Core level photoemission line shape selection: Atomic adsorbates on iron

Robust fitting of core level photoemission spectra is often central to reliable interpretation of X-ray photoelectron spectroscopy (XPS) data. One key element is employment of the correct line shape function for each spectral component. In this study, we consider this topic, focusing on XPS data from atomic adsorbates, namely, O and S, on Fe(110). The potential of employing density functional theory (DFT) for generating adsorbate projected electronic density of states (PDOS) to support line shape selection is explored. O 1s core level XPS spectra, acquired from various ordered overlayers of chemisorbed O, all display an equivalent asymmetric line shape. Previous work suggests that this asymmetry is a result of finite O PDOS in the vicinity of the Fermi level, allowing O 1s photoexcitation to induce a weighted continuum of final states through electron-hole pair excitation. This origin is corroborated by O DFT-PDOS generated for an optimised five-layer Fe(110)(2 × 2)-O slab. Adsorbate DFT-PDOS were also computed for Fe(110) (Formula presented.) -S. As, similar to adsorbed O, there is a significant continuous distribution of states about the Fermi level, it is proposed that the S 2p XPS core levels should also have asymmetric profiles. S 2p XPS data acquired from Fe(110) (Formula presented.) -S, and their subsequent fitting, verify this prediction, suggesting that DFT-PDOS could aid line shape selection.