Exploring oxygen in graphene chemical vapor deposition synthesis

Graphene's practical applications require its reproducible production with controlled means. In particular, graphene synthesis by chemical vapor deposition on metals has been shown to be a promising way to produce large-size and high-quality graphene film at low cost. Understanding the reaction mechanisms during the synthesis process is vital for process and product controllability. There have been a great deal of studies regarding the mutual interplays between the metal, graphene, and hydrogen in graphene production, leading to significant advances in controllable graphene synthesis. Recently, oxygen has been found to play a key role in each step of graphene synthesis, especially on Cu. Taking oxygen into consideration, one can explain the divergent experimental results under similar conditions reported before and can grasp it as another powerful tool that can help to regulate the synthesis processes. The primary discoveries of the function of oxygen in graphene synthesis are summarized and discussed herein, divided into four aspects, corresponding to the elementary steps in graphene synthesis. Oxygen may also further promote graphene synthesis toward the final goal of developing wafer-scale single crystals with definite layer numbers and defects.