▎ 摘　　要

In situ scanning electron microscopy (SEM) was used for observing the nucleation of graphene by segregation of bulk-dissolved carbon on a flat polycrystalline nickel surface. Preferential nucleation sites were determined on large (1 1 1) grains. In combination with ex situ atomic force microscopy measurements at the same area as with SEM, the nucleation sites were found to have step-bunched structures. Possible nucleation mechanisms are discussed based on the difference in the carbon concentration and critical nucleus size between the (1 1 1) terrace and step bunches.