Challenges for integrating first principles theory and X-ray reflectivity measurements to predict interfacial structure

Determining atomic-scale structure, composition, and electronic properties of interfaces is crucial for technological applications but remains a challenge in liquid environments and under growth conditions. Defect sites on solvated catalyst surfaces change electron energy alignment between the surface and reacting molecules, impacting catalyst performance. Precise control of surface termination during epitaxial growth of novel materials is affected by processes such as dynamic layer rearrangement.

X-ray reflectivity (XRR) experiments probe the electron density of interfaces with high resolution but typically rely on model-dependent fitting to invert the data and obtain the corresponding atomic structure. First principles theory can predict energetically favorable surface structures but depends on approximations which can be inaccurate for defects and nonequilibrium processes. Integrating first principles theory with experimental XRR measurements using global optimization has the potential to determine interfacial structures more accurately than is possible through experiment or theory alone. Using the Al₂O₃/water interface and the SrTiO₃ surface during epitaxial growth as illustrative examples, this presentation explores the challenges and successes of such a combined approach.