Advanced Electron Microscopy for Epitaxial Oxide Thin Films

Epitaxial oxide thin films and their heterostructures provide a rich platform for discovering emergent phenomena, including high-temperature superconductivity, novel magnetic states, and ferroelectricity. The functionality of these systems is governed by their atomic-scale structure and the complex structural dynamics they exhibit, such as phase transitions and domain switching. Elucidating the mechanisms underpinning these behaviors consequently necessitates characterization at the highest attainable spatial resolution. This talk will demonstrate a multi-modal approach using scanning transmission electron microscopy (STEM) to probe these intricate behaviors. First, we combine conventional atomic-resolution imaging with in-situ external stimuli to directly visualize the phase transitions and ferroelastic switching in fluorite-structured ZrO₂ [1]. To overcome the limited sensitivity to light elements in conventional STEM imaging, integrated differential phase contrast (iDPC) STEM is employed to precisely map the critical oxygen displacement and the corresponding ferroelectric switching [2]. Finally, to transcend conventional resolution limits and achieve three-dimensional (3D) insights, we introduce state-of-the-art multislice electron ptychography (MEP) that provides super-resolution imaging beyond the diffraction limit and enables the reconstruction of the 3D structural information. We will further discuss the application of MEP in several key areas: the discovery of 3D structural inhomogeneity in Hf_0.5Zr_0.5O₂ and BiFeO₃ thin film [3,4]; high-precision mapping of FeO₆ oxygen octahedral tilts in epitaxial antiferromagnetic heterostructures; and chiral-polar reconstruction in atomically bonded, twisted oxide moiré superlattices.