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

Atomically-resolved mapping of polarization and electric fields across ferroelectric-oxide interfaces by Z-contrast imaging
장혜정S.V. KalininA.N. MorozovskaM. HuijbenY.H. ChuP. YuR. RameshE.A. EliseevG.S. SvechnikovS.J. PennycookA. Borisevich
ferroelectric; STEM; Z-contrast image; TEM; polarization; electric field; interface; BFO; LSMO
Issue Date
Advanced materials
VOL 23, NO 21, 2474-2479
To summarize, we used direct structural imaging using aberration-corrected STEM to map polarization fi elds at the BFO-LSMO interface. In the thicker fi lm, the polarization is found to decay within the ferroelectric phase over 3–5 unit cells and is essentially zero at the interface. In the LSMO phase, the formation of a polarized layer opposite to the BFO polarization is observed. Hence, the interface forms an effective head-to-head domain wall. In contrast, in the thin fi lm the polarization in the ferroelectric phase and LSMO are collinear, and the interface is formed by a stable head-to-tail arrangement. These observations are consistent with strong interface polarization pinning at the BFO-LSMO interface. This frozen polarization will signifi cantly affect the polarization switching in these systems and result in the presence of large interfacial fi elds. In particular, in thin LSMO the polarization is apparently controlled by the interface charge, and only weakly affected by the ferroelectric polarization of the fi lm. Using modifi ed LGD theory, we have then extracted the numerical values of interface and polarization charges at the interface from the experimental displacement profi les. Notably, the modeling results reinforce the suggestion of a pivotal role that interface charge (a.k.a. polar discontinuity) plays in the properties of these interfaces. In a more general perspective, these results show how electrostatic fi elds can be directly mapped in ferroelectric materials on the atomic level through the detection of associated structural distortions. This provides an alternative methodology to holography, which requires a thin fi lm near a region of vacuum to allow interference between the transmitted and reference beams.
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