Strain evolution in La₀.₆Sr₀.₄CoO₃₋δ and SrTi₀.₃Fe₀.₇O₃₋δ multilayer systems

Abstract

In this work, we investigated La₀.₆Sr₀.₄CoO₃₋δ / SrTi₀.₃Fe₀.₇O₃₋δ multilayer systems with different layer thicknesses. Reciprocal space mapping showed splitting of the reflections in the sample with 5 nm layers while for 15 nm thick layers reflections have been elongated. Using transmission electron microscopy, we investigated this phenomenon at the atomic scale and showed that the alternating 15 nm layers gradually increase their tensile out-of-plane strain, whereas the sample with 5 nm layers maintains a relatively stable strain state. In-plane strain relaxation is similar in both samples. Still, it differs in the strain relaxation mechanism, which involves the formation of amorphous regions in the 5 nm sample and the formation of edge dislocations in the 15 nm sample. Electron energy loss spectroscopy was employed to probe the oxidation states of Co, Fe, and Ti. In both samples, the oxygen vacancy concentration increases toward the surface.