Effect of the two (100) SrTiO3 substrate terminations on the nucleation and growth of YBa2CU3O7-δ 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 termination of the (100) SrTiO3 substrate is expected to influence both the nucleation and the dislocation formation in YBa2Cu3O7-delta (123) films. To investigate this substrate-film interaction, we developed a new ex situ method to prepare SrO-terminated substrates in addition to the well-known TiO2 termination. It is shown that: (i) preferential precipitation occurs when depositing submonolayer 123 films on SrO-terminated SrTiO3 and (ii) such precipitates are absent on the TiO2 termination. It appears that the substrate termination determines both the starting and terminating layer of the 123 phase. Similar effects are observed in submonolayer thick films with cation stoichiometries 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 of threading dislocations does not depend on the substrate termination. (C) 2001 Elsevier Science B.V. All rights reserved.