Author:

Keywords:

COPPER OXIDES, SUPERCONDUCTING FILMS, TRANSPORT-PROPERTIES, STRUCTURAL DISORDER, GROWTH, PEROVSKITE, YBA2CU3O7-DELTA, DEPOSITION, OXIDATION, SYSTEM, Science & Technology, Technology, Physical Sciences, Materials Science, Multidisciplinary, Physics, Applied, Physics, Condensed Matter, Materials Science, Physics, 02 Physical Sciences, 03 Chemical Sciences, 09 Engineering, Fluids & Plasmas, 34 Chemical sciences, 40 Engineering, 51 Physical sciences

Abstract:

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.