Characterizing zinc and zinc‑containing compounds using X‑ray photoelectron spectroscopy is often challenging, largely because the Zn 2p3/2 binding energies for different species show only subtle variations. A recently published study offers an extensive collection of reference spectra for metallic zinc and a wide range of zinc compounds. This work includes Zn 2p3/2 binding energy data and line shape information but also discusses the importance of the Zn LMM Auger signal and accompanying counter‑ion photoelectron signals [1]. Several related important analytical tools are also discussed, including the modified Auger parameter and chemical‑state (Wagner) diagrams, which may help distinguish between zinc chemical environments.
Figure 1 and Table 1 summarize reported literature positions for the Zn 2p3/2 peak, presenting mean values as well as their associated standard deviations. Although the Zn 2p3/2 signal is free from complications such as multiplet splitting, chemical analysis remains challenging due to significant signal overlap among different compounds. The situation is further complicated by factors such as natural line widths, variations in peak shapes, and the uncertainties introduced during charge referencing, all of which make reliable chemical‑state interpretation increasingly difficult.
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| Figure 1. Graphical summary of the average Zn 2p3/2 binding energies, along with their standard deviations, as reported in the published literature (Table 1). Note that this representation does not convey any information regarding peak widths. Figure adapted from reference [1]. |
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| Table 1. Average Zn 2p3/2 binding energies, Zn L3M4,5M4,5 kinetic energies, and corresponding standard deviations for several zinc species obtained from published literature. The number of references considered is also indicated (#). Table reproduced from [1]. |
Experimental data (Figure 2 and Table 2) reported in [1] show similar trends to those reported in the literature, confirming that the Zn 2p3/2 core line alone is often insufficient for reliably distinguishing between different zinc species. The publication highlights several possible complications, including peak asymmetry and the stability of certain compounds under X‑ray exposure. Regarding peak shape, most compounds analyzed in the study were found to exhibit some degree of asymmetry in their photoelectron line shapes. The best fits were obtained using either Lorentzian–asymmetric (LA) and Doniach–Šunjić (DS) line shapes as defined in CasaXPS. Stability concerns were also noted. Compounds such as Zn(OH)2 were found to undergo X‑ray‑induced degradation, indicating that precautions should be used, particularly minimizing collection time. An excellent summary of the X‑ray‑induced conversion of Zn(OH)2 to ZnO has been provided by Duchoslav et al. [2].
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Figure 2. Zn 2p3/2 core-level spectra for various zinc compounds considered in this study. For reference, vertical lines indicating the approximate binding energy of metallic zinc are overlaid in each panel. [1]
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| Table 2. Summary of experimentally measured Zn 2p3/2 binding energies, their FWHM, as well as their respective standard deviations. The approximate line shapes according to the LA and DS line shapes in CasaXPS are indicated. Please note that FWHM values reported here were made according to the LA line shape; only subtle variations occur when switching to the DS line shape (typically < 0.1 eV). [1] |
Compared with the Zn 2p3/2 core line, the Zn LMM Auger transition spans a broader kinetic-energy range, making it more effective for accurate zinc speciation, particularly when used in conjunction with the modified Auger parameter (Figure 3 and Table 3). In mixed systems containing multiple zinc species, both the position and the line shape of the Zn LMM Auger signal can provide valuable information for distinguishing among species. Table 4 summarizes the fitting parameters required to reproduce representative LMM line shapes, enabling reliable modelling of complex experimental envelopes. One potential complication when using the Zn LMM Auger transition is the presence of sodium, as the Na KLL Auger peak overlaps with the Zn LMM region. However, strategies for overcoming these challenges are also described in [1].
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| Figure 3. Wagner (chemical state) plot of Zn 2p3/2–Zn L3M4,5M4,5 transitions for the zinc compounds examined in this study. Data points from this work are shown as solid symbols, while selected literature values are represented as outlined symbols. Where available, literature averages are shown with corresponding standard deviations. [1] |
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| Table 3. Summary of experimentally measured Zn L3M4,5M4,5 kinetic energies, modified Auger parameter (α’), as well as their respective standard deviations. [1] |
A thorough interpretation of XPS data involving zinc and its compounds should draw on all available information, including the survey spectrum (for stoichiometry), the Zn 2p3/2 core line, the Zn LMM Auger transition, and the spectra of any associated counterions (see [1]). For systems containing multiple zinc compounds, the position and line shape of the Zn LMM transition often provide a more reliable means of speciation than the Zn 2p3/2 core line alone.
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| Table 4. Zn L3M4,5M4,5 curve fitting parameters. Each component is characterised by the same FWHM value, given in the final column. All components described here use the GL(30) line shape as described in CasaXPS. [1] |
References:
[1] J.D. Henderson, S.D.C. Buchanan, L.H. Grey, M.C. Biesinger,
Appl. Surf. Sci.,
730 (2026) 166284.
[2] J. Duchoslav, R. Steinberger, M. Arndt, D. Stifter,
Corros. Sci. 82 (2014) 356-361.
