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

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) van der Waals (vdW) ferroelectrics are promising for nano-electronics.
• Group-IV monochalcogenides exhibit strong room-temperature in-plane polarization, even in monolayers.
• Polarization in these materials is sensitive to lattice strain and stacking order.

Purpose of the Study:

• To investigate the interplay between lattice strain, stacking order, and domain properties in vdW SnSe.
• To understand the structural mechanisms governing ferroelectric domain behavior in 2D materials.

Main Methods:

• Utilized four-dimensional scanning transmission electron microscopy (4D-STEM).
• Simultaneously probed in-plane strain and out-of-plane stacking in vdW SnSe.

Main Results:

• Observed significant in-plane lattice strain (up to 4%) with gradients at domain walls, mitigating defect formation.
• Discovered unique ferroelectric-to-antiferroelectric domain walls stabilized by vdW forces.
• Identified potential for anisotropic nonlinear optical responses due to these domain walls.

Conclusions:

• Provided a detailed understanding of the structural factors influencing domain properties in vdW SnSe.
• Established a foundation for engineering domain walls in vdW ferroelectrics for novel electronic and optical applications.