This paper addresses the challenges of fitting asymmetric photoelectron peaks by showing that the use of the double Lorentzian (DL) line shape usually leads to high-quality, reliable, and reproducible fits. In contrast to the Doniach-Sunjic (DS) line shape, used to fit asymmetric peaks, the DL distribution is integrable and produces higher-quality fits. The functional form of the DL is described in detail; examples of the application of the DS line shape to fit transition metals and one transition metal oxide are shown. The transition from symmetric Voigt functions, used to fit many photoelectron peaks, to asymmetric DL functions is smooth and easy. The DL is encompassed in the freely available AAnalyzer software (https://xpsoasis.org/download). By using the DL, the number of free peak parameters reduces notably, thereby improving the stability of the fitting process, reducing the uncertainties of peak parameters, and improving the reproducibility of results from different operators.

In this study, opal–magnetite photocatalysts based on SiO₂ artificial opal crystals infiltrated with different concentrations of Fe₃O₄ nanoparticles (NPs) were synthesized using a combination of lateral infiltration and co-assembly methods. By adjusting the concentration of Fe₃O₄ NPs in the SiO₂ opal crystal, the energy band gap (Eg) was tuned to enable efficient degradation of methylene blue (MB) under visible light (410 nm and 575 nm). The photocatalytic process involved two stages: MB adsorption on the surface due to charge differences in the composite film and subsequent degradation through oxidative radicals on the catalyst’s surface. The developed material exhibited potential for applications in water remediation.

This work introduces the Coupled-Resonances (CR) line shape as a theoretically robust model for analyzing asymmetric peaks in photoelectron spectra, broadly applicable across various materials. The CR line shape extends the conventional Lorentzian distribution by incorporating an interference term that contributes to the peak asymmetry. This new approach addresses limitations of the widely used Doniach- Šunjić (D&S) model, which is often applied beyond its intended scope of metals with high densities of states at the Fermi level due to a lack of viable alternatives. Unlike the DS line shape, the CR model is integrable, enabling its use in precise chemical composition calculations, and it consistently provides superior fits to experimental data. The CR model’s versatility is evident in its ability to simplify to a Lorentzian for a single resonance. However, with multiple resonance states, the total line shape is no longer a simple summation of individual peak contributions. Instead, a significant interference term emerges, profoundly contributing to the observed peak asymmetry and shifting the maximum peak intensity. This highlights the critical need to consider interference terms in multiplet calculations of lineshapes. The CR line shape has been implemented in the freely available software, AAnalyzer. While most asymmetric peaks are accurately described by CR Type-II (two resonances), some require CR Type-III (three resonances) for optimal fitting, as demonstrated in the included examples. Ultimately, the CR model offers a more accurate and versatile approach to analyzing asymmetric lineshapes in photoemission spectroscopy, with broad applicability to a wide range of materials, including metals.

The background signal in X-ray Photoelectron Spectroscopy (XPS) consists of extrinsic and intrinsic components. This study focuses on characterizing the intrinsic background, particularly its structure across an extended binding energy (BE) range beyond the vicinity of the main photoelectron peak. The structure of the intrinsic background in the extended region can be reproduced through a rich set of wide Gaussian peaks. In the near-peak region, the intrinsic background is successfully characterized using the empirical Shirley algorithm. Since the Shirley algorithm fails when applied to extended energy regions by overshooting the experimental signal, a modified version must be employed that decays beyond the near-peak region. We found that a functional form flat near the peak (as in the Shirley algorithm) decays in a Gaussian-like manner for higher binding energies, satisfactorily reproduces the experimental data, and allows for revealing the rest of the rich structure of the intrinsic background. For this reason, we termed it a narrow-Shirley (NS) background. The characterization of the structure of the extended region of the intrinsic background enables the qualitative exploration of its physical origin. Building on previous work linking the near-peak Shirley signal to Interchannel Coupling with Valence Band Losses (ICVBL), we propose and provide qualitative evidence that this ICVBL mechanism is responsible for the entire intrinsic background structure across the extended energy range; this mechanism involves the absorption of a photon by a participating core level. Two of the predictions of the ICVBL mechanism are tested by comparing the structure of the intrinsic background with Auger Electron Spectroscopy (AES) and X-ray Absorption Spectroscopy (XAS) data; a third prediction, the expected modulation of the intrinsic background with photon energies around the threshold of the participating core level, is tested through synchrotron experiments.