▎ 摘　　要

We investigate the critical methane concentration (CMC) during the atmospheric-pressure chemical vapor deposition (AP-CVD) of graphene on Cu from CH4. Above the CMC, graphene both nucleates and grows; below the CMC, it etches; while at the CMC, carbon intermediate species attach and detach from graphene at equal rates. By studying how the CMC varies with [H-2] and temperature, we determine the reaction mechanism and the intermediates. We find that the CMC scales with [H-2](3/2) and determine a single Arrhenius temperature dependence close to the expected equilibrium value. For [CH4] > CMC, the radial growth rate is proportional to the " building unit" supersaturation indicating that graphene growth occurs under capture-limited kinetics through an intermediate hydrocarbon that is first-order dependent on [CH4] and proportional to [H-2](-3/2). We develop a CH4 decomposition and capture model which is consistent with all measurements indicating that the intermediate is CH. We find that uniform monolayer graphene can only be achieved in AP-CVD near the CMC, with a nucleation density that varies 5 orders of magnitude from 880 to 1075 degrees C. Thus, our work also provides a roadmap for growing uniform graphene at atmospheric pressure on Cu over a broad range of experimental conditions.