Synchrotron X-ray studies of ultra-high-quality crystalline YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// in submicron thick films

The crystal structure of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film grown on SrTiO/sub 3/ substrate was studied by high-resolution X-ray scattering using synchrotron radiation. The films were found to consist of two major components: mosaic aligned grains and an ultra-high-quality single-crystal film. The scattering of the former component gave the normal diffraction pattern and its coherent grain size was determined, by fitting the Bragg reflection profiles, to be 2500 /spl Aring/ (horizontal) and 100 /spl Aring/ (vertical). The signature of the ultra-high-quality film was only observed in low index Bragg reflections. From analysis of the peak profiles, the coherent length of this component was found to be tens of microns (horizontal) and 1800 /spl Aring/ (vertical, the entire film thickness). An exponential strain field was found close to the interface which causes asymmetry in the /spl theta/-2/spl theta/ direction. We also found that the scattering intensity of this single crystal film was affected by the correlated roughnesses on the lattice planes, which replicate from the roughness of the substrate surface during growth. The Debye-Waller like roughness factor quickly diminishes the reflectivity as the diffraction angle (2/spl theta/) increases, which prevents the observation of the ultra-high-quality film at high angle Bragg reflections. Furthermore, our results indicate that 95% of the film volume is occupied by this excellent single-crystal film. It is clear that the superconducting properties of the sample will reflect this high quality film, rather than the 5% mosaic grains. These observations may help to account for the enhanced transport properties of thin film compared to their bulk counterparts.