Suppressing graphene nucleation during CVD on polycrystalline Cu by controlling the carbon content of the support foils

The oxidative carbon removal from Cu foils was systematically studied together with the resulting suppression of the graphene flake nucleation during subsequent chemical vapor deposition (CVD). The carbon content was determined by segregating bulk dissolved carbon during a special rapid cooling process towards the surface, where it was detected by x-ray photoelectron spectroscopy. After exposure to a standardized hydrogen pretreatment, the Cu foils deliver irregularly distributed CVD grown flakes with diameters of 0.1-20 μm. Such foils still contain 40-240 monolayers of carbon, which could be removed by exposure to an oxygen partial pressure of ∼10−5 mbar diluted in 1 mbar Ar carrier gas. This controlled procedure allowed the quantification of the carbon removal while inducing exclusively reversible restructuring of the Cu foil. Only when lowering the carbon content to values well below 1 monolayer per entire Cu foil, the flake nucleation during CVD drops to values below 1 flake/mm2. We also show that it is the absence of carbon and not the presence of oxygen which accounts for the low flake density and that graphene can be grown with up to mm sized domains. Our data question many proposed explanations why certain growth protocols deliver graphene of comparable high quality.