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Studies of Local Structural Distortions in Strained Ultrathin BaTiO3 Films Using Scanning Transmission Electron Microscopy

Published online by Cambridge University Press:  21 March 2014

Daesung Park ,
Anja Herpers ,
Tobias Menke ,
Markus Heidelmann ,
Lothar Houben ,
Regina Dittmann  and
Joachim Mayer
Daesung Park*
Affiliation:
Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstrasse 55, D-52074 Aachen, Germany Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, D-52425 Jülich, Germany
Anja Herpers
Affiliation:
Peter-Grünberg-Institute 7, Forschungszentrum Jülich, D-52425 Jülich, Germany
Tobias Menke
Affiliation:
Peter-Grünberg-Institute 7, Forschungszentrum Jülich, D-52425 Jülich, Germany
Markus Heidelmann
Affiliation:
Peter Grünberg Institute 5, Forschungszentrum Jülich, D-52425 Jülich, Germany Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, D-52425 Jülich, Germany
Lothar Houben
Affiliation:
Peter Grünberg Institute 5, Forschungszentrum Jülich, D-52425 Jülich, Germany Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, D-52425 Jülich, Germany
Regina Dittmann
Affiliation:
Peter-Grünberg-Institute 7, Forschungszentrum Jülich, D-52425 Jülich, Germany
Joachim Mayer
Affiliation:
Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstrasse 55, D-52074 Aachen, Germany Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, D-52425 Jülich, Germany
*
*Corresponding author.park@gfe.rwth-aachen.de
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Abstract

Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

Keywords

ferroelectricitybariumtitanateEELSHAADFcrystal field splittingepitaxial strainStripeSTEM
Type
EDGE Special Issue
Information
Microscopy and Microanalysis , Volume 20 , Issue 3 , June 2014 , pp. 740 - 747
Copyright
© Microscopy Society of America 2014 

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