The use and misuse of curve fitting in the analysis of core X‐ray photoelectron spectroscopic data

Abstract

Core X-ray photoelectron spectroscopic (XPS) data often contain overlapping chemically shifted peaks that differ in their width, peak shape, and intensity. The spectra may be complicated by the presence of satellite and multiplet splitting features as well as from the X-ray satellites that arise when achromatic X-radiation is used. Curve fitting has been extensively used for more than the past 50 years as a means of extracting chemical information from the overlapping features in core XPS. Our understanding of the key components of this approach, such as the fitting function and the spectral background, has improved substantially over the years.XPS is now the most widely used surface analytical method, and many users often have their principal expertise in other areas. While the associated computer software in most XPS instruments has powerful data analysis techniques, including curve fitting, provided by the manufacturer or by a separate commercial source, the application of these techniques may not always be appropriately applied. This perspective article gives the author's view of the main issues that impact the use of curve fitting, together with a description of some approaches that misuse curve fitting leading to erroneous conclusions about the surface chemistry. The article is illustrated by examples showing the fitting of various types of spectra using true Voigt functions.

Selective, High-Temperature O2 Adsorption in Chemically Reduced, Redox-Active Iron-Pyrazolate Metal–Organic Frameworks

“…For this material, we observe an O 1s signal that we accordingly assign to oxygen-containing defect species at a binding energy of 531.1 eV (Figure 4), consistent with hydroxides or oxygencontaining organics such as formate. [37][38][39][40][41][42] This peak is also observed at a similar binding energy in K1.06Fe2(bdp)3, as well as in both O2-dosed K1.06Fe2(bdp)3 samples. Critically, for both of these O2-dosed samples, a new O 1s peak is also present at a higher binding energy of ~534.1 eV, consistent with a superoxo, rather than more reduced peroxo or oxo species.…”

Practical guide for x-ray photoelectron spectroscopy: Applications to the study of catalysts

“…Such complexity poses real challenges to even the most experienced analysts and one must always be on guard against commonly encountered errors such as incorrectly attributing peak asymmetry, satellite structure, multiplet splitting or screened photoemission peaks to non-stoichiometric or high oxidation states (see for example [59][60][61][62][63][64][65][66] ). An excellent paper on the use and misuse of curve fitting is given by Sherwood 67 , and we highlight some of the points raised in that paper in the following sections.…”

Ultrathin tunable conducting oxide films for near-IR applications: an introduction to spectroscopy shape theory

“…XPS spectra are also complicated by the presence of X-ray satellites and ghosts, so it is necessary to adjust the curves to extract the chemical information from these data. Although the XPS instrument software includes curve fitting, its misuse leads to erroneous conclusions about surface chemistry [14]. We present a novel spectroscopy analysis based on shape theory ( [15] and related works) and cumulative XPS data [16].…”