Simulation of STEM-HAADF Image Contrast of Ruddlesden–Popper Faulted LaNiO3 Thin Films

LaNiO3 (LNO) thin films are widely used as electrode materials. Yet, their properties greatly depend on such parameters as strain state and defect density. In this work, we present a detailed structural characterization of epitaxial LNO thin films grown on LaAlO3(001). A noticeable lack of contrast between La/Ni ions occurs in selected areas as seen by scanning transmission electron microscope, high-angle annular dark-field imaging (STEM-HAADF). By using atomistic modelization and image simulations, we show that this effect, rather than signaling cation interfusion or other spurious effects, results from different Ruddlesden-Popper faulted combinations with 1/2a⟨111⟩ relative displacement of defect free perovskite blocks, in the LaNiO3 perovskite