Behavior and role of superficial oxygen in Cu for the growth of large single-crystalline graphene

- Growth mechanism of large graphene grains on oxidized Cu was revealed by investigating the behavior of oxygen in the Cu.
- Only the heating up step was found to be crucial for obtaining large graphene grains.
- The copper oxide layer was found to promote some oxygen atoms to dissolve into the Cu foil.
- The dissolved oxygen contributes to the reduction of a nucleation density of graphene.

Decreasing the nucleation density of graphene grown on copper (Cu) foil by chemical vapor deposition (CVD) is essential for the synthesis of large-area single-crystalline graphene. Here, the behavior of the copper oxide layer and its impact on the graphene growth have been investigated. We found that a small amount of oxygen dissolves into the Cu when the oxide layer decomposes during the heating up in a non-reducing Ar environment. The remaining oxygen in the Cu foil can play an important role in decreasing the graphene nucleation density. The dissolved oxygen can withstand at high temperatures even in reducing H2 environments without completely losing its effectiveness for maintaining a low graphene nucleation density. However, heating up in a H2 environment significantly reduces the copper oxide layer during the very first moments of the process at low temperatures, preventing the oxygen to dissolve into the Cu and significantly increasing the nucleation density. These findings will help to improve the graphene growth on Cu catalyst by increasing the grain size while decreasing the grain density.

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