Spontaneous Closing of Torn Bilayer Graphene Edges via a Self-Healing Mechanism

The electronic transport properties of nanoscale patterned graphene are significantly influenced by its edge structures. Herein, we report a self-healing phenomenon of freshly torn bilayer graphene edges based on <i>in situ</i> scanning tunneling microscopy observations. The fresh bilayer edges are created in the surface graphene layers by tip-induced field evaporation. Surprisingly, atomic resolution images reveal the spontaneous formation of a half-tubular structure that seamlessly connects the upper and lower layers, identical to the edge of a folded monolayer graphene. It is attributed to a self-healing mechanism of open bilayer edges in aligned zigzag (or armchair) direction, where the transient edge carbon radicals evolve into sp² hybridized C-C bonds between neighboring layers. For armchair edges, the original AB stacking can be locked into the AA stacking due to required sliding of carbon atoms. This finding opens up an atomic precision edge engineering method of patterned graphene for devices.