Probing Higher Order Topologies in Free Standing Ferroelectric Oxide Thin Films with STEM EELS and 4D-STEM

The combination of strain and electrostatic engineering in epitaxial heterostructures of ferroelectric oxides presents numerous opportunities for inducing new phases, complex polar topologies, and enhancing electrical properties. However, the predominant effect of substrate clamping can limit the electromechanical response, often relegating electrostatic effects to a secondary role. By releasing the mechanical constraints imposed by the substrate, the balance between elastic and electrostatic forces can be significantly altered, allowing them to compete equally. This release also activates new mechanical degrees of freedom, such as the macroscopic curvature of the heterostructure. In this work we explore the formation of higher order topologies and emergent phases in free standing ferroelectric and ferroelastic oxide thin films with atomic scale monochromated EELS and 4D-STEM.<br/>Using applied in-situ stimulus such as cooling, biasing and strain we induce the formation of higher order topologies while monitoring these exotic phases using in-situ EELS and 4D-STEM. Multimodal STEM EELS & 4D-STEM is ideal for characterization of the emergent ferroic phases, as the technique enables correlation of local chemistry and bonding information, with crystallographic, strain, polarisation, and magnetic field information determined from identical specimen regions at micro to (near) atomic scale. By automating the acquisition of EELS and 4D-STEM data with applied in-situ holder stimulus via Gatan software python scripting one can easily probe the dynamically formed emergent phases in these free standing thin films.