Preparation and investigation of the A-site and B-site terminated SrTiO₃(001) surface: A combined experimental and theoretical x-ray photoelectron diffraction study

We have investigated surface composition, structure, and termination of $SrTiO3(001)$ samples (STO) following typical steps of standard ex situ and in situ preparation procedures by performing x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD) experiments, and multiple scattering cluster (MSC) calculations. XPS has confirmed the presence of $Sr2+, Ti4+$⁠, and $O2-$related to STO. Well-developed diffraction features have been observed in all XPD polar scans demonstrating the good structural ordering of the investigated surfaces. In order to permit a detailed comparison of XPD experiment and theory, we have especially taken care of effects due to the angular dependent instrument function by applying a new ratio procedure. Thus, we achieved a very good agreement between results of MSC calculations and experimental angular distributions. A fingerprint region has been identified in Sr3d polar scans, which has exhibited both evident dependencies on surface preparation steps in the experiments and clear sensitivity to surface termination in the theoretical modeling. In this manner, we have been able to describe as-received samples and in situ-treated samples as being $TiO2$- and SrO-terminated, respectively. Standard buffered hydrofluoric acid-treated samples turned out to be mostly $TiO2$-terminated but with a non-negligible admixture of different, likely SrO-type termination.