Topography of the graphene/Ir(111) moiré studied by surface x-ray diffraction

The structure of a graphene monolayer on Ir(111) has been investigated in situ in the growth chamber by surface x-ray diffraction including the specular rod, which allows disentangling the effect of the sample roughness from that of the nanorippling of graphene and iridium along the moir\'e-like pattern between graphene and Ir(111). Accordingly, we are able to provide precise estimates of the undulation associated with this nanorippling, which is small in this weakly interacting graphene-metal system and thus has proved difficult to assess in the past. The nanoripplings of graphene and iridium are found in phase, i.e., the in-plane positions of their height maxima coincide, but the amplitude of the height modulation is much larger for graphene (0.379±0.0440.16em0ex) than, e.g., for the topmost Ir layer (0.017±0.0020.16em0ex). The average graphene-Ir distance is found to be 3.38±0.040.16em0ex.