Sulfur Structures on Bare and Graphene-Covered Ir(111)

Abstract

We present a study of sulfur adsorption on bare Ir(111). Two well-defined superstructures are found: a and a c(4 × 2) S-adlayer. Moreover, we also investigate sulfur intercalation of graphene on Ir(111). For adsorption, sulfur is provided either in the form of the precursor molecule H2S or as elemental sulfur through sublimation from FeS2 heated in a Knudsen cell. On the basis of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), as well as density functional theory calculations (DFT), we present a model for the c(4 × 2) superstructure consistent with surface relaxations. We show that above a graphene coverage threshold, when islands of the two-dimensional (2D) material start to coalesce, the sulfur superstructure intercalated below graphene depends on the form in which sulfur is provided: c(4 × 2) forms in the case of exposure to elemental sulfur, while the superstructure forms in the case of H2S exposure. The two intercalation structures influence the graphene moiré corrugation in different ways. We have used DFT calculations to determine sulfur adsorption energies, surface relaxations, and the influence of sulfur intercalation on the density of electronic states of graphene on Ir(111).

Growth Mechanism and Thermal Stability of a MoS2–Graphene Interface: A High-Resolution Core-Level Photoelectron Spectroscopy Study

“…A LEED pattern was acquired at the end of the S uptake, and it confirmed the c(4 × 2) ordering (see the Supporting Information). This and the XPS analysis we performed are in line with the surface model proposed by Pielićet al 46 The formation of highly ordered structures in this experiment indicates a strong interaction between sulfur and the Ir(111) substrate, which could interfere with the MoS 2 growth by hindering some sulfur atoms from bonding to molybdenum atoms on Gr.…”

“…This is accompanied by an adsorbate-induced rearrangement of the surface atoms with respect to the bare-surface situation, namely, the buckling of some surface atoms. In order to verify the compatibility of our outcomes with the results reported in the literature, we refer to earlier work indicating that the adsorbate-induced core-level shift of the clean surface component for a transition metal (TM) surface depends, in the first instance, both on the substrate geometry/symmetry and adsorption site. , Assuming that, in our experiment, the ( structure is responsible for the Ir 1 and S 1 components, we can deduce that the adsorption site of S for the high-coverage configuration related to the Ir 2 component whose BE shift Δ E Ir 2 = 540 meV is compatible with the configuration having a threefold adsorption site with a double-sulfur coordination for the Ir atoms, which is the configuration that was indeed identified and proposed for this interface . A more detailed analysis of this adsorption process is provided in the Supporting Information.…”

“…3) 30 × °ordered structure with only threefold fcc adsorption sites for Θ = 0.33 43−45 and a c(4 × 2) structure for Θ = 0.50 ML. 46 The latter structure displays S in hcp and fcc adsorption sites with half of the Ir surface atoms bonded to one S adatom and the other half bonded to two S adatoms. This is accompanied by an adsorbate-induced rearrangement of the surface atoms with respect to the bare-surface situation, namely, the buckling of some surface atoms.…”

“…3) 30 × °structure is responsible for the Ir 1 and S 1 components, we can deduce that the adsorption site of S for the high-coverage configuration related to the Ir 2 component whose BE shift ΔE Ir 2 = 540 meV is compatible with the configuration having a threefold adsorption site with a doublesulfur coordination for the Ir atoms, which is the configuration that was indeed identified and proposed for this interface. 46 A more detailed analysis of this adsorption process is provided in the Supporting Information.…”

“…It has been reported that sulfur adsorbed on Ir(111) forms a ( ordered structure with only threefold fcc adsorption sites for Θ = 0.33 − and a c(4 × 2) structure for Θ = 0.50 ML . The latter structure displays S in hcp and fcc adsorption sites with half of the Ir surface atoms bonded to one S adatom and the other half bonded to two S adatoms.…”