# Electron diffraction and dark-field TEM for structural analysis of 2D van der Waals materials

## TL;DR

This paper reviews how electron microscopy techniques help study structural variations in 2D van der Waals materials and their impact on physical properties.

## Contribution

The paper highlights recent advances in combining electron diffraction and dark-field imaging to study structural degrees of freedom in 2D materials.

## Key findings

- Electron diffraction and dark-field TEM reveal structural variations like stacking domains and corrugations.
- These techniques enable real-time observation of structural changes under external stimuli.
- They connect structural evolution directly to functional behavior in 2D van der Waals materials.

## Abstract

Two-dimensional (2D) van der Waals materials possess structural degrees of freedom that set them apart from conventional bulk crystals and strongly influence their physical properties. Such freedom, enabled by the weak interlayer bonding, permits stacking, twisting, and lateral sliding of layers, leading to structural variations such as out-of-plane corrugations, layer-number–dependent electronic and optical responses, and interlayer registry variations that produce stacking domains with distinct functionalities. Capturing and understanding these variations is essential for linking structure to function. Transmission electron microscopy (TEM) offers complementary approaches for this purpose: electron diffraction provides quantitative crystallographic fingerprints, while dark-field (DF) imaging translates selected diffraction information into spatial maps of local structure. When combined, these techniques can resolve complex structural modulations across multiple length scales and under diverse experimental conditions. Recent advances have extended diffraction and DF imaging into in-situ and operando regimes, enabling real-time observation of domain reconfiguration, phase transitions, and polarization switching under external stimuli. This review discusses how these methods are applied to 2D van der Waals materials to reveal structural degrees of freedom and illustrates their unique capability to directly connect structural evolution to functional behavior.