Adhesion and nanotribological properties of folded graphene prepared by mechanical exfoliation

Atomic force microscope was used to study the adhesion of mechanical exfoliated graphene under two different atmosphere conditions, air and nitrogen. It was found that the adhesion under nitrogen was smaller. The adhesion of graphene edge was larger than that of the inner region. The relationship between the adhesion of folded graphene and the number of layers along with its frictional properties were investigated under nitrogen atmosphere. The results showed that the adhesion was independent of the number of folded graphene layers. The frictional properties of each area of the folded graphene were far beyond the SiO₂ substrate. The friction coefficients of the single layer, the fold on single layer, the double layers and the fold on double layers regions were successively decreased, which were 0.049, 0.031, 0.023 and 0.021 respectively. The friction forces were successively decreased as well. The frictional property of the folded graphene was weaker than the unfolded graphene of same number of layers due to the weaker bonding force between the layers. When measuring the adhesion with a sharp tip or a ball tip, the measurement history of adhesion had little influence on subsequent adhesion. Studies on freshly folded graphene in the air showed that the friction force of the folded region was significantly higher than that of the unfolded region.