Anomalous chemical shifts of Cu 2p and Cu LMM Auger spectra of silicate glasses

Abstract

Chemical states of copper ions in various kinds of silicate glasses were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray-induced Auger electron spectroscopy (XAES). Cu 2p photoelectron peaks of the melt-quenched Cu 2O–Al 2O 3–SiO 2 and Cu +/Na + ion-exchanged Cu 2O–Na 2O–Al 2O 3–SiO 2 glasses have the same binding energy assigned to Cu(I) state. On the other hand, Cu LMM Auger spectra show different spectral shapes in the respective glasses. Compared with the crystalline compounds Cu 2O and CuO and metallic Cu, the chemical shifts of the Cu LMM Auger lines are considered to represent the difference of the relaxation effect of the two-hole final state of Cu due to the electron donation ability of the surrounding elements around Cu in the glasses. Analysis of the spectra of Cu 2p and Cu LMM lines of the melt-quenched Cu 2O–Na 2O–SiO 2 glass shows remarkable X-ray irradiation effects. X-ray induces the Cu 2p peak shifts towards the lower binding energy side and finally it has a lower binding energy than that of metallic Cu. It is assigned to Cu(I) in octahedral coordination as found in the spinel structure. From the detailed analysis of Cu 2p spectra, the changes of the redox of Cu ion and the structural evolution on the glass surface are discussed.