Electrochemical stability, physical, and electronic properties of thermally pre-formed oxide compared to artificially sputtered oxide on Fe thin films in aqueous chloride

Abstract

The electrochemical stability and corrosion behavior of the thermally pre-oxidized and sputter deposited variant of an oxide single-crystalline Fe thin film were compared. Thermal oxides formed Fe2O3 over an inner layer of Fe3O4 while the sputtered oxides were found to have grown Fe3O4 instead of the target stoichiometry of Fe2O3. Oxide films of both types were stable in pH = 9.3 borate buffer solution, however, were altered in pH = 9.3, 0.1 M NaCl solution in the case of thermally pre-oxidized Fe thin film. The stability of the oxide differed in pH = 4, 0.1 M NaCl where sputtered Fe films were more stable against acidic chemical dissolution than the thermally formed Fe oxide film. These differences were traced by AC/DC electrochemical analysis including electronic defect densities, and molecular identity characterized by ex-situ X-ray photoelectron spectroscopy.