▎ 摘　　要

A new mechanism by which catalytic chemical vapor deposition of graphene spontaneously terminates at a single layer on Pt foils is discussed. This self-limited growth regime is identified by direct imaging of adlayer graphene evolution using in-situ environmental scanning electron microscopy. Two fundamentally different mechanisms for adlayer nucleation are revealed. Besides primary nucleation, which is the standard nucleation that occurs only at the onset of growth, a secondary nucleation of adlayers is observed near full coverage of the substrate. Direct observation reveals layer-dependent growth kinetics and the establishment of a dynamic equilibrium between the forward reaction of carbon incorporation and the reverse reaction of graphene etching. Increasing coverage of the active catalyst gives rise to a spontaneous reversal of adlayer evolution from growth to etching. The growth reversal has important practical benefits. It creates a self-limited growth regime in which all adlayer graphene is removed and it enables large-scale production of 100% single-layer graphene.