Atomic-scale HAADF-STEM images of polarized head-to-head and tail-to-tail heterointerfaces
Periodic Large Scale Quadruple Vortex Domain Structures in BiFeO3 Thin Films Grown on Orthogonal PrScO3 (110) Substrates (a) dark field image of a planar sample; (b, c) possible distribution of polarization vectors at the domain wall of the four configurations.
The evolution of a1/a2 domains in (a) 22 nm (b) 43 nm (c) 54 nm (d) 86 nm thick PbTiO3 thin films deposited on orthogonal GdScO3 (110) substrates.
(a) The symmetric oxide electrode sandwiches the periodic closed domain structure in the PbTiO3 ferroelectric thin film; (b) The asymmetric oxide electrode sandwiches alternating ac domain structures in the PbTiO3 ferroelectric thin film. Right: Cover article.
Institute of Metal Research, Chinese Academy of Sciences Shenyang Research Institute of Solid State Atomic Images, National Institute of Materials Science, Ma Xiuliang, Zhu Yinlian, Ph.D. Liu Ying, Ph.D., Li Shuang, Ph.D., recent controllable growth and regulation of heterointerfaces and homointerfaces in ferroelectric thin films A series of new developments have been made in the microstructural performance.
Ferroelectric materials have attracted extensive attention due to their rich physical properties and wide application prospects in ferroelectric devices. Due to the demand for miniaturization of electronic devices, ferroelectric materials are often used in research and applications in the form of thin films. As the size of the thin film decreases, the interface problem becomes more and more important. "Interface as a device" is also applicable to oxides. For the ferroelectric thin film, the functional interface includes a homogeneous interface and a heterogeneous interface. The former refers to the interface formed by the same composition and structure in the same ferroelectric material, and is called a ferroelectric domain wall; the latter is two kinds. Interface made of different materials. Ferroelectric domain walls have attracted a great deal of interest due to their novel conductivity and photovoltaic properties. The latter has become a research hotspot due to the strange physical properties resulting from the interaction of lattice, orbit, charge, and spin at the heterojunction interface.
In terms of heterogeneous interfaces, the research team successfully fabricated a BiFeO3/PbTiO3 heterogeneity with polarized head-to-headband positive charge and tail-to-tail band negative charge through a carefully designed thin-film system using atomic-scale pulsed laser growth technology. interface.
This study found that the head-to-head heterointerface has a width of about 5-6 cells, and there is an atomic reconstruction, and the polarization at both sides of the interface is significantly enhanced. Atomic-scale structural and chemical elemental analysis shows that the reconstructed interface is oxygen-rich and can effectively compensate for the positive bound charge generated by the head-to-head polarization. In contrast, the tail-to-tail heterogeneous interface is very well grown epitaxially, with about 3-4 single-cells in the interface layer. It is speculated that oxygen vacancies exist at the interface to shield negative bound charges. The research work discussed the formation mechanism of different interfaces through the viewpoint of charge redistribution. Among them, the controlled growth of heterointerfaces and the study of atomic scales may promote the exploration of their properties and applications in electronic devices. Related research results were published in ACS Applied Materials & Interfaces.
In terms of homogenous interfaces, researchers have made important progress in the study of topological ferroelectric domains in BiFeO3 thin films, topologically closed domains in PbTiO3 thin films, and a1/a2 domain structures. These domain structures are microscopic topological phenomena found in ferroelectric thin films and have significant electrical polarization characteristics.
The research team used the substrate to regulate the strain of the thin film and obtained unique domain structures in tensile strained BiFeO3 multiferroic films and PbTiO3 ferroelectric thin films, respectively. A periodic large-scale four-state vortex domain structure was obtained in a BiFeO3 multiferroic thin film grown on an orthogonal PrScO3(110) substrate; PbTiO3 ferroelectric thin films of different thickness were grown on a perpendicular GdScO3(110) substrate. The periodically distributed a1/a2 domain structure was obtained, and its structural details were further analyzed using aberration-corrected transmission electron microscopy. These findings enriched people's understanding of the domain configuration in ferroelectric thin films and provided a method for effective domain configuration adjustment, controllable preparation of domain configurations in ferroelectric thin films, and related research and potential applications. Provides important information. Related research results were published on Applied Physics Letters and Acta Materialia, respectively.
Closed domain structures have attracted wide attention due to their application prospects in new ferroelectric devices such as data storage devices, spin tunnel junctions, ultra-thin capacitors, and the like. It is generally believed that the oxide electrode can destroy the stability of the closed domain, however, it is inevitable that the ferroelectric film is in contact with the electrode when it is applied to an electronic device. Previous research by the research group showed that closed domains can be stably present in tensile ferroelectric thin films and tensile stress plays a key role in its formation. Based on this, they expect similar phenomena may occur in the PbTiO3 electrode system. Two kinds of oxide electrodes were used in the experiment: one was SrRuO3 electrode and the other was La0.7Sr0.3MnO3 electrode. Studies have shown that when the upper and lower electrodes are symmetrical, the periodic closed domain structure can be stably present in the PbTiO3 film, and when the electrodes are asymmetric, alternating ac domains appear.
This work has overturned the previous belief that electrodes would hinder the formation of closed domains, provided important information for an in-depth understanding of the properties of closed domain structures, and made it possible to study the evolution of this structure under external electric fields. The results of the relevant study were published in a cover article on Applied Physics Letters, which was published on July 31st. At the same time, the AIP Publishing Group was promoted as a major scientific development at the weekly press conference.
This work has been supported by the National Natural Science Foundation of China's key projects and projects, the frontier scientific research projects of the Chinese Academy of Sciences and the "973" project of the Ministry of Science and Technology.
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