X-ray standing wave assisted XANES for depth dependent chemical state analysis of Cr in Cr₂O₃/Cr bilayer structure

We report the detailed depth-dependent structural and chemical analysis of the Cr2O3/Cr bilayer structure deposited on Si <100> substrate. The non-destructive simultaneous X-ray reflectivity and grazing incidence X-ray fluorescence measurements were used for this purpose. Corresponding variation in the chemical state of Cr atoms as a function of depth has been studied using X-ray standing wave (XSW) assisted X-ray absorption near edge structure (XANES) measurements. Various oxidation states of Cr atoms present in the Cr2O3/Cr bilayer structure were determined using X-ray photoelectron spectroscopy (XPS). Depth-resolved XANES measurements confirmed the presence of chromium oxide (Cr2O3) and hydroxide (Cr (OH)3) at the top surface of the Cr2O3/Cr bilayer structure. The results also reveal the presence of metallic Cr along with its compounds Cr2O3 and Cr (OH)3 at the interface medium, showing significant mixing between the Cr2O3 and Cr layers. Our results clearly demonstrate that the XSW assisted XANES technique is extremely efficient for determining the variation of chemical states at the surface, interface, and different depths of a thin film structure. Such types of analysis are particularly useful for differentiating the presence of a metal from its own oxides, even at higher depths inside a thin film medium.