Direct imaging of a single Ni atom cutting graphene to form a graphene nanomesh.

A large area graphene nanomesh (GNM) etched by Ni is synthesized by a facile one-step liquid arc discharge in a Ni-containing solution. Atomic-resolution scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS) is applied to identify the atomic structures of the product. The results show that the GNM with a pore size of about 10-50 nm comprises single- or few layer graphene, and there are some small pores of size 1 nm and defects of five membered rings or seven membered rings in the positions of the skeletons. Also Ni atoms or nanoparticles are uniformly distributed in graphene or at the edges of the GNM. A dynamic study using a microscope shows that the Ni atom at the edge of graphene is active and can move along the edge, which facilitates the fracture of C-C bonds and the diffusion of carbon atoms greatly. DFT calculation results show that the diffusion of carbon atoms along the edge in the GNM containing Ni is easier than that in pristine graphene. The Ni atoms or particles act as an "atomic knife" to cut the graphene sheet to feed the formation of the GNM. These results represent a significant advancement in the growth mechanism study of GNMs and thus the precise structure control of graphene.