Electron holography using interference of electron wave is one of quantitative microscopic techniques to visualize electromagnetic fields at nanometer scale. The long standing problem in this method was that the observable area was limited near the sample edge. To solve this problem, we developed split-illumination electron holography [1]. In this method, a coherent electron wave is separated into two coherent waves (object and reference waves) using biprism placed in the illumination system. The coherence degree of these electron waves do not change when they are separated. This makes it possible to achieve high precision holographic observation of an area far from the sample edge. As one of applications, electrostatic potential analysis of oxide heterojunctions with polar discontinuity will be presented.
The discovery of the two-dimensional interface conduction in the LaAlO3/SrTiO3 (LAO/STO) heterojunction with polar discontinuity made a revival of the interest on the polar interface [2]. The emergence of high-mobility in LAO/STO is generally explained by the polar catastrophe scenario. Although the spontaneous electric polarization due to this charge redistribution was theoretically predicted, the existence of the mobile charges made it difficult to confirm the spontaneous polarization in LAO/STO junction. We explored oxide heterojunctions where the spontaneous polarization plays a dominant role in the charge screening and selected the LaFeO3 (LFO)/STO as target interface. Figure 1 shows two types of atomic sequences at the interfaces and reversal of electrostatic potential slopes in LFO. The results indicate that the originally non-polar LFO are converted into polar as a consequence of the polar catastrophe [3].
References
[1] T. Tanigaki, Y. Inada, S. Aizawa et al., Appl. Phys. Lett. 101, 043101 (2012).
[2] A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004).
[3] M. Nakamura, F. Kagawa, T. Tanigaki et al., Phys. Rev. Lett. 116, 156801 (2016).
Acknowledgements
This work was partly supported by the Japan Society for the Promotion of Science (JSPS) through its Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program), Grant-in-Aid for Young Scientists (A) (15H05426) and that for Scientific Research (24226002) from the MEXT of Japan, and CREST from Japan Science and Technology Agency (JST).
Figures:
Figure 1. Polarization controlled by atomic sequences at the LaFeO3 (LFO)/ SrTiO3 (STO) interfaces. (a) The atomic sequences of TiO2 junction and FeO2 junction evaluated by atomic-resolution energy-dispersive x-ray spectroscopy images. (b) Electrostatic potentials measured by electron holography and models of polarizations induced by bound charges at the interfaces.
To cite this abstract:
Toshiaki Tanigaki, Masao Nakamura, Fumitaka Kagawa, Hyun Soon Park, Tsuyoshi Matsuda, Daisuke Shindo, Yoshinori Tokura, Masashi Kawasaki; Split-illumination Electron Holography Applied to Electrostatic Potential Analyses of Oxide Heterojunctions with Polar Discontinuity. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/split-illumination-electron-holography-applied-to-electrostatic-potential-analyses-of-oxide-heterojunctions-with-polar-discontinuity/. Accessed: December 4, 2023« Back to The 16th European Microscopy Congress 2016
EMC Abstracts - https://emc-proceedings.com/abstract/split-illumination-electron-holography-applied-to-electrostatic-potential-analyses-of-oxide-heterojunctions-with-polar-discontinuity/