engleski

Molecular Beam Epitaxy And Microstructural Study Of La2-Xsr1+Xcu2o6+Y Thin Films

Thin films of La2SrCu2O6+y with varying Sr/La ratios have been grown by: molecular beam epitaxy on (001) SrTiO3; their structural as well as their transport properties are reported. Under appropriate conditions, thin films with a metal-like resistivity down to 8 K are obtained; i.e., these films are closer to the onset of superconductivity than previous results indicate for bulk samples. This observation might be explained by a: thin-film-specific alteration in site occupation of the La and Sr atoms in the lattice. In addition, the defect structures of a typical sample have been studied by transmission electron microscopy and the thin-film/substrate interface structure is determined. Out-of-phase boundaries with displacement vectors R = [00 1/5] occur throughout the entire film thickness. Such interfaces, which possibly originate at substrate surface steps, disconnect the CuO2 layers and negatively influence eventual superconductivity. The films;contain copper oxide outgrowths and nano-sized a-axis grains at the surface. Locally a 2 root 2a(p) x 2 root 2a(p) modulation is observed; we have determined its unit cell and compared it with other so-called 2 root 2a(p) x 2 root 2a(p) structures occurring in other superconducting compounds such as YBa2Cu3O7-d and Bi1.8Pb0.4Sr2Ca2Cu3O10+x.

copper oxides; superconducting films; transport properties; structural disorder; growth; perovskite; Yba2cu3o7-delta; deposition; oxidation system

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