Anisotropic graphene growth accompanied by step bunching on a dynamic copper surface.

We investigated the initial stage of chemical vapor deposition graphene growth on Cu film at low pressure, where Cu evaporation intensively occurs. Surface steps on the Cu surface were found to be the nucleation sites of graphene islands and to affect the subsequent growth. For the first time, we observed anisotropic graphene growth on the Cu surface accompanied by morphological changes, resulting in an arrayed graphene ribbon formation. The resultant surface morphology is attributed to step bunching during growth. Detailed analyses suggest that the graphene arrays, which were preferentially formed along the steps, served as partial shields of the Cu surface, preventing step-flow-like Cu atom diffusion and evaporation at the growth site. As a result, the growth locations acted as a pinning site of the step motion, leading to step bunching. Such selective growth by using surface morphology has the potential to control not only the nucleation site but also the geometry of graphene for tailoring graphene-based nanomaterials such as nanoribbons and quantum dots.