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Aberration-corrected STEM Imaging and EELS Mapping of BaTiO3/SrTiO3 Interfacial Defects

Barium titanate (BaTiO3, or BTO) is highly promising for applications in ferroelectric field-effect transistors (FETs) because of its substantial polarization (0.2 C/m), high permittivity (1200) and roomtemperature ferroelectricity (TC = 120 oC). Unlike bulk BTO, the properties of BTO thin films are strongly affected by the film thickness, internal strain, and BTO/substrate interface structure, and it is crucial to control the interfacial energy by choosing an appropriate buffer layer or a suitable substrate. In this work, BaTiO3 (BTO)/ SrTiO3 (STO) heterostructures were grown by molecular beam epitaxy using Nb:SrTiO3 (001) substrates. Samples suitable for TEM observation were prepared via mechanical polishing followed by argon-ion-milling at liquid-nitrogen temperature. Aberration-corrected STEM images were recorded using a JEOL ARM 200F operated at 200 keV. The beam convergence angle was set at 20 mrad, and the collection angles were 0-22 mrad for LABF imaging and 90-150 mrad for HAADF imaging. EELS was carried out with a NION UltraSTEM100 operated at 100 keV.