Intensity modulation of the Shirley background of the Cr 3p spectra with photon energies around the Cr 2p edge

Abstract

The background in X-ray photoelectron spectroscopy data originates, partially, from inelastically scattered photoelectrons. In fact, the current theoretical methods for calculating the background intensity are based on electron energy losses. However, a critical part of the experimental signal, which is known as the Shirley background, cannot be described within the current formalisms. This suggests that the Shirley electrons are not associated with energy losses of photoelectrons and must originate from a different photoexcitation phenomenon with a cross section of its own.We propose a mechanism based on core channeling as the physical origin of the Shirley signal.

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

“…The choice of fitting function and background has been the subject of many studies over the past 50 years and the references therein. In this section, three different approaches to combining Gaussian and Lorentzian function for fitting XPS spectra are described.…”

Comment on “Intensity modulation of the Shirley background of the Cr3p spectra with photon energies around the Cr2p edge”, by A Herrera‐Gomez, D Cabrera‐German, A D Dutol et al, Surface Interface Anal, 2018;50:246‐252

“…We note that the Cr2p, Cr3p, and Cr3s spectra in Figures 1 and 2 of the paper by Herrera‐Gomez et al are asymmetric to the higher binding energy side, as is the O1s spectrum in their Figure 2, indicating the presence of sub‐peaks; the C1s spectrum is not shown. While the presence of the O1s spectrum clearly indicates the existence of an oxide, this possibility was not considered in their discussion of the Cr peaks.…”

“…The reason for this is evident: The background is removed before the component peak is separated into its sub‐peaks and, for closely overlapping sub‐peaks, this results in a single step‐shaped baseline, rather than one for each sub‐peak. Perhaps because Herrera‐Gomez et al do not consider sub‐peaks, no mention is made of this problem in their paper.…”

“…In their Figure 2, Herrera‐Gomez et al chose, as background endpoints for the Cr2p spin‐orbit doublet, a binding energy just below the onset of the Cr2p 3/2 component (~570 eV), and another just above the end of the Cr2p 1/2 component (~590 eV). Unfortunately, this gives rise to a space between Shirley background and the Cr 2p spectrum at ~580 eV, clearly visible in the figure, implying the existence of a peak at that binding energy.…”

“…In a recent paper, Herrera‐Gomez et al considered the use and validity of the Shirley background to describe the baseline of the Cr2s, 2p and 3p X‐ray photoemission spectra. They were particularly concerned with the proper modeling of the background, which is so necessary for peak quantitation.…”