COMPARISON OF THE SEMICONDUCTIVE PROPERTIES OF SPUTTER-DEPOSITED IRON-OXIDES WITH THE PASSIVE FILM ON IRON

The semiconducting properties of sputtered magnetite (Fe3O4) and oxidi zed magnetite layers with different Fe(II) contents were compared with the passive film on iron. Electrochemical impedance spectroscopy and photoelectrochemical experiments were carried out in berate buffer, pH 8.4. An evaluation of the impedance data according to the Mott-Schott ky concept showed that the capacitance of all films is linked with the ir doping concentrations rather than their thicknesses and that the do ping species of the passive film on iron is Fe(II). For the passive fi lm a potential-dependent doping concentration was found. Photoelectroc hemical investigation of the passive film and the sputtered oxide laye rs showed that for low doping concentrations, the photocurrent increas es with doping, whereas for high doping concentrations, an increase in doping leads to a decrease of the photocurrent. Possible causes for t his effect are discussed. Further, the combination of a light reflecta nce technique with photocurrent measurements allowed consideration of light absorption effects in the data treatment and separation of photo current contributions from the space-charge layer from film-thickness effects.