![]() ![]() ![]() By controlling the crystal plane orientation and termination during film growth, polar surfaces, and interfaces can be obtained, where structural distortions form due to the interaction of short-range covalency and long-range electrostatic effects 11, 12, 13, 14. ![]() ![]() Polarity at interfaces and surfaces in complex oxide thin films plays a critical role in their physical and chemical properties such as ferroelectricity 1, 2, 3, 4, 5, 6, 7, superconductivity 8, magnetism 9, and catalysis 10. These findings provide insights into the understanding and evolution of surface polarity at the atomic level. Our results suggest that the strong surface reconstruction in the reduced sample is closely related to the formation of oxygen vacancies from topochemical reduction. 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). Its spatial depth extent is about three unit cells from the surface. We observe a polar distortion coupled with octahedral rotations in a fully oxidized Pr 0.8Sr 0.2NiO 3 sample, and a stronger polar distortion in a partially reduced sample. In this study, we use annular bright-field imaging to investigate the surface structure of a Pr 0.8Sr 0.2NiO 2+ x (0 < x < 1) film. Understanding the mechanism behind these effects requires knowledge of the atomic structure and electrostatic characteristics at the surface. The polarity of a surface can affect the electronic and structural properties of oxide thin films through electrostatic effects. ![]()
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