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.

中文翻译：

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折叠石墨烯中的波纹、皱纹和皱褶

在发现机械剥离方法之前，将二维薄膜材料分离成单层在理论上和实验上都被认为是非常具有挑战性的。在成功分离单层和/或少层石墨烯后，皱纹形成的可能性一直是主要的开放主题之一，因为在实验中不容易观察到它们。在这里，我们报告了对 SiO 2 衬底上折叠单层石墨烯 (SLG) 中不同类型的重复纳米级变形（波纹、皱纹和皱褶）的实验观察。使用高真空原子力显微镜，我们观察到预先转移到 SiO 2 衬底上的 SLG 在尖端扫描过程中意外折叠多次，导致双层和三层石墨烯 (TLG) 的形成。通过高分辨率敲击模式扫描，我们可以观察到 TLG 中的皱纹、波纹和皱褶。此外，我们观察到人字形图案，这归因于皱纹和波纹之间的中间阶段；这种中间状态被标记为皱纹结构。在我们的分析中，为了表征波纹、皱纹和皱褶，我们使用它们的平均线轮廓测量了每个图案的空间重复和幅度，并进行了比较。