Improved structural properties and surface morphology of Nd1+xBa2-xCu3O7-δ thin films deposited by d.c. magnetron sputtering

We report the fabrication of very smooth NdBCO thin films deposited by d.c. magnetron sputtering using Nd rich target (EDS composition Nd1.12BaL88CU3O7-delta). Films characterized by critical temperature (R=0) higher than 90 Ii and maximum roughness lower than 2-3 nm on large areas are routinely obtained on SrTiO3 non-vicinal substrates. STM studies performed in situ in UHV environment, show a 2D nucleation mechanism of the growth preserved up to a thickness higher than 100 nm. This is in contrast to the common observation of screw dislocations starting from 10-12 nm in c-asis ReBCO thin films, that gives rise to an increase of the roughness with thickness. We compare the growth modes, the superconducting, and the structural properties of our NdBCO thin films deposited by d.c. magnetron sputtering from stoichiometric and Nd-rich targets, on different kind of substrates. The experimental results are discussed in the framework of the role of Nd/Ba substitution in the properties of Nd1+xBa2-xCu3O7-delta thin films.