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

TL;DR

This study uses surface x-ray diffraction to precisely characterize the nanorippling and undulation of a graphene monolayer on Ir(111), revealing phase-aligned ripples with small amplitude differences.

Contribution

It provides the first detailed in situ measurements of nanorippling and undulation in graphene/Ir(111), distinguishing effects of roughness from moiré-induced rippling.

Findings

Graphene nanorippling amplitude: 0.379 Å

Iridium top layer undulation: 0.017 Å

Average graphene-Ir distance: 3.38 Å

Abstract

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{\'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 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 (\(0.379 \pm 0.044\) \AA) than, {\it e.g.}, for the topmost Ir layer (\(0.017 \pm 0.002\) \AA). The average graphene-Ir distance is found to be \(3.38 \pm 0.04\) \AA.