Bending deformation and self-restoration of submicron-sized graphite cantilevers

Van der Waals (vdW)-stacked materials exhibit unique mechanical properties owing to their strong in-plane atomic bonds and weak interlayer vdW interactions. In this study, we experimentally demonstrate that submicron-sized graphite cantilevers can accommodate large out-of-plane deformations without fracturing and undergo self-restoration upon unloading. Submicron-sized cantilever beam specimens were fabricated from highly oriented pyrolytic graphite using the focused ion beam method and subjected to in situ transmission electron microscopy-based bending tests. The cantilevers exhibited a nonlinear load–displacement relationship, and their deformation was almost completely restored upon unloading, even though a large hysteresis loop was observed during the loading–unloading process. Moreover, similar loading–unloading curves were obtained during the repeated loading of the same specimen, indicating that the mechanical properties were restored by unloading even in the case of large nonlinear deformations. For larger deformations, plastic deformation occurred, and the self-restoration property was lost. However, no clear fracture was observed in the cantilevers even when they were deformed to a deflection angle of 62°. Even in this case, the deformation could be restored by electron-beam irradiation. Based on the obtained results, we propose a mechanism to explain the nonlinear and fully reversible deformation behavior of the specimens.