Oxygen crystallographic positions in thin films by non-destructive resonant elastic X-ray scattering

Precisely locating oxygen atoms in nanosized systems is a real challenge. The traditional strategies used for bulk samples fail at probing samples with much less matter. Resonant elastic X-ray scattering (REXS) experiments in the X-ray absorption near-edge structure (XANES) domain have already proved their efficiency in probing transition metal cations in thin films, but it is not feasible to perform such experiments at the low-energy edges of lighter atoms – such as oxygen. In this study, the adequacy of using REXS in the extended X-ray absorption fine structure (EXAFS) domain, also known as extended diffraction absorption fine structure (EDAFS), to solve this issue is shown. The technique has been validated on a bulk FeV₂O₄ sample, through comparison with results obtained with conventional X-ray diffraction measurements. Subsequently, the positions of oxygen atoms in a thin film were unveiled by using the same strategy. The approach described in this study can henceforth be applied to solve the crystallographic structure of oxides, and will help in better understanding the properties and functionalities which are dictated by the positions of the oxygen atoms in functional nanosized materials.