Crystalline quality analysis of YBaCuO ultrathin films by high resolution ion backscattering and channeling spectrometry

Medium energy ion scattering combined with channeling was applied to study the crystalline quality of ultrathin YBaCuO films on (100) SrTiO3 and MgO substrates. Films with thicknesses between 3 and 6 nm were deposited by inverted cylindrical magnetron sputtering. Under optimized growth conditions c-axis oriented growth was obtained with minimum yield values of 2%–12% (depending on thickness) for films on SrTiO3 and 23% on MgO. On the surface of the films a disordered region with a thickness of about 0.6 nm independent of substrate, film thickness, and storage time under ambient conditions was observed. During etching experiments an Y-oxide layer was formed on the surface. For films on SrTiO3 at thicknesses above 4 nm an abrupt increase in the minimum yield was found indicating pseudomorphic growth up to this thickness. In contrast, for films on MgO it was found that a critical film thickness of about 3.6 nm is necessary for the formation of a homogeneous film.