Researchers at South China Normal University have made important progress in the manufacturing of layered low-dimensional single-crystal materials, achieving the controllable growth of rhombohedral phase boron nitride layered single crystals on nickel substrates. The related study was published in Nature on May 2.
Hexagonal boron nitride is a highly promising next-generation low-dimensional dielectric insulating material. The rhombohedral (ABC) stacking layered structure retains the excellent physical and chemical properties of hexagonal boron nitride while exhibiting intrinsic ferroelectric and nonlinear optical properties. The controllable preparation of large-sized ABC stacking layered single crystals is essential for fundamental research and realizing their wide applications. However, the rapid growth of the first layer of boron nitride film on the metal substrate catalytically generates a shielding effect, hindering the continuous growth of subsequent layers.
Furthermore, various stacking layered hexagonal boron nitrides (e.g., ABC, AA'A, and ABA) exhibit good stability, leading to the coexistence of multiple stacking sequences in the same sample. Therefore, the preparation of ABC stacking layered single crystals must be based on stronger interfacial interactions, and the epitaxial substrate surface must be designed to match the atomic configuration of the ABC stacking for uniform growth.
The principle and preparation process of growing multilayer rhombohedral boron nitride single crystals with inclined steps. Image provided by Wei Wenya.
Researchers propose a substrate-based in-plane and out-of-plane synergistic control mechanism to design and prepare high steps with inclined surfaces on a single crystal metal Ni substrate, effectively regulating the growth of layered single crystals. They utilize Ni(520) substrate surface cooling aggregation to form inclined high steps, which can synergistically control and lock the in-plane crystallographic orientation and out-of-plane slip vectors of ABC-stacked hexagonal boron nitride during growth, inducing the nucleation and growth of ABC-stacked crystal domains. Based on this theory, precise ABC atomic layer-stacked rhombohedral boron nitride single crystals were successfully prepared on the Ni(520) surface. Theoretical calculations also demonstrate that the non-centrosymmetric ABC stacking leads to the accumulation of interlayer polarization vectors in the out-of-plane direction, exhibiting ferroelectricity.
Furthermore, the stacked layers have small interlayer slip and polarization reversal barriers, with a theoretical width of ferroelectric domains of only about 10 nanometers, indicating their potential as high-density information storage media. Experimental in-situ transmission electron microscopy observations further confirm that the polarization reversal of ABC-stacked layers originates from interlayer slip. Additionally, based on piezoresponse force microscopy measurements, it was found that ABC-stacked layers exhibit a high Curie temperature, enabling the writing and erasing operations of ferroelectric domains.
The above research was conducted in collaboration by Professor Xu Xiaozhi's team at the School of Physics, South China Normal University, Research Fellow Wei Wenya, Researcher Bai Xuedong's team at the Institute of Physics, Chinese Academy of Sciences, Professor Liu Kaihui's team at Peking University, Researcher Zheng Xiaorui's team at Westlake University, and Professor Ding Feng's team at the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences.
For more information, refer to the related paper: https://doi.org/10.1038/s41586-024-07286-3
