BULK METAL-OXIDES AS A MODEL FOR THE ELECTRONIC-PROPERTIES OF PASSIVEFILMS

The aim of the present work is to compare the electronic properties of natural passive films on iron and chromium with sintered bulk metal o xides. The characterization of the semiconductive properties of variou s bulk oxides shows that the passive film on iron can be simulated by highly doped Fe2O3. The doping concentration of Fe-oxides is determine d by their Fe2+ content. At a dopant level of approximate to 5.10(20) cm(-3) in Fe2O3 the flatband potential, bandgap energy, intensity of t he photocurrent, and the doping concentration are in good agreement wi th the natural passive film. A major advantage in using sintered bulk oxides as models for natural passive films is that oxide properties ca n be separated from effects associated with the underlying substrate. Therefore it could be shown, e.g., that the photocurrent behavior in t he case of passive film on iron and chromium is mechanistically determ ined by interband transitions and is not caused by a photoemission pro cess from the underlying metal. Further, investigations of bulk Fe-oxi des revealed that their chemical stability is determined by the Fe2+ c ontent and can be significantly improved by Cr2O3 addition.