Revealing oxide heterointerface induced phenomenon by atomic-resolution transmission electron microscopy

Zaoli Zhang1, U. Haselmann1, Yu.P. Ivan1, M. Kubicek2
1. Erich Schmid Institute, Austrian Academy of Sciences, Leoben, Austria
2. Vienna University of Technology, Vienna, Austria
Email: zaoli.zhang@oeaw.ac.at

Oxide heterostructure interfaces usually trigger novel physical phenomena. In this paper, two examples will be presented. Firstly, we reveal that Ca atoms segregate towards the interface of BiCaFeO3 films and strontium titanate (SrTiO3) substrate using atomic-resolution transmission electron microscopy (HRTEM). Consequently, Ca segregation triggers atomic and electronic structure changes at the interface. The phase contrast HRTEM image hardly changes while interface strain reduction, interplanar spacing variations, and oxygen vacancies at the interface have experienced significant variations. Fe valence state at the interface has also been evaluated. The experimental observations are validated by density functional theory (DFT) calculations [1].
Secondly, different structures of the La0.6Sr0.4CoO2.5 (LSCO) thin films grown in tensile (on SrTiO3) and compressive strain (LaAlO3) conditions were revealed using HRTEM/STEM. The pronounced domain structure of the Brownmillerite phase was found in tensile strained LCSO grown on the STO substrate. Oxygen vacancies ordering affected by strain from the substrate was observed. The structure peculiarity pertained to this oxide film strongly influences transport property, as revealed by the oxygen isotope exchange experiments [2].



The authors would like to thank A. Ghasemi (Erich Schmid Institute), J. Fleig (from Vienna University of Technology), M.N. Popov and L. Romaner (Materials Center Leoben Forschung GmbH, Leoben), J.Chen and Y. He (Hubei University, China), G. Haberfehlner, and G. Kothleitner (Graz Centre for Electron Microscopy), and A. Chuvilin (CIC nanoGUNE Consolider, San Sebastian, Spain). The financial support by the Austrian Science Fund (FWF): No. P29148-N36 is kindly acknowledged.

References
[1] Ulrich Haselmann, et al., ACS Appl. Mater. Interfaces 2020, 12, 12264-12274.

[2] Yurii P. Ivanov, et al., Communications Materials (2020) 1:25.