Electron energy-loss spectroscopy study of a (LaMnO3)(8)(SrMnO3)(4) heterostructure

An epitaxially grown heterostructure consisting of alternating layers of La MnO3 (8 unit cells) and SrMnO3 (4 unit cells) on a SrTiO3 substrate has bee n studied by a combination of electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM) on an atomic scale . Excitation edges of all elements are captured with subnanometer spatial a ccuracy, and parametrized to obtain chemical profiles. The fine-edge struct ure of O K and Mn L-2,L-3 edges are interpreted as signatures of the local electronic structure and show a spatial modulation of the concentration of holes with O 2p character. The chemical concentration is found to be differ ent for the bottom and top interface of a SrMnO3 layer. HRTEM complements t he EELS results and confirms the asymmetry of the interfaces. (C) 2001 Amer ican Institute of Physics.