High-resolution transmission electron microscopy study on strained epitaxial manganite thin films and heterostructures

Abstract Pulsed laser deposition has been used to grow epitaxial La2/3Sr1/3MnO3 and La2/3Ba1/3MnO3 thin films as well as La2/3Ba1/3MnO3/SrTiO3 heterostructures. The microstructure was studied by four-circle X-ray diffraction and high-resolution transmission electron microscopy. Strain effects due to lattice mismatch between substrate and film, and between different layers in the heterostructures were found to play a key role in determining the thin film properties. La2/3Ba1/3MnO3 films on SrTiO3 substrates show perfect epitaxy and grow coherently strained over the whole film thickness. In contrast, La2/3Sr1/3MnO3 films on SrTiO3 substrates were found to form two layers with different lattice parameters separated by an intrinsic interface region containing a high density of defects. La2/3Ba1/3MnO3/SrTiO3 superlattices are coherently strained and show a very low density of structural defects and sharp interfaces. The observed interface roughness was below 1 nm allowing the controlled growth of continuous two unit-cell thick La2/3Ba1/3MnO3 layers. We also discuss the influence of strain on the electrical transport properties.