Optical-assistant characterization of friction anisotropy properties of single-crystal graphene domains

Recently, large-area high-quality single-crystal graphene domains have been be fabricated using modified chemical vapor deposition (CVD). These hexagonal graphene domains have edges of zigzag chirality and micrometer size, which makes it possible to study the friction anisotropy properties caused by lattice orientations with multi-scale method. In this paper, an optical-assistant characterization method is first put forward. With the micro-scale optical system, the spatial relationship between the hexagonal graphene domain and the probe of the atomic force microscopy (AFM) was determined and changed gradually. Then a series of atomic-scale friction experiments were conducted under ambient conditions utilizing AFM lateral mode. During the process, the probe scanned along various lattice orientations with sample rotation method, which gets ride of the probe's anisotropic effect caused by the cantilever and the tip. And the stick-slip behaviors of the probe during this process were observed and recorded precisely. The scanning experimental results unveiled that the patterns of the stick-slip behaviors varied along different lattice orientation, which is caused by the distribution of graphene surface potential. The comparison between theoretical and experimental results shows that these variations can be regarded as the origin of the friction anisotropy on the graphene domains. The achievements will not only provide an effective method for the identification of lattice orientation, but also lay a more solid experimental base for multiscale research on graphene. The presented work can also provide a standard process for studies on various properties of graphene depended on lattice distribution.