Growth mode selection and transport properties in Nd1Ba2Cu3O7 superconducting films deposited by high oxygen pressure diode sputtering

In this paper we report on the growth mode selection in epitaxial high critical temperature Nd1+xBa2-xCu3O7 (NdBCO) films. The samples have been deposited on (100) SrTiO3 single crystals by high oxygen pressure diode sputtering using a Nd0.97Ba2.03Cu3O7 polycrystalline target. The effect of different deposition parameters on the morphology, superconductivity and structure has been investigated by atomic force microscopy, resistivity and inductive measurements, and x-ray diffraction respectively. While the deposition temperature and oxygen pressure mainly affect the critical temperature of the samples, the surface morphology is strongly dependent on the target-substrate distance. Films realized in identical deposition conditions, i.e. oxygen pressure, rate and substrate temperature, exhibit different growth modes associated with a 10% change of the target-substrate distance. The typical surface roughness of 110 nm thick NdBCO films deposited on SrTiO3 substrates is 1.0 nm (rms) on 5 x 5 μm2 areas. Surprisingly, the critical current density and its temperature dependence are found to be independent of the surface morphology of the films investigated, and are well described by strong pinning provided by large linear defects