Observation of screw dislocations in sputtered YBa₂Cu₃O_7-δ films

By imaging the as-grown surfaces of sputtered YBa2Cu3O7-δ films with scanning tunneling microscopy (STM), we have directly observed spiral-shaped growth terraces that emanate from screw dislocations. This surface morphology has important implications for Josephson junctions and superlattices. The density of screw dislocations observed is in the range of 109 cm-2. In addition to their importance as flux pinning sites, these screw dislocations act as growth centers by continually providing a growth step for the attachment of incident species by a step-propagation growth mechanism known as screw dislocation mediated growth. Growth parameters strongly influence the screw dislocation density: it decreases with increasing growth temperature, decreasing growth rate, and increasing substrate misorientation for SrTiO3 surface orientations near {100}. © 1991.