Not yet reviewed by Pith; the record is open.

Copper foil impurities are hampering scalable production of high-quality graphene by chemical vapor deposition (CVD). Here, we conduct a thorough study on the origin of these unavoidable contaminations at the surface of copper after the CVD process. We identify two distinct origins for the impurities. The first type is intrinsic impurities, originating from the manufacturing process of the copper foils, already present at the surface before any high-temperature treatment, or buried into the bulk of copper foils. The buried impurities diffuse towards the copper surface during high-temperature treatment and precipitate. The second source is external: silica contamination arising from the quartz tube that also precipitate on copper. The problem of the extrinsic silica contamination is readily solved upon using an adequate confinement the copper foil samples. The intrinsic impurities are much more difficult to remove since they appear spread in the whole foil. Nevertheless, electropolishing proves particularly efficient in drastically reducing the issue.