Electron Holography for Electromagnetic Materials by Daisuke Shindo & Zentaro Akase

Author:Daisuke Shindo & Zentaro Akase
Language: eng
Format: epub
ISBN: 9789819735372
Publisher: Springer Nature Singapore

Figure 3.44a shows the atomic structure and elemental distributions near the LFO = STO interfaces imaged by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS). The image shows that the elemental sequence was constructed as designed. From the STEM–EDS analysis, the broadening of the distribution was estimated at most 2 unit cells from the interface [74], which indicates that the interface is sufficiently abrupt for the interfacial atomic sequence to be classified into two definite types and that the effect of interfacial disorder is negligible. The absence of lateral conductivity in the LFO = STO junctions, irrespective of the interface terminations, was confirmed. Electron holography can directly quantify the spatial distribution of the electrostatic potential and, accordingly, the built-in internal electric field in a specimen [74]. Mappings of the electrostatic potentials for an electron is shown in Fig. 3.44b, where the junctions formed on the TiO2- and SrO-terminated STO surfaces are denoted as the TiO2 junction and the FeO2 junction according to the interfacial transition-metal layer, respectively. The electrostatic potential is almost uniform in the in-plane direction in both junctions. The electrostatic potential can now be examined in detail; Fig. 3.44c shows two examples of the electrostatic potential obtained along the dashed lines in Fig. 3.44b.

The spontaneous polarization dominates the electric polarization as shown by electron holography. The polarization direction can be switched by changing the chosen interfacial atomic sequence. Note that the emergent spontaneous polarization induces anomalous photovoltaic properties in the junctions, such as a sign reversal in the photocurrent that is dependent on the interfacial atomic sequence and the excitation photon energy.

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