Epitaxial growth and properties of YBaCuO thin films

The growth quality of YBaCuO thin films deposited by sputtering on different substrates (Al₂O₃, MgO, SrTiO₃, Zr(Y)O₂) has been studied by X-ray diffraction and channeling experiments as a function of the deposition temperature. Besides the substrate orientation, the substrate temperature is the parameter determining whether films grow in c, a, (110) or mixed directions. Epitaxial growth correlates with high critical current values in the films of up to 5.5 × 10⁶ A/cm² at 77 K. Ultrathin films with thicknesses down to 2 nm were grown revealing three-dimensional superconducting behaviour. Films on (100) SrTiO₃ of 9 nm thickness and below are partially strained indicating commensurate growth. From the analysis of the surface disorder 0.5 displaced Ba atom per Ba₂Y row was obtained indicating that the disordered layer thickness is about 0.3 nm. Tunnel junctions fabricated on these films reveal gap-like structures near ±16 mV and ± 30 mV.