Direct Visualization of Atomic-Scale Graphene Growth on Cu through Environmental Transmission Electron Microscopy.

The functionalities of two-dimensional (2D) materials are solely determined by their perfect single-layer lattice or precisely stacking of multiple lattice planes, which is predominately determined during their growth process. Although the growth of graphene has been successfully achieved on different substrates with a large area up to millimeters, direct visualization of atomic-scale graphene growth in real time still lacks, which is vital to decipher atomistic mechanisms of graphene growth. Here, we employ aberration-corrected environmental transmission electron microscopy (AC-ETEM) to visualize the nucleation and growth of graphene at the atomic scale in real time. We find a unique lateral epitaxial growth process of graphene on Cu edges under the CO atmosphere with a ledge-flow process. The nucleation of graphene nuclei from amorphous carbon atoms also has been found to proceed with a gradual ordering of in-plane carbon atoms. The coalescence of smaller graphene nanoislands to form large ones is thermodynamically favored, and the evolution of atomic structures at grain boundaries is also revealed in great details. These atomic insights obtained from real-time observations can provide direct evidence for the growth mechanisms of graphene, which can be extended to other 2D materials.