Growth Mechanism of Sputtered Films of YBa 2 Cu 3 O 7 Studied by Scanning Tunneling Microscopy

The surface microstructures of c -axis-oriented films of YBa 2 Cu 3 O 7 , deposited by off-axis magnetron sputtering on MgO and SrTiO 3 single crystal (100) substrates, have been investigated with scanning tunneling microscopy and atomic force microscopy. There is strong evidence that the films nucleate as islands and grow by adding material to the edge of a spirally rising step. This results in columnar grains, each of which contains a screw dislocation at its center. This microstructure may be of significance in determining superconducting properties such as critical current, and represents a significant difference between thin films (especially those grown in situ) and bulk materials.