Origin of chemical shifts in K 2p x-ray photoelectron spectra

The interpretation of core-level binding energy (BE) chemical shifts measured by XPS can be complex and sometimes incorrect, since theу are often contributed to multiple mechanisms. This work deals with K 2p BE shifts on the basis of experimental data on a PHI5000 VersaProbeII spectrometer and theoretical calculations of binding energies for the core-K 2p level using the Δ Self-Consistent Field method. The experimental samples were KNbO3 cleaves and wafers before and after irradiation with atom and cluster beams of argon ions, as well as potassium hydrocarbonate and carbonate powders. Furthermore, our earlier data on KNN ceramics containing the K6Nb10.8O30 phase were used. The first-principle theoretical calculations were carried out for the KNbO3, K6Nb11O30, K2CO3, K2O, and KOH potassium compounds. We show that all the theoretically calculated and experimentally studied shifts have negative values. A good agreement between the calculated and measured shifts was obtained. The greatest negative shifts relative to the metallic potassium (−3.1 eV) were obtained for KNbO3 single crystals and KNN ceramics. Irradiation of KNbO3 with argon ions and clusters yielded additional spectra in the region of smaller shifts. The K 2p BE shifts of the other tested potassium compounds are in a broad region from −1.5 to −2.1 eV, and therefore additional features should be used for their correct interpretation.