In situ TEM study of polar domain dynamics in 2D ferroelectrics

Recently, ferroelectricity is found to exist in non-polar van der Waals materials if the individual layers are stacked in a way that breaks the inversion symmetry of the crystal. This so-called sliding ferroelectricity has generated significant interest due to the flexibility of inducing ferroelectricity in a vast number of non-polar 2D materials and the potential of realizing novel electronic functionalities [1]. In this study, we use operando transmission electron microscopy (TEM) to study the polar domain dynamics and switching behavior under an external electric field in various parallel-stacked (which breaks the inversion symmetry) and twisted bilayer transition metal dichalcogenides (TMDs) such as MoS₂ and WS₂. Operando TEM allows us to directly visualize the polar domain structures and track the domain dynamics in real time. To fabricate 2D ferroelectric samples, we take CVD-grown monolayer TMD flakes and use the well-established tear-and-stack method to assemble bilayer TMD heterostructures with small twist angles. The twisted bilayer TMD stack is encapsulated with multilayer hexagonal boron nitride and the stack is further capped with top and bottom graphite flakes for electrical contacts. The final stack is then transferred onto a Protochips electrical e-chip and studied under TEM. This study aims to study the impact of dopants and defects to the polar domain dynamics in 2D heterostructures with ferroelectricity.

References:

1. M. V. Winkle et al., Nature Nanotechnology (2024).