No abstract

Strain engineering of complex oxide heterostructures has provided routes to explore the influence of the local perturbations to the physical properties of the material. Due to the challenge of disentangling intrinsic and extrinsic effects at oxide interfaces, the combined effects of epitaxial strain and charge transfer mechanisms have been rarely studied. Here, we reveal the local charge distribution in manganite slabs by means of high-resolution electron microscopy and spectroscopy via investigating how the strain locally alters the electronic and magnetic properties of La0.5Sr0.5MnO3–La2CuO4 heterostructures. The charge rearrangement results in two different magnetic phases: an interfacial ferromagnetically reduced layer and an enhanced ferromagnetic metallic region away from the interfaces. Further, the magnitude of the charge redistribution can be controlled via epitaxial strain, which further influences the macroscopic physical properties in a way opposed to strain effects reported on single-phase films. Our work highlights the important role played by epitaxial strain in determining the spatial distribution of microscopic charge and spin interactions in manganites and provides a different perspective for engineering interface properties.

Halide perovskites (HPs) are promising candidates for optoelectronic devices, such as solar cells or light-emitting diodes. Despite recent progress in performance optimization and low-cost manufacturing, their commercialization remains hindered due to structural instabilities. While essential to the development of the technology, the relation between the microscopic properties of HPs and the relevant degradation mechanisms is still not well understood. The sensitivity of HPs toward electron-beam irradiation poses significant challenges for transmission electron microscopy (TEM) investigations of structure and degradation mechanisms at the atomic scale. However, technological advances and the development of direct electron cameras (DECs) have opened up a completely new field of electron microscopy: four-dimensional scanning TEM (4D-STEM). From a 4D-STEM dataset, it is possible to extract not only the intensity signal for any STEM detector geometry but also the phase information of the specimen. This work aims to show the potential of 4D-STEM, in particular, electron exit-wave phase reconstructions via focused probe ptychography as a low-dose and dose-efficient technique to image the atomic structure of beam-sensitive HPs. The damage mechanism under conventional irradiation is described and atomically resolved almost aberration-free phase images of three all-inorganic HPs, CsPbBr3, CsPbIBr2, and CsPbI3, are presented with a resolution down to the aperture-constrained diffraction limit.