Scanning Tunneling Microscope Observations of Non-AB Stacking of Graphene on Ni Films

Microscopic features of graphene segregated on Ni films prior to chemical transfer--including atomic structures of monolayers and bilayers, Moire patterns due to non-AB stacking, as well as wrinkles and ripples caused by strain effects-have been characterized in detail by high-resolution scanning tunneling microscopy （STM）. We found that the stacking geometry of the bilayer graphene usually deviates from the traditional Bernal stacking （or so-called AB stacking）, resulting in the formation of a variety of Moir6 patterns. The relative rotations inside the bilayer were then qualitatively deduced from the relationship between Moir6 patterns and carbon lattices. Moreover, we found that typical defects such as wrinkles and ripples tend to evolve around multi-step boundaries of Ni, thus reflecting strong perturbations from substrate corrugations. These investigations of the morphology and the mechanism of formation of wrinkles and ripples are fundamental topics in graphene research. This work is expected to contribute to the exploration of electronic and transport properties of wrinkles and ripples.