The graph in Figure also presents the analysis of the optical microscopy images recorded during growth 1 in parallel with the X-ray measurements. The corresponding video can be found in the SI (video Growth_1). We use MATLAB to extract the following parameters: the lateral size of the flakes (red), the center-to-center distances between the neighboring flakes (green), and the surface coverage with graphene in the field of view (grey). The area of the sample accessible with the optical microscope through the glass window is ~5.0×3.7 mm, which is much larger than the beam footprint. Therefore, this technique provides a larger data set.