Asymmetric Growth of Tetragon-Shaped Single-Crystalline Graphene Flakes on Copper Foil by Annealing Treatment under Oxygen-Free Conditions

Engineering graphene into a particular shape is vital for potential industrial applications. To this end, better understanding of the growth mechanism is needed to control the growth behavior of graphene on a substrate surface with a specific shape. In this work, a tetragon-shaped graphene single crystal (TS_GSC) with millimeter-scale grain size was achieved on copper foil, which was annealed at oxygen-free conditions (AOF) prior to graphene growth. The TS_GSC grains are featured by two dendritic Frontiers at the shorter-edge (SE) sides and two sharp Frontiers at the longer-edge (LE) sides of graphene grain. By combining scanning electron microscopy, optical microscopy, and Raman mapping with carbon isotope labeling, we revealed for the first time an asymmetric growth behavior of TS_GSC grains on an AOF-treated copper substrate. It was supposed that the growth of graphene was determined by the diffusion limited aggregation mechanism at the SE side, whereas it was governed by the edge-determined atom-attachment mechanism at the LE side of graphene grain. In addition to single-layer graphene, tetragon-shaped bilayered graphene with grain size over 200 pm was also achieved on the AOF-treated copper substrate.