Surface modification of iron oxides by ion bombardment - Comparing depth profiling by HAXPES and Ar ion sputtering

Thin films of the iron oxide maghemite (γ-Fe2O3) and hematite (α-Fe2O3) grown on fluorine doped tin oxide (FTO) with pulsed chemical vapour deposition have been investigated with hard X-ray photoelectron spectroscopy. It is found that even low energy sputtering induces a reduction of the surface layer into FeO. Satellites in the Fe 2p core level spectra are used to determine the oxidation state of iron. Depth profiling with changing photon energy shows that the unsputtered films are homogeneous and that the information obtained from sputtering thus, in this instance, represents sputter damages to the sample.