Revealing buried ferroelectric topologies by depth-resolved electron diffraction imaging

TL;DR

The paper introduces DREDI, a rapid, non-destructive electron diffraction imaging technique that maps three-dimensional ferroelectric textures with high spatial resolution, revealing complex buried topologies in nanomaterials.

Contribution

DREDI provides the first continuous polarization mapping across multiple length scales, uncovering hidden depth evolution of polar textures in ferroelectric films.

Findings

Revealed surface-to-bulk evolution of polar textures in BiFeO3 films.

Confirmed buried configurations with electron ptychography and modeling.

Identified mesoscale percolating networks of frustrated vertices.

Abstract

Nanoscale topological polar textures promise new functionalities for ferroelectric memories and logic, yet their three-dimensional structure and mesoscale organization remain experimentally inaccessible. Here we introduce depth-resolved electron diffraction imaging (DREDI), a fast, non-destructive, method that maps polarization with <50 nm lateral and <10 nm depth sensitivity within fraction of a second. Its high acquisition speed enables the first continuous polarization mapping across six orders of magnitude in length scale, from nanometers to millimeters. Using epitaxial BiFeO3 films, DREDI reveals a hidden depth evolution of polar textures: surface 71-degree stripes evolve into subsurface flux-closure vortices that bifurcate into three-fold vertices near the bottom interface. Cross-sectional multi-slice electron ptychography and phase-field modeling confirm these buried configurations and attribute them to strain heterogeneity and ferroelastic twinning in the SrRuO3 electrode. Large-area analysis further shows that vertex-like frustration forms a mesoscale percolating network above a critical length scale of 4 um. DREDI enables real-time, volumetric studies of buried topological textures in ferroic nanomaterials.