4D-STEM Characterization of MBE-Grown Barium Titanate for Electro-Optic and Ferroelectric Devices

Synthesis and characterization of thin film barium titanate is of great interest due to its promise for use in electro-optic modulators [1]. These devices require a thin film with a high electro-optic coefficient that can operate at low voltages and integrate into photonic circuits, so barium titanate’s strong nonlinearity makes it an attractive candidate material. Barium titanate’s ferroelectricity means that it is also of interest for applications in nonvolatile ferroelectric memories. To pursue these applications, we must understand how variations in film stoichiometry affect the electro-optic properties, local atomic structure, and ferroelectric structure of thin film barium titanate. In this work, we use four dimensional scanning transmission electron microscopy (4D-STEM) and high-resolution imaging techniques to analyze the crystal structure thin films of barium titanate grown via molecular beam epitaxy. 4D-STEM can detect small movements of an electron beam due to local electric fields and therefore image the ferroelectric domains in barium titanate. High-resolution electron microscopy imaging allows us to evaluate atomic-level variations in crystal structure, local defects, and polarization in thin films of barium titanate.<br/><br/><b>Acknowledgements</b><br/>This work has been supported in part by the NSF STC for Integrated Quantum Materials DMR-1231319, and the NSF Nanotechnology Nanotechnology Coordinated Infrastructure ECCS-1541959.<br/><br/><b>References</b><br/>[1] C Wang, M Zhang, B Stern, M Lipson, M Loncar, "Nanophotonic lithium niobate electro-optic modulators," Optics Express 26, 1547 (2018).