A quantitative surface analytical study of electrochemically‐formed copper oxides by XPS and X‐ray‐induced Auger spectroscopy

Electrochemically partially‐oxidized Cu specimens are transferred from the electrolyte (pH 13 and 14) within a closed system without air contact to the UHV and examined with XPS especially by interpreting the x‐ray‐induced Auger signal L 3 MM. The signal was fitted with standard spectra of clean Cu and Cu 2 O using an approximation by the Gauss/Lorentz curves. The oxide thickness calculated from the intensity ratio of the Cu 2 O and Cu signal with an appropriate value for the escape depth of the electrons agrees well with the evaluation of the electrochemical data. Angular dependent measurements permit a reliable examination of Cu 2 O of less than 0.5 monolayers. The water content of the oxide layer deduced from a quantitative evaluation of the O 1s XPS signal decreases with increasing thickness of Cu 2 O approaching less than 10% for ca . 10 monolayers. The small amount of hydroxide is located at the outmost layer. The growth of an outer CuO film leads to an increase of the hydroxide content to ca . 30%. These studies show that the Cu L 3 MM Auger signal may be used to evaluate quantitatively the amount of Cu 2 O.