Comparing both plots in Figure , we can see that the first flake appears after 4 min of exposure to methane, then the number of flakes increases. At time τ = 9 min, the densest packing of the flake assembly is observed while the flakes' size is the order of a few hundred μm. Then due to the strong interactions between the flakes leading to their coalescence, they begin to move, opening up the copper surface at τ = 20-23 min. The center of the sample (part under the beam) is entirely covered by graphene after 27 min while there are still some empty areas closer to the sample edges (video Growth_1). (b) Quantitative analysis of the growth 1: average flake lateral size (red) and average center-tocenter distance between neighboring flakes (green) deduced by optical microscopy, timeevolution of the layer coverage under the microscope (grey) and under the X-ray beam, extracted from the image (a) (blue).