Properties of YBa2Cu3O7 thin films deposited on substrates and bicrystals with vicinal offcut and realization of high IcRn junctions

The surface morphology, microstructure and transport properties of epitaxial YBa₂Cu₃O₇ and PrBa₂Cu₃O₇ thin films and heterostructures deposited on slightly vicinal substrates of SrTiO₃ by high pressure oxygen sputtering were studied. The vicinal angles of the substrates and bicrystals were less then 13°. Depending on the tilt angle of the substrate a transition from spiral or island to step-flow growth leading to an improvement of the surface roughness was observed. Atomic force and transmission electron microscopy were used for these investigations. Furthermore, electrical and structural properties of YBa₂Cu₃O₇ thin films on vicinal offcut SrTiO₃ bicrystals with different grain boundary types were studied. This included junctions with a 2×12° tilt or twist of the YBa₂Cu₃O₇ c-axis across the grain boundary. In comparison to conventional [001]-tilt grain boundaries bicrystal Josephson junctions [100]-tilt grain boundaries showed high I _cR_n-products of up to 1.2 meV at 77 K and up to 8 meV at 4.2 K. IV-curve instabilities, probably of magnetic origin due to flux flow in the electrodes, often could be observed for junctions biased with high current densities