a, Top and profile view of the supercell of graphene, hydrogens and Cu(111). b, Theoretical simulation of bonding status for recombined hydrogen with H:C = 1:4 and 1:2 at 650 °C. Some of the hydrogen atoms form into H2 and increase their surface distance. c, AFM image of graphene grown on Cu(111) substrate (region 30 μm × 30 μm). Wrinkles are not apparent. d, Enlarged AFM image (5 μm × 5 μm). Wrinkles can be recognized by adjusting the height scale. e, Height profiles extracted from d. The wrinkles are usually lower than 1 nm. The root-mean-square (RMS) roughness is about 0.756 nm for c and 0.538 nm for d. Scale bars in c, d are 10 μm and 1 μm, respectively.