Probing the Surface Polarization of Ferroelectric Thin Films by X-ray Standing Waves

In this study, we demonstrate that the X-ray standing wave technique in combination with X-ray photoelectron spectroscopy can provide the amplitude and orientation of the local ferroelectric polarization near the surface of a ferroelectric thin film. The X-ray standing wave technique provides Ba and Ti atomic positions, and thus the local ferroelectric polarization, within the topmost 3 unit cells below the surface of three differently strained BaTiO₃ thin films grown on scandate substrates, with a SrRuO₃ film as bottom electrode. We interpret the measured polarization profiles based on the kind, content and spatial distribution of oxygen-containing adsorbates at the surface.