Hassel and Marianne Ledbetter MatSE Colloquium - "Local structure in Novel Ferroelectrics: Insights from Scanning Transmission Electron Microscopy"

The recent discovery of fluorite- and wurtzite-structured ferroelectrics with robust polarization reversal and CMOS-compatible processing provides new opportunities for integrated ferroelectrics. To understand the mechanisms that control and induce switchable states in such materials, including the influence of microstructure and electrode interfaces, we use a variety of transmission electron microscopy (TEM) and spectroscopy techniques to study and quantify structure from the micrometer down to sub-ångstrom length-scales. In particular, scanning TEM (STEM) imaging is utilized to determine projected atomic column positions from both the heavy and light-element sublattices. These structural data are subsequently used to calculate partial pair distribution functions and local spontaneous polarization. The atomic- to meso-scale structural and chemical insights gleaned from the STEM-based microscopy– including those associated with interfaces, grain boundaries, domain boundaries and their interactions– are invaluable for understanding polarization phenomena in these wurtzite ferroelectrics. Furthermore, in-situ biasing experiments provide insight into domain nucleation and domain wall propagation, which are topics of active investigation and distinct in behavior from perovskite ferroelectrics.