▎ 摘　　要

Because of the inconsistent observations, the Cu catalytic decomposition of methane for gaphene synthesis is reexamined, i.e., via the surface absorption, decomposition-to atomic carbon, and segregation. Here, we experimentally show the quantity of ambient Cu vapor is the key factor in graphene synthesis, which influences the dropwise condensations for airborne Cu clusters during growth. The masive carburization in Cu clusters and the calculation of carbon solubility in nanosized clusters are performed, experimented, and further examined from the growth of diamond-like-carbon films and ball-like diamonds via Cu vapor assisted growth on SiO2. The affinitive interactions between Cu vapor, ambient gases, and solid surface are embodied. By combining the molecular dynamics for the redeposited Cu clusters to surface, the vehicle theory of Cu clusters, which transports the atomic carbon to the surface and completes the graphene growth, is thus proposed as the essential puzzle we considered.