Domain-dependent strain and stacking in two-dimensional van der Waals ferroelectrics

• Published in: Nature communications 2023-11, Vol.14 (1), p.7168-7168, Article 7168
• Main Authors: Shi, Chuqiao, Mao, Nannan, Zhang, Kena, Zhang, Tianyi, Chiu, Ming-Hui, Ashen, Kenna, Wang, Bo, Tang, Xiuyu, Guo, Galio, Lei, Shiming, Chen, Longqing, Cao, Ye, Qian, Xiaofeng, Kong, Jing, Han, Yimo
• Format: Article
• Language: English
• Subjects: 147/28; 639/301/119/996; 639/301/357/1018; Computer engineering; Electrons; Ferroelectric materials; Ferroelectricity; Ferroelectrics; Humanities and Social Sciences; Materials science; multidisciplinary; Phase transitions; Science; Science & Technology - Other Topics; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-42947-3

Van der Waals (vdW) ferroelectrics have attracted significant attention for their potential in next-generation nano-electronics. Two-dimensional (2D) group-IV monochalcogenides have emerged as a promising candidate due to their strong room temperature in-plane polarization down to a monolayer limit. However, their polarization is strongly coupled with the lattice strain and stacking orders, which impact their electronic properties. Here, we utilize four-dimensional scanning transmission electron microscopy (4D-STEM) to simultaneously probe the in-plane strain and out-of-plane stacking in vdW SnSe. Specifically, we observe large lattice strain up to 4% with a gradient across ~50 nm to compensate lattice mismatch at domain walls, mitigating defects initiation. Additionally, we discover the unusual ferroelectric-to-antiferroelectric domain walls stabilized by vdW force and may lead to anisotropic nonlinear optical responses. Our findings provide a comprehensive understanding of in-plane and out-of-plane structures affecting domain properties in vdW SnSe, laying the foundation for domain wall engineering in vdW ferroelectrics. Van der Waals ferroelectrics hold promising potential as electronic materials. Here, the authors have pioneered an electron microscopy technique to unveil both in-plane and out-of-plane structures critical to their switching behavior, providing valuable insights into potential device applications. (298 in total)