Impedance investigation of thermally formed oxide films on AISI 304L stainless steel

Thin oxide layers on 304L stainless steel were grown by thermal oxidation at 300 °C at different durations ranging from 2 to 4 h. The structural characterization of the oxide films was carried out by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy was used to investigate the effects of exposure time and applied potential on the electronic properties of these films. Oxide films are described by a multilayer structure, with n-type iron oxide and oxyhydroxide in the outer layers and p-type chromium oxide in the inner layer. Doping densities evaluated from Mott–Schottky plots increased with the oxidation duration, with characteristics of highly disordered semiconductor.