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

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 he terostructures were found to play a key role in determining the thin film p roperties. La2/3Ba1/3MnO3 films on SrTiO3 substrates show perfect epitaxy a nd grow coherently strained over the whole film thickness. In contrast, La2 /3Sr1/3MnO3 films on SrTiO3 substrates were found to form two layers with d ifferent lattice parameters separated by an intrinsic interface region cont aining a high density of defects. La2/3Ba1/3MnO3/SrTiO3 superlattices are c oherently strained and show a very low density of structural defects and sh arp interfaces. The observed interface roughness was below 1 nm allowing th e controlled growth of continuous two unit-cell thick La2/3Ba1/3MnO3 layers . We also discuss the influence of strain on the electrical transport prope rties. (C) 2000 Elsevier Science B.V. All rights reserved.