Effect of Terraces at the Interface on the Structural and Physical Properties of La_0.8Sr_0.2MnO_3 Thin Films

  • Employing atomic force microscopy, transmission electron microscopy and the second harmonic generation technique, we carefully explore the structural properties of 6-unit-cell-thick La_0.8Sr_0.2MnO_3 films grown on SrTiO_3 with atomically flat TiO_2-terminated terraces on the surface. The results clearly demonstrate that the terraces on the surface of TiO_2-terminated SrTiO_3 can improve the layer-by-layer epitaxial growth of the manganite films, which results in uniform film coverage at the beginning of growth and thus reduces the substrate-induced disorder at or near the interface. Comparing the magnetic and transport properties of La_0.8Sr_0.2MnO_3 films with the thicknesses varying from 6 unit cells to 80 unit cells grown respectively on as-received SrTiO_3 and TiO_2-terminated SrTiO_3, it is found that these atomically flat terraces on the surface of TiO_2-terminated SrTiO_3 can greatly enhance the Curie temperature and conductivities of the ultrathin La_0.8Sr_0.2MnO_3 films with thickness less than 50 unit cells, while no obvious difference is detected in the magnetic and transport properties of the 80 unit-cell thick films.
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