Oxidation effects on ultrathin Ni and Cr films grown on Fe(001): A combined scanning tunneling microscopy and Auger electron spectroscopy study

The effects of oxygen exposure on ultrathin films of Ni and Cr deposited on Fe(001) are studied by means of low energy electron diffraction, Auger electron spectroscopy and scanning tunneling microscopy. In the case of the Ni/Fe(001) oxidation we find that, since the first stages of oxygen exposure, Fe atoms segregate toward the sample surface, where their oxidation takes place. Post-annealing treatments in ultra-high-vacuum conditions promote the Fe oxidation and improve the order of the overlayer, leading to the stabilization of an atomically flat FeO(111)-like film covering the sample. On the other hand, the oxidation of the Cr/Fe(001) follows a different path. At low oxygen exposure only the Cr film is oxidized, while upon increasing the oxygen dose Fe oxidation takes place. The morphology resulting from the oxidation of such a system is rough and successive thermal treatments do not result in surface ordering.