Atomically resolved mapping of polarization and strain across ferroelectric oxide interfaces by Z-contrast imaging

Atomically resolved mapping of polarization and strain across ferroelectric oxide interfaces by Z-contrast imaging
장혜정Stephen J. PennycookAlbina Y. Borisevich
STEM; ferroelectric oxide; BFO
Issue Date
한국세라믹학회 추계학술대회
Polarization dynamics and oxygen octahedral tilts at the ferroelectric-metal interfaces is the dominant factor underpinning the functionality of ferroelectric devices including capacitors, direct data storage, field-effect transistors, and tunneling barriers. Their behavior at interfaces allows new functionalities that do not exist in the bulk, including interface superconductivity, improper ferroelectricity, and magnetoelectric coupling phenomena. Multiple theoretical studies have addressed the role of the mesoscopic space-charge layers, non-uniform polarization distributions, and details of chemical bonding at the ferroelectric-metal interface. However, despite the multitude of mesoscopic studies based on Ginsburg-Landau-Devonshire (GLD) theory and multiple recent density functional theory based studies, experimental studies of the polarization behavior at ferroelectric-metal interfaces have been much more limited. Here, we use aberration-corrected Scanning Transmission Electron Microscopy (STEM) to do direct imaging of atomic structure which provides us with insights into properties of the perovskite oxides. This is powerful tool for imaging sub-angstrom structural distortions such as polarization-related displacements, oxygen octahedral tilting and lattice parameters unitcell by unitcell in ferroelectrics. In addition, STEM combined with electron energy-loss spectroscopy (EELS) makes it possible to analyze the composition and the dielectric property simultaneously with the atomic structure. As a result, we can clearly separate the contributions of interface charge from polarization charge at the interface, and extract a complete description of the electrostatic field distribution across the heterostructure. In this work, the direct image of interface between BiFeO3 thin film and the half-metal buffer layer (La,Sr)MnO3 will be shown regarding the effect of polarization and charge compensation.
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