Sub‐Nanometer Depth Profiling of Native Metal Oxide Layers Within Single Fixed‐Angle X‐Ray Photoelectron Spectra

Abstract - Many metals form nanometer‐thin self‐passivating oxide layers upon exposure to the atmosphere, which affects a wide range of interfacial properties and shapes the way how metals interact with their environment. Such native oxide layers are commonly analyzed by X‐ray photoelectron spectroscopy (XPS), which provides a depth‐resolved chemical state and compositional analysis either by ion etching or modeling of the electron escape depths. The latter is commonly used to calculate the average thickness of a native oxide layer. However, the measurement of concentration profiles at the oxide‐metal interface remains challenging. Here, a simple and accessible approach for the depth profiling of ultrathin oxide layers within single fixed‐angle XPS spectra is proposed. Instead of using only one peak in the spectrum, as is usually the case, all peaks within the energy range of a standard lab device are utilized, thus resembling energy‐resolved XPS without the need for a synchrotron. New models that allow the calculation of depth‐resolved concentration profiles at the oxide‐metal interface are derived and tested, which are also valid for angular‐ and energy‐resolved XPS. The proposed method not only improves the accuracy of earlier approaches but also paves the way for a more holistic understanding of the XPS spectrum.