Modified Oxygen Defect Chemistry at Transition Metal Oxide Heterostructures Probed by Hard X-ray Photoelectron Spectroscopy and X-ray Diffraction

Transition metal oxide heterostructures are interesting due to the distinctly different properties that can arise from their interfaces, such as superconductivity, high catalytic activity, and magnetism. Oxygen point defects can play an important role at these interfaces in inducing potentially novel properties. The design of oxide heterostructures in which the oxygen defects are manipulated to attain specific functionalities requires the ability to resolve the state and concentration of local oxygen defects across buried interfaces. In this work, we utilized a novel combination of hard X-ray photoelectron spectroscopy (HAXPES) and high resolution X-ray diffraction (HRXRD) to probe the local oxygen defect distribution across the buried interfaces of oxide heterolayers. This approach provides a nondestructive way to qualitatively probe locally the oxygen defects in transition metal oxide heterostructures. We studied two trilayer structures as model systems: the La 0.8 Sr 0.2 CoO 3−δ /(La 0.5 Sr 0.5 ) 2 CoO 4−δ /La 0.8 Sr 0.2 CoO 3−δ (LSC 113 /LSC 214 ) and the La 0.8 Sr 0.2 CoO 3−δ /La 2 NiO 4+δ /La 0.8 Sr 0.2 CoO 3−δ (LSC 113 /LNO 214 ) on SrTiO 3 (001) single crystal substrates. We found that the oxygen defect chemistry of these transition metal oxides was strongly impacted by the presence of interfaces and the properties of the adjacent phases. Under reducing conditions, the LSC 113 in the LSC 113 /LNO 214 trilayer had less oxygen vacancies than the LSC 113 in the LSC 113 /LSC 214 trilayer and the LSC 113 single phase film. On the other hand, LSC 214 and LNO 214 were more reduced in the two trilayer structures when in contact with the LSC 113 layer compared to their single phase counterparts. The results point out a potential way to modify the local oxygen defect states at oxide heterointerfaces.