Stacking sequence of YBa 2Cu 3O 7 thin film on SrTiO 3 substrate

Abstract

The interface between substrate SrTiO 3 and thin film YBa 2Cu 3O 7 was studied by high resolution electron microscopy. The atomic stacking sequence was found to be of only one type: bulk-SrO-TiO 2-BaO-CuO 2-Y-CuO 2-BaO-CuO-bulk. Misfit dislocations in the YBa 2Cu 3O 7 film were only found to extend up to the first few unit cells of YBa 2Cu 3O 7 for a straight interface. Frequently, the YBa 2Cu 3O 7 lattice was observed to be shifted parallel to the interface with respect to the lattice of the substrate, which was accompanied by an elongation of the distance between YBa 2Cu 3O 7 and SrTiO 3. This shift results from inserting a misfit dislocation down to the interface near the step of the substrate. On a single unit cell step of SrTiO 3, the YBa 2Cu 3O 7 grows on both the flat surfaces with the same stacking sequence, resulting in a c/3 antiphase boundary at the step. On a large substrate step the YBa 2Cu 3O 7 will grow to form a perfect YBa 2Cu 3O 7 structure, one or two unit cells of YBa 2Cu 3O 7 away from the interface.