▎ 摘　　要

Experiments on graphene growth through chemical vapor deposition (CVD) involving methane (CH4) and hydrogen (H-2) gases reveal a complex shape evolution and a non-monotonic dependence on the partial pressure of H-2 (p(H2)). To explain these intriguing observations, we develop a microkinetic model for the stepwise decomposition of CH4 into mobile radicals and consider two possible mechanisms of attachment to graphene crystals: CH radicals to hydrogen-decorated edges of the crystals and C radicals to bare crystal edges. We derive an effective mass flux and an effective kinetic coefficient, both of which depend on p(H2), and incorporate these into a phase field model. The model reproduces both the non-monotonic dependence on p(H2) and the characteristic shapes of graphene crystals observed in experiments. At small p(H2), growth is limited by the kinetics of attachment while at large p(H2) growth is limited because the effective mass flux is small. We also derive a simple analytical model that captures the non-monotone behavior, enables the two mechanisms of attachment to be distinguished and provides guidelines for CVD growth of defect-free 2D crystals.