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

Abstract

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 $(0.379\ifmmode\pm\else\textpm\fi{}0.044\phantom{\rule{0.16em}{0ex}}\text{\AA{}})$ than, e.g., for the topmost Ir layer $(0.017\ifmmode\pm\else\textpm\fi{}0.002\phantom{\rule{0.16em}{0ex}}\text{\AA{}})$. The average graphene-Ir distance is found to be $3.38\ifmmode\pm\else\textpm\fi{}0.04\phantom{\rule{0.16em}{0ex}}\text{\AA{}}$.