Figure 1. Displacement corrected transmission electron microscopy analysis of PTO / STO multilayer films with adjacent PTO layer thickness ratios of 1. The periodic V-domain arrays appear in each PTO layer and also exhibit periodicity in the direction of the vertical film (Ac) Low magnification TEM bright field image (a), electron diffraction spectrum (b), and high magnification HAADF-STEM image (c) for the PTO / STO multilayers; (df) In-plane lattice strain (d), out-of-plane lattice strain (e) and in-plane lattice rotation (f) two-dimensional distribution obtained by phase analysis.
Figure 2. Displacement corrected transmission electron microscopy analysis of PTO / STO multilayer films with adjacent PTO layer thickness ratio of 0.5. Periodic V-domain arrays occur in the thicker PTO layer, whereas in thinner PTO layers (A) TEM bright field images of PTO / STO multilayers. (B) HAADF-STEM images of thin films. (C, d) The surface obtained by geometric phase analysis of (b) (E, f) corresponds to the two-dimensional distribution of out-of-plane and in-plane lattice rotations in (b). (G, h) A thin PTO layer magnifies the HAADF- STEM like.
Figure 3. The superposition of the polarization vector and the original image clearly shows a flux-fully closed ferroelectric domain with symmetry.
Figure 4. Schematic (ab) and error-induced strain analysis (cf) of the V and H domain arrays (c) Lattice strain diagrams in vertical and (d) horizontal fully closed domain structures. Periodically vertical full closure favors accommodating the strain at the same thickness (f) When the thickness ratio of adjacent PTO layers is 1/2, the formation of a horizontal full closure in the thinner PTO layer facilitates accommodating the strain therein.
Figure 5. Phase field simulation of a multi-layer PTO / STO thin film system. (A) Phase diagram of domain structures in PTO with varying thickness ratios in adjacent PTO layers. There are four domain regions, I, II, III, IV (A), trapezoidal a domain (T), horizontal fully closed domain structure (H), and vertically fully closed domain structure (V), respectively (b) H and T domains near the second transition point (C) Difference in energy density between the V and H domains near the third transition point The domain configurations and their elasticity of the T domains (d, e) and H domains (f, g) Energy Density Distribution. The domain configurations of H domains (h, i) and V domains (j, k) and their elastic energy density distributions.
Institute of Metal Research, Chinese Academy of Sciences Shenyang Institute of Materials Science (Joint) Laboratory Researcher at the Department of Solid Atomic Imaging Ma Xiuliang, Zhu Yinlian and other scientists in the United States, the flux fully closed ferroelectric periodic array and its controllable growth made new progress , The formation of two-dimensional periodic array of flux-closed ferroelectric phase formation phase diagram, and to obtain a clear atomic structure map.
Topological defects have unique properties such as force, electricity and magnetism, which have important application value in electronic devices.As an important topological defect, closed-polarized distribution of ferroelectric vortex domains or full-closed flux domain configurations , And has a bright future in high-density data storage.Because the use of fully closed flux structure to store data can avoid the interaction between the data, so if this nano-domain configuration can be prepared into a periodic array, there will be Conducive to data addressing.
Shenyang Materials Science National (Joint) Laboratory Solid Atomic Imaging Research Materials Interface Electron Microscopy Research team and the Shenzhen Institute of Advanced Technology Chinese Academy of Sciences, Washington University Professor Li Jiangyu, the United States St. Louis University Dr. Li Zhihao, the use of aberration correction transmission Electron microscopy and phase field simulation are used to make progress in the study of two-dimensional periodic closed domains.On the basis of the one-dimensional periodic full-closed domain found in the early stage of the research team, by controlling the three-dimensional strain state, A two-dimensionally ordered flux-fully-closed array was prepared and phase diagrams were constructed by phase-field simulation to predict the existence of two-dimensionally ordered fully-closed arrays.The results of the study were published online Nov. 16, "on.
Strain has a significant impact on the functional properties and microstructure of functional oxides, especially for ferroelectric materials. In their previous work, the research team investigated the effects of two-dimensional strain states (by choosing to provide tensile strain in both directions GdScO3 substrate), a one-dimensional periodic array of vertically closed domains (V-domains) with 180 ° domain walls along the vertical interface was found in the PbTiO3 / SrTiO3 (PTO / STO) Based on which the PTO / STO multi-layer film with thickness modulation is designed and prepared based on the giant strain-induced strain characteristics of the fully closed domain in the tetragonal ferroelectrics. The in-plane strain of the film is modulated by the substrate, and the out-of-plane strain is also effectively controlled, that is, the entire film is in a three-dimensional strain state. The aberration corrected transmission electron microscopy analysis shows that when the thickness of adjacent PTO layers is the same, The fully closed domains (V-domains) along the vertical direction of the walls are periodically arranged in-plane in the vertical direction and periodically in the out-of-plane direction to form two-dimensionally periodic V-domain arrays. When the thickness ratio of adjacent PTO layers At 0.5, the thicker PTO layer remains Periodic V-domain arrays, while the symmetric fully closed domain configuration (H domain) along the horizontal direction of regular 180 ° domain walls appears in the thin PTO layer, resulting in the regular full-closure of H domains and V domains Domain array.
On the basis of aberration-corrected electron microscopy, researchers make phase field simulations by changing the thickness ratio of adjacent PTO layers. From the standpoint of elastic energy, electrostatic energy, energy gradient and other energies competing with each other, The phase diagram of the domain structure of the system with the thickness ratio evolution was obtained.The prediction results based on the phase field simulation obtained the verification of a large number of experimental data in this work.
The research results further improve the importance and effectiveness of domain structure and physical properties of ferroelectric materials through strain control, provide a new way to explore high-density information storage based on ferroelectric materials, which is important for the design and development of novel nanodevices significance.
The research has been funded by the National Natural Science Foundation of China, the CAS Key Research Program of Frontier Science and the State Key Basic Research Development Program (973 Program).
