Selecting "Convenient Observers" to Probe the Atomic Structure of Epitaxial Graphene Grown on Ir(111) via Photoelectron Diffraction

TL;DR

This paper uses photoelectron diffraction to precisely determine the atomic structure and corrugation of graphene grown on Ir(111), leveraging selective probing of surface states to overcome structural complexity.

Contribution

It introduces a novel approach using Ir 4f photoemission surface states as probes for atomic structure analysis of epitaxial graphene on Ir(111).

Findings

Measured average graphene height as 3.40 Å.

Determined graphene corrugation as 0.45 Å.

Validated simplified models for supercell analysis.

Abstract

Epitaxial graphene grown on metallic substrates presents, in several cases, a long-range periodic structure due to a lattice mismatch between the graphene and the substrate. For instance, graphene grown on Ir(111), displays a corrugated supercell with distinct adsorption sites due to a variation of its local electronic structure. This type of surface reconstruction represents a challenging problem for a detailed atomic surface structure determination for experimental and theoretical techniques. In this work, we revisited the surface structure determination of graphene on Ir(111) by using the unique advantage of surface and chemical selectivity of synchrotron-based photoelectron diffraction. We take advantage of the Ir 4f photoemission surface state and use its diffraction signal as a probe to investigate the atomic arrangement of the graphene topping layer. We determine the average height and the overall corrugation of the graphene layer, which are respectively equal to 3.40 $\pm 0.11 \AA$ and 0.45 $\pm 0.03 \AA$. Furthermore, we explore the graphene topography in the vicinity of its high-symmetry adsorption sites and show that the experimental data can be described by three reduced systems simplifying the Moir\'{e} supercell multiple scattering analysis.