Effect of stainless-steel substrate grain boundaries on surface graphene morphology and nano-friction behavior

The characteristics of graphene's surface morphology and frictional behavior can be significantly impacted by the underlying substrate material, particularly in the domain of nanofriction. This study observed that the grain boundaries present in polycrystalline substrates like stainless steel induce bulging in graphene, which, in turn, impacts its nanofriction behavior. While graphene exhibits low friction when tightly adsorbed on stainless steel grains, the phenomenon of graphene bulging leads to an increase in frictional force. Additionally, this study revealed that the process of contact between the tip and the bulging graphene gives rise to a two-stage frictional rise, wherein the rate of frictional rise and the underlying mechanism differs between the stages. The first stage of the frictional rise was explained using the fold theory, considering the contact area as the reference quantity. Using the tip atomic force statistics as a reference quantity, the second stage of frictional rise can be explained by quality evolution theory. Through a combination of experimental observations and theoretical analyses, this study provides a comprehensive understanding of the nano frictional behavior exhibited by graphene on stainless-steel substrates. The mechanism of action of the entire process of frictional changes caused by graphene bulging is revealed.