Exploring Mechanisms of Ferroelectric Switching in Real Time Using In Situ TEM.

摘要

In this thesis, in situ biasing experiments on BiFeO3 thin film devices were enabled through the development of a specimen holder and sample electrode mask. The dynamics of ferroelectric domain propagation and nucleation were studied at varying electric fields, and at high spatial and temporal resolution using this in situ technique. A range of dynamic behavior is witnessed in the captured movies, including domain nucleation, propagation, switching, relaxation, and intermediate domain configurations. The dynamic interaction of domains and defects is studied. A network of misfit dislocations at the BFO film-substrate interface is found to alter domain morphologies and velocities. Threading dislocations are shown to stabilize intermediate domain configurations and radically slow domain relaxation, while also acting as pinning sites. A comparison of the observed domain kinetics is made to two popular models---the Kolmogorov-Avrami-Ishibashi model and Nucleation Limited Switching model. The influence of the arrays of dislocations on the domain kinetics in these BFO thin film devices more accurately fits the NLS model. Investigations into the influence of charged domain walls and charged defect clusters are presented. These findings, by revealing how the presence of defects and localized compositional changes play a role in domain wall motion behavior during electric field control, can help improve the design of future devices built upon ferroelectrics and multiferroics.