▎ 摘　　要

To obtain a large-area single-crystal graphene, chemical vapor deposition (CVD) growth on Cu is considered the most promising. Recently, the surface oxygen on Cu has been found to suppress the nucleation of graphene. However, the effect of oxygen in the vapor phase was not elucidated sufficiently. Here, we investigate the effect of O-2 partial pressure (P-O2) on the CVD growth of graphene using radiation-mode optical microscopy. The nucleation density of graphene decreases monotonically with P-O2, while its growth rate reaches a maximum at a certain pressure. Our results indicate that P-O2 is an important parameter to optimize in the CVD growth of graphene. (C) 2015 The Japan Society of Applied Physics