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We present the results of collaboration between the groups of Naples and Genoa Universities/INFM, focused on thin films superconducting borocarbides. In particular a careful study of the deposition of non-magnetic LuNi[sub 2]B[sub 2]C thin films by Pulsed Laser Deposition (PLD) on MgO and other substrates will be presented. While samples with good c-orientation and superconducting properties are obtained in a wide range of deposition parameters, in-plane micrometric oriented structures are obtained only in a narrow range of conditions, as evidenced by X-rays measurements and AFM (atomic force microscopy) analyses. A special set-up for the in situ interchanging of shadow masks has been developed in order to deposit the different patterned layers and different buffer and/or barrier layers. New results on the temperature dependence of the LuNi[sub 2]B[sub 2]C gap using S/N contact junctions are presented and discussed. The obtained value of the superconducting gap and its temperature dependence agrees very well with the BCS prediction. We present also microwave measurements of the surface impedance performed on large area films obtained by sputtering technique on low loss sapphire substrates. The data confirm the overall BCS-like behavior of these compounds. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the effect of thickness on the structure and superconductivity of Nd1.2Ba1.8Cu3O7+x (NdBCO) epitaxial films deposited on SrTiO3 (100) substrates. High quality NdBCO films were deposited by high oxygen pressure sputtering. The samples have been carefully characterized by transport measurements and X-ray diffraction using conventional and synchrotron radiation sources. Two structural transformations are observed. The first one is a crossover from the orthorhombic and twinned structure, typical of thick samples, to a pseudotetragonal phase at thickness lower than 60 unit cells. The pseudotetragonal phase exhibits peculiar X-ray diffuse scattering around the Bragg reflections, associated to nanostructured twinned domains. The second one appears at thickness lower than 20 unit cells and is assigned to a pseudotetragonal–tetragonal transition. The transport properties are not modified at the first crossover, while a substantial decrease of T c and of the number of holes is observed at the pseudotetragonal–tetragonal transformation. Our results suggest that the structural rearrangement and the transport properties are explained by the ordering of Cu(1)O chains. [Copyright &y& Elsevier]

Superconductivity of Y1Ba2Cu3O7-d c-axis epitaxial films is always depressed when the films thickness is reduced to few unit cells. Here we report a detailed study of the structure, morphology and transport properties of Y(Nd0.05Ba1.95)Cu3O7-d films deposited by high pressure diode oxygen sputtering. Films having thickness between 9 and 250 unit cells deposited on LaAlO3 substrates have been investigated. It is shown that both Tc and Jc are reduced by decreasing the film thickness. The effect is quite evident even in relatively thick Y(Nd0.05Ba1.95)Cu3O7-d films made of 32 unit cells. Moreover it is shown that the a and b axes of the films approach one to each other with decreasing thickness. A nine unit cell film is almost tetragonal. Application of a simple elasticity theory to account for the structural changes fails to explain the experimental results. Inelastic strain induced by an oxygen disordering in the Cu(1)–O chains may explain the experimental results. [Copyright &y& Elsevier]