X-ray depth profiling of iron oxide thin films

A nominally γ-Fe₂O₃ thin film (oxidized from an Fe₃O₄ film) has been structurally depth profiled using x-ray scattering in a grazing incidence, asymmetric Bragg geometry. By varying the grazing incidence angle, the x-ray penetration depth is varied from tens of Angstroms to several thousand Angstroms, slightly larger than the film thickness. At small incidence angles a diffraction pattern characteristic of α-Fe₂O₃ is observed, while at larger angles the pattern is predominantly from γ-Fe₂O₃, showing that there is a surface layer of α-Fe₂O₃. These results are quantified and the thickness of the α phase found to be 90 Å. The presence of the α phase explains a nonferromagnetic layer observed previously. These data together with magnetic and chemical data suggest that the nonferromagnetic layer forms during oxidation of the Fe₃O₄ film due to outward diffusion of Fe ions and their subsequent oxidation to form α-Fe₂O₃