Topographic and electronic contrast of the graphene moir\'e on Ir(111) probed by scanning tunneling microscopy and non-contact atomic force microscopy

TL;DR

This study combines STM and AFM techniques to distinguish between electronic and topographic contrasts in the graphene moiré pattern on Ir(111), revealing true surface topography and atomic-scale corrugation details.

Contribution

It demonstrates how AFM can accurately measure the true surface topography of graphene on Ir(111), separating it from electronic effects seen in STM images.

Findings

Moiré corrugation of 35±10 pm observed.

Graphene-Ir distance varies with atomic site, smallest atop iridium atoms.

AFM provides true topography, unlike STM which is influenced by electronic states.

Abstract

Epitaxial graphene grown on transition metal surfaces typically exhibits a moir\'e pattern due to the lattice mismatch between graphene and the underlying metal surface. We use both scanning tunneling microscopy (STM) and atomic force microscopy (AFM) experiments to probe the electronic and topographic contrast of the graphene moir\'e on the Ir(111) surface. While STM topography is influenced by the local density of states close to the Fermi energy and the local tunneling barrier height, AFM is capable of yielding the 'true' surface topography once the background force arising from the van der Waals (vdW) interaction between the tip and the substrate is taken into account. We observe a moir\'e corrugation of 35$\pm$10 pm, where the graphene-Ir(111) distance is the smallest in the areas where the graphene honeycomb is atop the underlying iridium atoms and larger on the fcc or hcp threefold hollow sites.