Speciation of Magnesium Surfaces by X‐Ray Photoelectron Spectroscopy (XPS)

ABSTRACT Magnesium metal, alloys, and salts have ubiquitous uses as structural materials, components in energy‐conversion devices, and catalysts. The surface states and reactions that underpin these applications are commonly studied by X‐ray photoelectron spectroscopy (XPS). Yet, reported binding energies for the Mg 2p transition vary widely, making accurate speciation of magnesium surfaces by XPS notoriously challenging. We found that these literature discrepancies result from differences between charge referencing procedures, particularly due to the unusually high binding energy of adventitious carbon on MgO and Mg(OH) 2 . Relevant pure and mixed samples were analyzed to assess the chemical speciation for magnesium. The range of Mg 2p binding energies was only 1.2 eV for pure samples, insufficient for speciation in many cases. The Mg KLL spectral lines were studied and found to provide additional chemical information due to final‐state effects. The range of the modified Auger parameter ( α ’), which is also independent of charging, was found to be 2.9 eV. The position and shape of the Mg KLL spectral lines are reported, and their use for the speciation of mixed systems is demonstrated. Moreover, a curve‐fitting procedure for O 1s signals was developed, which can separate MgO and Mg(OH) 2 despite their overlapping Mg 2p signals.