Ripples, Wrinkles, and Crumples in Folded Graphene

Separation of two-dimensional thin-film-materials into single layers had been considered very challenging both theoretically and experimentally until the mechanical exfoliation method was discovered. After the successful separation of single- and/or few-layer graphene, the possibility of wrinkle formation has been one of the main open topics because they were not readily observed in experiments. Here, we report experimental observations of different kinds of repetitive nanoscale deformations (ripples, wrinkles, and crumples) in folded single-layer graphene (SLG) on an SiO(2)substrate. Using high-vacuum atomic force microscopy, we observed that SLG that was pre-transferred onto an SiO(2)substrate was accidentally folded multiple times during the tip-scanning, resulting in the formation of bilayer and trilayer graphene (TLG). Through high-resolution tapping-mode scanning, we could observe the wrinkles, ripples, and crumples in TLG. Additionally, we observed a herringbone pattern that was attributed to an intermediate stage between the wrinkles and ripples; this intermediate state was labeled as wrinklon structure. In our analysis, to characterize the ripples, wrinkles, and crumples, we measured the spatial repetition and amplitude of each pattern using their average line profile and compared them.