Atomic-scale study of low-dimensional features in ferroelectric thin films

Due to their spontaneous polarization, ferroelectric materials have a variety of applications in electronic, optical, and electromechanical devices. In addition, recent advances in atomic-level control of thin film growth techniques, including molecular beam epitaxy and pulsed laser deposition, have made it possible to grow ferroelectric thin films with low-dimensional features leading to the discovery of many new phenomena and functional properties stemming from the coupling between the ferroelectricity and the low-dimensional features. However, since the features are usually in nano- or atomic- size, conventional characterization techniques have low spatial resolutions cannot accurately resolve these tiny features. Herein, I reported a comprehensive atomic-scale characterization method to study the low-dimensional features in ferroelectric materials using advanced transmission electron microscopy (TEM) techniques, including in situ TEM, scanning TEM (STEM), 4-dimensional STEM (4D STEM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). This opens new opportunities for studying both the mechanisms for how macroscopic properties can emerge from atomic-scale phenomena and the fundamental physics of ferroelectricity.First, we systematically study the spontaneous polarization induced positive/negative charge accumulation at ferroelectric-insulator interface. Second, we show dislocation-assisted BiMnOx nanochannels embedded in SrTiO3/La0.67Sr0.33MnO3 thin films having diode-like behavior. Finally, we demonstrate superelasticity and domain switching of freestanding BiFeO3 films using in situ straining and biasing TEM, respectively. During the in situ straining experiment, the film shows an unprecedented tremendous lattice strain up to 34.4%, which is two orders of magnitude higher than their bulk counterparts and comparable to ductile metals