Effect of the two (100) SrTiO3 substrate terminations on the nucleation and growth of YBa2CU3O7-delta thin films

Recently, threading dislocations were identified as the origin of the high critical currents in YBa2Cu3O7-delta films [Nature (Lond.) 399 (1999) 439]. As these dislocations originate at the substrate-film interface, the termi nation of the (100) SrTiO3 substrate is expected to influence both the nucl eation and the dislocation formation in YBa2Cu3O7-delta (123) films. To inv estigate this substrate-film interaction, we developed a new ex situ method to prepare SrO-terminated substrates in addition to the well-known TiO2 te rmination. It is shown that: (i) preferential precipitation occurs when dep ositing submonolayer 123 films on SrO-terminated SrTiO3 and (ii) such preci pitates are absent on the TiO2 termination. It appears that the substrate t ermination determines both the starting and terminating layer of the 123 ph ase. Similar effects are observed in submonolayer thick films with cation s toichiometries 122, 124 and 133. When growing several 123 monolayers on SrO -terminated substrates, no precipitates are formed. Instead, to incorporate the off stoichiometry, defects are introduced. Surprisingly, the density o f threading dislocations does not depend on the substrate termination. (C) 2001 Elsevier Science B.V. All rights reserved.