Topography of the graphene/Ir(111) moir{é} studied by surface x-ray diffraction

The structure of a graphene monolayer on Ir(111) has been investigated {\it 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{é}-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 proved difficult to assess in the past. The nanoripplings of graphene and iridium are found in phase, i.e. the in-plane position of their height maxima coincide, but the amplitude of the height modulation is much larger for graphene ($0.379 \pm 0.044$ Å) than, {\it e.g.}, for the topmost Ir layer ($0.017 \pm 0.002$ Å). The average graphene-Ir distance is found to be $3.38 \pm 0.04$ Å.

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