  We propose an innovative, easy-to-implement approach to synthesize large-area
singlecrystalline graphene sheets by chemical vapor deposition on copper foil.
This method doubly takes advantage of residual oxygen present in the gas phase.
First, by slightly oxidizing the copper surface, we induce grain boundary
pinning in copper and, in consequence, the freezing of the thermal
recrystallization process. Subsequent reduction of copper under hydrogen
suddenly unlocks the delayed reconstruction, favoring the growth of
centimeter-sized copper (111) grains through the mechanism of abnormal grain
growth. Second, the oxidation of the copper surface also drastically reduces
the nucleation density of graphene. This oxidation/reduction sequence leads to
the synthesis of aligned millimeter-sized monolayer graphene domains in
epitaxial registry with copper (111). The as-grown graphene flakes are
demonstrated to be both single-crystalline and of high quality.
