Controlled Growth and Atomic-Scale Mapping of Charged Heterointerfaces in PbTiO₃/BiFeO₃ Bilayers

Functional oxide interfaces have received a great deal of attention owing to their intriguing physical properties induced by the interplay of lattice, orbital, charge, and spin degrees of freedom. Atomic-scale precision growth of the oxide interface opens new corridors to manipulate the correlated features in nanoelectronics devices. Here, we demonstrate that both head-to-head positively charged and tail-to-tail negatively charged BiFeO 3 /PbTiO 3 (BFO/PTO) heterointerfaces were successfully fabricated by designing the BFO/PTO film system deliberately. Aberration-corrected scanning transmission electron microscopic mapping reveals a head-to-head polarization configuration present at the BFO/PTO interface, when the film was deposited directly on a SrTiO 3 (001) substrate. The interfacial atomic structure is reconstructed, and the interfacial width is determined to be 5–6 unit cells. The polarization on both sides of the interface is remarkably enhanced. Atomic-scale structural and chemical element analyses exhibit that the reconstructed interface is rich in oxygen, which effectively compensates for the positive bound charges at the head-to-head polarized BFO/PTO interface. In contrast to the head-to-head polarization configuration, the tail-to-tail BFO/PTO interface exhibits a perfect coherency, when SrRuO 3 was introduced as a buffer layer on the substrates prior to the film growth. The width of this tail-to-tail interface is estimated to be 3–4 unit cells, and oxygen vacancies are supposed to screen the negative polarization bound charge. The formation mechanism of these distinct interfaces was discussed from the perspective of charge redistribution.