Insight note: X‐ray photoelectron spectroscopy (XPS) peak fitting of the Al 2p peak from electrically isolated aluminum foil with an oxide layer

X‐ray photoelectron spectroscopy (XPS) is the most widely used and important method for chemically analyzing and speciating surfaces. XPS has surface sensitivity (5–10 nm), is quantitative, and is able to probe the oxidation states of the elements at surfaces. However, during the past few years, a great deal of incorrect XPS data analysis has entered the scientific literature. Accordingly, efforts, including this Insight Note, are being made to provide tutorial information to the scientific community. Aluminum is a scientifically and technologically important element. Here we discuss approaches for fitting the Al 2p peak envelope from a sample of aluminum foil with a thin layer of oxide on it. Signals from the metal and oxide are present. We discuss methods for electrically isolating (or not isolating) the sample during data acquisition, the choice of the baseline, fitting the oxide peak with one or two synthetic peaks, and fitting the metal signal with two symmetric or two asymmetric peaks. The thickness of the oxide is calculated based on the areas of the oxide and metal signals.