Predicting X-ray Photoelectron Peak Shapes: the Effect of Electronic Structure

Abstract

X-ray photoelectron spectroscopy (XPS) is a widely used tool for quantitative analysis of surfaces, providing critical information about elemental composition and the chemical state(s) of each element. Quantitative analysis of XPS data requires fitting of curves corresponding to different chemical states with appropriate spectral lines. Traditionally, analysis of peak profiles is performed using peak shapes that have been determined empirically; however, these methods cannot readily account for changes in the symmetry of peak shapes due to differences in electronic structure. A physically rigorous technique is introduced herein that can fit symmetric and asymmetric peak profiles by determining the Wertheim− Walker profile based on densities of states calculated by density functional theory (DFT + WW). The DFT + WW method uniquely can accurately predict changes in XPS line shape due to changes in d-band filling, lattice contraction and expansion, and atomically precise chemical environments. A DFT + WW profile is suitable for applications where a hypothesized model structure of a material can be accurately calculated and, in these cases, the XPS fits provide a test of whether the hypothesized structure has a similar density of states to the experimental sample. This could allow improved peak assignment and improved interpretation of XP spectra. When applied to spectra from single-crystal transition-metal samples, the DFT + WW method gives excellent fits, with a similar accuracy to common peak profilesVoigt, Doniach−S ̌unjic, and Mahan. Furthermore, the DFT + WW method captures experimentally observed changes in the peak shape between bulk metals and overlayer structures. Overall, the DFT + WW method provides a clear link between electronic structure and XPS line profile, allowing for possible improvements in the interpretation of XP spectra.

Corrosion inhibition in acidic environments: key interfacial insights with photoelectron spectroscopy

“…7(c)). As highlighted in another recent study, 30 we suggest that proper selection of model line shape functions will become increasingly important moving forward, as system complexity increases, e.g. , in near ambient pressure XPS studies, multiple components are commonly required to fit an XPS core level spectrum.…”

“…7(b)) of carbon steel immersed in either 1MHCl/OMID or 0.01MH 2 SO 4 /OMID, they are far from identical. For the latter, constraining each GL (30) function to have the same FWHM (i.e. $1.5 eV), six components were required to achieve a satisfactory t to the experimental data.…”

Metal nanoparticle-decorated germanane for selective photocatalytic aerobic oxidation of benzyl alcohol

“… 38 Pt 4f was deconvoluted into the Pt 4f 7/2 and 4f 5/2 spin–orbit couple and the energy separation of these doublets was fixed at 3.35 eV and the Pt 4f 7/2 to 4f 5/2 area ratio was fixed at 0.75. 39 …”

“…38 Pt 4f was deconvoluted into the Pt 4f 7/2 and 4f 5/2 spin-orbit couple and the energy separation of these doublets was fixed at 3.35 eV and the Pt 4f 7/2 to 4f 5/2 area ratio was fixed at 0.75. 39 Powder X-ray Diffraction (XRD) Analysis. XRD was performed using on a Bruker D8 Advance diffractometer (Cu-K α1 (λ = 1.5406 Å) and K α2 (λ = 1.5444 Å) radiation).…”

Metal Nanoparticle-Decorated Germanane for Selective Photocatalytic Aerobic Oxidation of Benzyl Alcohol

“…36 Pt 4f was deconvoluted into the Pt 4f7/2 and 4f5/2 spin-orbit couple and the energy separation of these doublets was fixed at 3.35 eV and the Pt 4f7/2 to 4f5/2 area ratio was fixed at 0.75. 37 Powder X-ray Diffraction (XRD) Analysis. XRD was performed using on a Bruker D8 Advance diffractometer (Cu-Kα1 (λ = 1.5406 Å) and Kα2 (λ = 1.5444 Å) radiation).…”