Direct observation of strong surface reconstruction in partially reduced nickelate films.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38191551.
- Also identified by DOI 10.1038/s41467-023-44616-x and PMC identifier 10774438.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The polarity of a surface can affect the electronic and structural properties of oxide thin films through electrostatic effects. Understanding the mechanism behind these effects requires knowledge of the atomic structure and electrostatic characteristics at the surface. In this study, we use annular bright-field imaging to investigate the surface structure of a Pr<sub>0.8</sub>Sr<sub>0.2</sub>NiO<sub>2+x</sub> (0 < x < 1) film. We observe a polar distortion coupled with octahedral rotations in a fully oxidized Pr<sub>0.8</sub>Sr<sub>0.2</sub>NiO<sub>3</sub> sample, and a stronger polar distortion in a partially reduced sample. Its spatial depth extent is about three unit cells from the surface. Additionally, we use four-dimensional scanning transmission electron microscopy (4D-STEM) to directly image the local atomic electric field surrounding Ni atoms near the surface and discover distinct valence variations of Ni atoms, which are confirmed by atomic-resolution electron energy-loss spectroscopy (EELS). Our results suggest that the strong surface reconstruction in the reduced sample is closely related to the formation of oxygen vacancies from topochemical reduction. These findings provide insights into the understanding and evolution of surface polarity at the atomic level.