Friction behavior of graphene edges within a carbon surface

We report the friction behavior of graphene edges within a carbon film, which encompasses structures ranging from amorphous carbon (a-C) to graphene nanocrystalline carbon (GNC). Structural characterization revealed that vertically growing graphene nanocrystallites were implanted into the a-C structure, exposing high-density layer edges on the film surface. Atomic force microscopy (AFM) nanofriction tests highlighted the nature of graphene edge friction. Firstly, the edge friction of GNC films was tested in a critical-contact state, and the results showed that graphene edges exhibited lower friction forces than did a-C edges. Secondly, the surface friction of GNC films was investigated in 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 behavior was attributed to the number of edges of the graphene nanocrystallites, which provided plentiful sp² C dangling bonds with weak bonding interactions and edge quantum wells with low surface potentials for lowering friction. These findings shed light on the importance of graphene-related materials and their high-density edges in the structural design and nanofriction application of carbon films.