|M.Sc Student||Lev Uri|
|Subject||Characterization of Ferroelectric Domains in Epitaxial|
Films of BaTiO3 by HRSEM and HRXRD
|Department||Department of Materials Science and Engineering||Supervisor||Professor Emeritus Emil Zolotoyabko|
Future applications of ferroelectric thin films require thorough understanding of the domain structure. At the moment, there is no technique that could be used to image domains on a nm-scale with adequate temporal resolution. The goal of this research was to explore the possibility to visualize ferroelectric domains on a nm-scale with low energy electrons emitted from the surface of ferroelectric thin films, including the electrons arising under X-ray irradiation.
Experimental part of this work was performed with epitaxial BaTiO3 films, 100-1000 nm thick, grown by MOCVD on MgO substrates. High-resolution X-ray diffraction was used to characterize the film microstructure and domain structure. We found strong correlation between the strain state of the films and an amount of specific material discontinuities, observed by high resolution SEM. The obtained results are explained by considering lattice misfit arising at the interface between in plane-oriented 90o-domains.
Existence of the 90o-oriented domains in our films was confirmed by in situ SEM measurements under strong external electric fields (up to 6 MV/m), which were applied to inter-digital electrodes (IDE) deposited on top of the films. In these measurements, time-dependent domain rearrangements induced by electric field were visualized by taking SEM movies.
X-rays photoemission electron microscopy (XPEEM) measurements with BaTiO3 films were conducted at the Nanospectroscopy beamline of the synchrotron ELETTRA, Trieste, Italy. Due to the insulating properties of ferroelectric films, severe surface charging was the major experimental challenge to overcome. This was achieved by grounding an array of gold IDE deposited on top of the films. Our measurements indicate that despite some residual charging, a 50 nm lateral resolution can be achieved in XPEEM measurements with ferroelectric films.