge and its silicon substrate against a Si probe initiating at a much lower threshold load in room air in comparison with peel-induced rupture as a dominant failure behavior at high loads in vacuum. Further investigations indicate that the atomic attrition of the graphene step edge should mainly originate from the interfacial chemical reactions with the chemically active Si probe associated with surrounding oxygen. Oxygen facilitates the atomic wear of graphene edges, whereas water molecules adsorbed at the step edge as a lubricating layer suppress edge damage. Even under oxygen conditions, only peel-induced rupture as a mechanical wear of the graphene edge was observed when scratched with an inert diamond probe. This study elucidates the two wear mechanisms operating at the graphene step edges and provides a strategy to enhance the wear resistance of graphene coatings by reducing ambient oxygen levels and minimizing interfacial chemical interactions.