An Electron Diffraction Study of Thin Oxide Films on Iron Single Crystals

Electron diffraction patterns from thin films of , formed at low temperatures on the (112) and (001) iron surfaces, exhibit diffuse spiking parallel to the {111} directions in reciprocal space. At higher temperatures, intensity maxima on these spikes are replaced by the strongest reflections from highly oriented , which grows with its oxygen planes parallel to those of the cubic oxide; (00.1) α // (111) spinel. The spikes about the strongest reflections of the spinel pattern are interpreted as evidence of stacking faults in the closest packed oxygen planes. The appearance of stacking faults is regarded as the first indication of the nucleation of in the films. On the (112) iron surface, develops in the outer layer of the oxide at an earlier stage than on the (001).