Investigation of atomic-scale decorations on mixed conducting oxides via time-of-flight secondary ion mass spectrometry (ToF-SIMS)

Sub-nanometer modifications of mixed ionic electronic conducting (MIEC) materials, like the perovskite La0.6Sr0.4CoO3-δ (LSC), represent a promising approach to improving their oxygen exchange kinetics and degradation stability. The complex interactions between decoration layers and the host material are still not fully understood and are a subject of current research. Under these circumstances, a novel approach using time-of-flight secondary ion mass spectrometry (ToF-SIMS) was developed to gain deeper insight into the electronic and chemical interactions of LSC with different oxidic decorations. The investigated samples were prepared by pulsed laser deposition (PLD) on YSZ single crystals, starting with a 100 nm thin LSC layer, which was then modified by sub-nm decorations of CaO, TiO2, and SnO2 (nominally 0.05 nm–0.5 nm) on top. By using ToF-SIMS with a sampling depth of 1–2 nm, it was possible to extract information simultaneously on the decoration layer and the host oxide. Significant differences in secondary ion (SI) intensities of the host material LSC were found that can be attributed to the formation of surface-near dipoles as a consequence of the acidic or basic nature of the decoration oxide. Further, relative stoichiometric variations of the La+, Sr+, and Co+ signals depending on the decoration oxide were observed, suggesting different preferential decoration sites on the LSC surface.