Selecting ‘convenient observers’ to probe the atomic structure of CVD graphene on Ir(111) via photoelectron diffraction

Abstract

CVD 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 ± 0.11 Å and 0.45 ± 0.03 Å. 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 moiré supercell multiple scattering analysis.

Evidencing the formation of Pt nano-islands on Cr2O3/Ag(111)

“…XPD experiments were carried out in the anglescanned mode, where the variation in the θ polar angle was applied in steps of 3°from 18°to 72°, while the azimuthal angle (∅) was varied in 3°steps from 0°to 120°. 41…”

X-ray photoelectron diffraction study of the approximant Al5Co2(001) quasicrystal

“…As a measure of the quality of the R -factor, the uncertainties can be calculated using the steepness of the R -factor space assigned to a parameter in the vicinity of its absolute minimum and the maximum number of separable diffraction information N with experimental data:with Var( R min ) being the variance of R at the minimum. 12–21 This way of calculating uncertainty was used by Van Hove et al (1993). 22…”

“…The photoemission intensities from different polar and azimuthal angles are normalized by the function χ , presented in the form of an anisotropy, given by:where I ( θ , φ , k⃑ ) is the measured or calculated photoemission intensity over all angles φ for a given angle θ , representing the background in the experiment and I 0 ( θ , φ , k⃑ ) is the photoelectron intensity in the absence of diffraction (free atoms). 12–22…”

“…The closer to zero R a is in better agreement with the experimental one. [12][13][14][15][16][17][18][19][20][21] As a measure of the quality of the R-factor, the uncertainties can be calculated using the steepness of the R-factor space assigned to a parameter in the vicinity of its absolute minimum and the maximum number of separable diffraction information N with experimental data:…”

“…with Var(R min ) being the variance of R at the minimum. [12][13][14][15][16][17][18][19][20][21] This way of calculating uncertainty was used by Van Hove et al…”