Formation of dislocations via misfit strain across interfaces in epitaxial heterostructures*

Dislocations often occur in thin films with large misfit strain as a result of strain energy accumulation and can drastically change the physical properties. Here the structure and dislocations in heterostructures with large misfit strain are investigated on atomic scale. When grown on SrTiO₃ (001), the dislocations in both the monolithic BaTiO₃ thin film and its superlattices with SrIrO₃ appear above a critical thickness around 6 nm. The edge component of the dislocations is seen in both cases with the Burgers vector of a<100>. However compared to monolithic BaTiO3 the dislocation density is slightly lower in BaTiO₃/SrIrO₃ superlattices. In this superlattice, when considering the SrTiO₃ lattice constant as the reference, BaTiO₃ has a larger misfit strain comparing with SrIrO₃. It is found that in these two cases, the dislocation formation is only affected by the critical thickness of the film with a larger lattice misfit. It is interesting that a strong octahedral tilt/rotation mismatch at BaTiO₃/SrIrO₃ interface, does not contribute to the creation of dislocations. Our findings show that it is possible to control the position of dislocations, an important step towards defect engineering.