Passivation of Permalloy Thin Films: II . In Situ Characterization of the Oxide Layer by Photoelectrochemical and Impedance Measurements

Abstract

The formation of protective films, on thin films of Permalloy , and on metallic iron and nickel, by air‐annealing and by electrochemical oxidation in borate solution , was studied. The electronic types and energy gaps of the oxide films were investigated by an in situ measurement of the photocurrent response. The compositions were deduced from the spectral response and were confirmed by Raman and Auger electron spectroscopy. It is shown that the air‐formed oxides on Permalloy are iron oxides (n‐type and ). The oxide formed anodically on Permalloy is a p‐type . This oxide exhibits a nondirect transition, in addition to the direct one at 3.9 eV, which is obtained for crystalline . Such nondirect transition is characteristic of amorphous semiconductors but was not reported before for . The thicknesses of the films were calculated from the capacitance, obtained from impedance measurements. Mott‐Schottky plots were applied to the impedance data to evaluate the donor or acceptor density.