Observation of small interfacial strains in YBa2Cu3Ox sub-micron-thick films grown on SrTiO3 substrates

We have observed x-ray intensity oscillation fringes around low index Bragg reflections in a YBa2Cu3Ox (YBCO) thin film. By employing a combination of crystal truncation rod interference fringe measurements and x-ray reflectivity using synchrotron radiation, we have been able to probe the structures of highly oriented [001] YBCO grown on [001] SrTiO3 substrates. The results demonstrate the presence of a thin disordered surface layer, the excellent coherence between the YBCO surface and the film-substrate interface, the presence of a small (3.2×10−4) interfacial strain existing in the YBCO film. This strain exists close to the film-substrate interface and extends approximately 300 Å into the micron-thick film. Our results demonstrate that high quality detailed information can be obtained, nondestructively, from thin film superconductors of thicknesses typically used for microwave and other applications.