Photoelectron holography characterization of protonated brownmillerite SrCoO_2.5 epitaxial films

Abstract

We characterized protonated SrCoO_2.5 epitaxial films by the photoelectron holography technique. We found that photoelectron holography patterns change due to cation displacements induced by electrochemical protonation. By simulating holography patterns based on structural models of the protonated SrCoO_2.5 using machine-learning enhanced global optimization and comparing them with the experimentally observed patterns, we evaluated hydrogen concentration and cation displacements in protonated SrCoO_2.5 films. Our results show that photoelectron holography is useful in characterizing protonation-induced changes in metal transition oxides.