Perovskite nickelates are interesting candidates to be used as electrode materials or in the research towards artificial superconductors. Among them, LaNiO3 (LNO) is of high interest because of its exceptional transport properties, with a resistivity lower than 100 µΩ·cm, and the potential tuning of electrical and magnetic interactions through appropriated strain engineering. A precise control of the stoichiometry, structural phases, lattice distortions and the presence/absence of dislocations/defects is critical to make LNO electrodes and related heterostructures suitable for electronic applications1–3.
Frequent defects present in perovskite structures are Ruddlesden Popper (RP) faults which consist on the relative displacement of two perfect defect free perovskite ABO3 blocks a distance of half- unit cell along the  direction. The earlier observations of RP faults were based on diffraction results, but they have also been imaged using advanced microscopy tools4,5. When observed along the  zone axis, this defect appears as a zig-zag arrangement of the A cations with a BO2 plane lost at the defect boundary.
In the present work we focus our attention on the characterization of RP faults observed in LNO thin films 14 nm and 35 nm thick, grown by pulsed laser deposition on (001) oriented LaAlO3 (LAO) single crystal substrates at an oxygen pressure P = 0.15 mbar and at a temperature T = 700°C. The preliminary characterization of the layers by high resolution transmission electron microscopy (HREM) and electron diffraction, confirmed the good pseudo-cube-on-cube epitaxial growth with atomic-sharp interfaces and the expected LNO(001)//LAO(001) epitaxial relationship, despite the compressive strain driven by the 1% mismatch between LNO (3.838 Å) and LAO (3.795 Å). Nevertheless, defects identified as potential RP faults oriented in both  and  directions were also observed.
Detailed high angle annular dark field (HAADF) imaging of these defects enabled a better identification of the defects as Ruddlesden Popper type through the appropriated correlation of the contrast of the atomic columns with cationic La(A) and Ni(B) positions as shown in the figure 1.
We will systematically address the interpretation of the contrast of these HAADF images through STEM-HAADF simulations calculated through the multislice procedure6 from atomistic models based on different arrangements of defect free perovskite blocks with octaetrahedral Ni3+ coordination (Fig. 2). Gradual variation of Z-contrast is interpreted in terms of the average of the atomic numbers of the La and Ni in A and B sites in RP displaced overlapping perovskite crystals7. The good agreement between the experimental images and the simulated ones (Fig. 3) validates the proposed geometrical configurations of the RP faulted crystals.
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2. Zhu, M. et al. Effect of composition and strain on the electrical properties of LaNiO3 thin films. Appl. Phys. Lett. 103, 141902 (2013).
3. Detemple, E. et al. Polarity-driven nickel oxide precipitation in LaNiO3-LaAlO3 superlattices. Appl. Phys. Lett. 99, (2011).
4. Beznosikov, B. V & Aleksandrov, K. S. Perovskite-Like Crystals of the Ruddlesden – Popper Series 1. Crystallogr. Reports 45, 864–870 (2000).
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7. Detemple, E. et al. Ruddlesden-Popper faults in LaNiO3/LaAlO3 superlattices. J. Appl. Phys. 112, 1–6 (2012).
To cite this abstract:Catalina Coll, Lluís López-Conesa, Cesar Magén, Florencio Sanchez, Josep Fontcuberta, Sònia Estradé, Francesca Peiró; Simulation of STEM-HAADF image contrast of Ruddlesden Popper faulted LaNiO3 thin films. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/simulation-of-stem-haadf-image-contrast-of-ruddlesden-popper-faulted-lanio3-thin-films/. Accessed: December 4, 2023
EMC Abstracts - https://emc-proceedings.com/abstract/simulation-of-stem-haadf-image-contrast-of-ruddlesden-popper-faulted-lanio3-thin-films/