Condensed-Matter Physics & Materials Science Seminar

As a prototypical example of functional oxides, ferroelectric materials have been utilized in a broad range of electronic, optical, and electromechanical applications and hold the promise for the design of future high-density nonvolatile memories and multifunctional nanodevices. The utilities of ferroelectrics are derived from the structures and switching of ferroelectric domains, or from their coupling to other material functionalities. In recent years, advanced imaging techniques based on aberration-corrected scanning transmission electron microscopy (STEM) and in situ transmission electron microscopy (TEM) have become powerful methods to characterize ferroelectric oxides, allowing nanoscale polarization states to be unambiguously determined with sub-Angstrom resolution, and allowing domain switching processes to be directly resolved in real time. In this presentation I will show several examples of applying advanced STEM or TEM-based techniques to the study of the static and dynamic properties of domains and domain walls in ferroelectric and multiferroic BiFeO3 thin films. Atomic structures and electrical switching behaviors of charged domain walls have been observed. A strong interaction between the ferroelectric polarization and nanoscale impurity defects has been discovered, and a new route to the production of exotic polarization states by utilizing such interaction has been proposed and established. These findings open up the possibility for the designing of novel ferroelectric materials and multifunctional devices with nanoscale structural defects or charged domain walls as essential components.