The effect of MgO substrate roughness on YBa2Cu3O7-δ thin film properties

We have investigated the effect of surface roughness of 'as-received' polished, single crystal (001) MgO substrates, from a range of commercial suppliers, on the physical properties of epitaxially-grown high-temperature superconducting YBa2Cu3O7-delta (YBCO) thin films. In particular, we are interested in the effect of polishing grooves, present to some degree in nearly all commercially available substrates, on the transport properties of YBCO films. We have found that for substrate surfaces, which exceeded 1.6 nm roughness the film critical current densities, J(c), were 2-3 times smaller than for films deposited on substrates with a surface roughness less than 1.0 nm. Physical analysis of the YBCO films using X-ray diffraction revealed a correlation between the width and relative intensity of the YBCO (006) peak and film J(c) which appears to be related to the film roughness and hence the underlying MgO roughness. (C) 2003 Elsevier Science B.V. All rights reserved.