Oxidation of ultrathin iron layers on Cu(100): Composition of the oxide films

Abstract

The oxidation of Cu(100)Fe surfaces containing 0–2.7 ML of Fe was studied at room temperature using Auger electron spectroscopy, ellipsometry and low energy electron diffraction. The initial oxidation rate was independent of θ Fe which means that oxygen adsorption proceeds via a precursor mechanism. On all surfaces saturation of the oxidation occurred. For θ Fe< 2 all iron was oxidised to FeO 1.43 ± 0.07 (Fe 2O 3) and a surplus of θ O = 0.5 was present, probably at the Cu-Fe 2O 3 interface. For iron coverages exceeding 2 ML the oxidation stopped after the uptake of 3.3 ± 0.3 ML of oxygen. LEED experiments on a surface containing 0.8 ML of oxidised iron gave evidence for the formation of ordered domains of oxide in two (perpendicular) orientations. The distances of the spots indicate that a strong contraction of the oxide lattice takes place in order to match the Cu(100) lattice.