Effect of Terraces at the Interface on the Structural and Physical Properties of La_0.8Sr_0.2MnO₃ 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_0.2MnO₃ films grown on SrTiO₃ with atomically flat TiO₂-terminated terraces on the surface. The results clearly demonstrate that the terraces on the surface of TiO₂-terminated SrTiO₃ 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_0.2MnO₃ films with the thicknesses varying from 6 unit cells to 80 unit cells grown respectively on as-received SrTiO₃ and TiO₂-terminated SrTiO₃, it is found that these atomically flat terraces on the surface of TiO₂-terminated SrTiO₃ can greatly enhance the Curie temperature and conductivities of the ultrathin La_0.8Sr_0.2MnO₃ 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.