XPS and UPS examinations of Fe53Ni and Fe10Ni in 1 <scp>M</scp> NaOH and 0.005 <scp>M</scp> H ₂ SO ₄

Abstract

Abstract The formation of passive films as a function of time and potential on Fe53Ni in 1 M NaOH in 0.005 M H 2 SO 4 + 0.495 M K 2 SO 4 and on Fe10Ni in 1 M NaOH was studied by XPS. In order to avoid air oxidation and to minimize contamination of the samples, an electrochemical specimen preparation and transsfer system attached to the ultrahigh vacuum (UHV) system was used. Quantitative evaluation of the data yields the total thickness and the composition of passive layers. Characteristic changes of the spectra in the transpassive range for Fe53Ni in the alkaline electrolyte, which include a shift of the peaks of the oxide components to lower binding energies, are observed. They are interpreted as a decrease of the Fermi level towards the valence bend as the result of the oxidation of Ni (OH) 2 to NiOOH. This is supported by UPS measurements in dependence of the passivation potential of the specimen, which show an increase in work function corresponding to the Fermi level shift.