Double Lorentzian lineshape for asymmetric peaks in photoelectron spectroscopy

Abstract

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.