Identification of the misfit dislocations at YBa₂Cu₃O_7-δ/SrTiO₃ interface using moiré fringe contrast

Misfit dislocations at YBa₂Cu₃O_7-δ (YBCO)/SrTiO₃ (STO) interfaces were studied to understand effects which could be responsible for the high interfacial J_c in YBCO thin films. In YBCO films with thickness ranging from 5 to 100 nm, the interfacial structures (e.g. misfit dislocations) of YBCO/STO were investigated using moiré fringe contrast in plan-view transmission electron microscopy (TEM). The observed moiré pattern has a spacing of 17 nm which corresponds to the lattice mismatch between the YBCO a lattice spacing and the cubic STO lattice constant. As the YBCO thickness reaches 100 nm, twin structures dominate the image contrast. Our observations indicate that the moiré pattern originates from the lattice mismatch between the substrate and the orthorhombic phase of YBCO.