Friction behaviour of graphene edges within carbon surface

Abstract

We reported a friction behaviour of graphene edges within carbon film, encompassing the structures ranged from amorphous carbon (a-C) to graphene nanocrystalline carbon (GNC). Structural characterization revealed that vertical-growing graphene nanocrystallites implanted into a-C structure, exposing high-density layer edges on the film surface. AFM nanofriction test highlighted the nature of graphene edge friction. Firstly, the edge friction of GNC films was tested at a critical-contact state, and the results showed that graphene edges exhibited lower friction forces compared to a-C edges. Secondly, the surface friction of GNC films was investigated at a full-contact state, revealing that the edge friction of graphene nanocrystallites regulated the surface friction of GNC films. As the edge density of graphene nanocrystallites increased, the nanofriction force of GNC films decreased. Finally, the mechanism of the regulated friction bahaviour was attributed to the amount of the edges of graphene nanocrystallites, which provided plentiful sp² C dangling-bonds with weak bonding interactions and edge quantum wells with low surface potentials for lowing the friction. This finding shed light on the significance of graphene-related materials and their high-density edges in the structural design and nanofriction application of carbon films.