Transmission electron microscopy of La_0.67Sr_0.33MnO₃/SrTiO₃/La _0.67Sr_0.33 MnO₃ heterostructures grown by pulsed laser deposition on (001) SrTiO₃

We have analysed by cross-section transmission electron microscopy (XTEM) La_0.67Sr_0.33MnO₃/SrTiO₃/La _0.67Sr_0.33MnO₃ tunnel junctions epitaxially grown on (001) SrTiO₃ by pulsed laser deposition (PLD). La_0.67Sr_0.33MnO₃ (LSMO) is rhombohedral in bulk (pseudo-cubic with an angle of 89.76°); its epitaxy on SrTiO₃ raises two kinds of questions: (1) are the interfaces chemically abrupt? And (2) is the LSMO strained to a tetragonal phase that would fit the cubic substrate? In the present paper, we show, using high-resolution TEM (HRTEM) micrographs and a semi-quantitative technique based on Chemical Mapping (A. Ourmazd et al., Ultramicroscopy 34 (1990) 237) that the extent of roughness or interdiffusion at the interfaces is less than a single unit cell. On the other hand, we deduce from electron diffraction that the LSMO films are at least partially relaxed.