The Flexible Magnetic-Electronic Materials and Devices Group from the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS) has proposed a novel strategy to precisely manipulate interlayer stacking orders and related properties in two-dimensional (2D) van der Waals layered materials via mechanical bending, enabling efficient electric polarization switching. 

This work was published in Physical Review Letters.

2D van der Waals materials have garnered significant attention in flexible electronics due to their exceptional conformal adaptability and good mechanical flexibility.

Composed of atomically thin layers, 2D materials possess a unique interlayer stacking degree of freedom. Through modifying the stacking order, diverse phases can be achieved, unlocking extraordinary electrical, optical, and magnetic properties.

However, precisely controlling stacking orders in 2D materials is challenging — it requires overcoming energy barriers for interlayer sliding, thus limiting practical applications.

Researchers at NIMTE proposed an innovative mechanical bending approach for dynamically controlling stacking orders and associated optical, topological, electronic, and magnetic properties in 2D materials.

By virtue of artificial intelligence (AI)-assisted machine-learning potentials, large-scale atomic simulations revealed that mechanical bending generates irreversible kinks in bent bilayers, like h-BN, MoS₂, and nonferroelectric bilayer graphene. This kink formation originates from the interplay between the interlayer stacking energy and bending energy.

Meanwhile, continuous interlayer sliding occurs during bending due to the high in-plane rigidity of 2D materials. Through atomic relaxation, three optimized bilayer structures with distinct bending angles have been achieved, forming domain walls of different types. 

Notably, bending-induced sliding induces the interlayer charge transfer, which can reverse the electric polarization.

Since the stacking order plays a crucial role in material property modulation, the mechanism of bending-induced interlayer sliding can be applied to “sliding flexo-responsesvan der Waals”, including sliding flexomagnetic, sliding flexo-photovolataic, and sliding flex-ovalleytronic effects, opening new avenues for designing next-generation flexible electronics.

This work was supported by the National Key R&D Program of China (Grants Nos. 2022YFA1403000 and  2021YFA0718900), the National Nature Science Foundation of China (Grants Nos. 12204496, 12304049 and 51931011), the Zhejiang Provincial Natural Science Foundation (Grant No. Q23A040003), and Ningbo Nature Science Foundation (No. 2023J360).

Atomic configurations and polarization textures in bent bilayer h-BN (Image by NIMTE)

Contact
HE Ri
Ningbo Institute of Materials Technology and Engineering
E-mail: heri@nimte.ac.cn