(color online) Atomic-scale image of a STO/PZT/STO thin-film heterostructure, recorded along the [ ] direction under the NCSI condition. The horizontal arrows denote the horizontal interfaces between the PZT and the top and the bottom STO film layers. The dotted line traces the 180° domain wall. The arrows of show the directions of the polarization. Insets display magnifications of the dipoles formed by the displacements of ions in the unit cells (yellow: PbO, red: Zr/Ti, blue: O).^[29]