Effect of the two (1 0 0) SrTiO3 substrate terminations on the nucleation and growth of YBa2Cu3O7−δ thin films

Abstract

Recently, threading dislocations were identified as the origin of the high critical currents in YBa2Cu3O7−δ films [Nature (Lond.) 399 (1999) 439]. As these dislocations originate at the substrate–film interface, the termination of the (1 0 0) SrTiO3 substrate is expected to influence both the nucleation and the dislocation formation in YBa2Cu3O7−δ (1 2 3) 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 1 2 3 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 1 2 3 phase. Similar effects are observed in submonolayer thick films with cation stoichiometries of 1 2 2, 1 2 4 and 1 3 3. When growing several 1 2 3 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.