Comparative study of structural and semiconducting properties of passive films and thermally grown oxides on AISI 304 stainless steel

A comparative study including structural characterization and semiconducting properties of passive and thermally grown oxides on AISI 304 stainless steel is performed by near field microscopy, Auger electron spectroscopy, capacitance measurements and photoelectrochemistry. This comparative investigation is performed on thermally grown oxides at different temperatures and passive films formed at different potentials. The results obtained by characterization techniques show that the thickness of both oxides increases with increasing formation temperature and potential and allow discussing grain size and surface roughness vs. formation temperature. Capacitance measurements reveal semiconducting behavior of both iron and chromium oxides constituting whole passive and thermal oxides. These results allow extracting and discussing space charge layer thickness and doping densities of iron and chromium oxides in relation with formation conditions. The photocurrent results show a variation of the quantum efficiency with formation temperature and potential and a constant band gap value whatever the nature of the considered film. The variation of the quantum efficiency with applied potential in accordance with Pool–Frenkel model allow extracting and comparing donor densities with those obtained by capacitance measurements.

► Thermal oxides are thicker and more structured than passive films.
► Both passive and thermal oxide films exhibit the same semiconducting properties.
► For thermally grown oxides, the formation temperature effect is to increase thickness and reduce doping densities.
► In the case of passive films, the formaton potential acts as the same manner as temperature formation for thermal oxides.