X-ray photoelectron spectroscopy: Silver salts revisited

The assignment of silver oxidation state by XPS is a matter of large controversy. In fact, a large discrepancy of binding energy values for its most intense peak, Ag 3d, exists in the literature. Auger parameter is useful to distinguish Ag(0) from other oxidation states but useless for identifying other oxidation states. In this work, using salts where Ag exists solely in the form of Ag (I), the oxides Ag2O and AgO and a mechanical mixture of them, we could demonstrate that Ag(I) and Ag(III) are identifiable much more by their peak shape and width than by their absolute binding energy. For the first time, the XPS peak fit was performed in a way compatible with the presence of Ag(I) and Ag(III) in AgO with 1:1 (v/v) stoichiometry as predicted by other properties, namely its diamagnetism.