Electron Channelling Contrast SEM Imaging of Twist Domains in Transition Metal Dichalcogenide Heterostructures

TL;DR

This paper introduces a simple, non-destructive SEM-based imaging method to visualize twist domains in transition metal dichalcogenide heterostructures, enabling detailed analysis of their local reconstructed architecture.

Contribution

It presents a widely accessible electron channelling contrast imaging technique in SEM for visualizing twist domains in TMD heterostructures, compatible with various substrates and encapsulation layers.

Findings

ECCI provides clear visualization of twist domains in TMD heterostructures.

Contrast depends on scattering angles and sample tilt, with optimal imaging conditions identified.

The method is non-destructive and compatible with standard substrates.

Abstract

Twisted 2D material heterostructures provide an exciting platform for investigating new fundamental physical phenomena. Many of the most interesting behaviours emerge at small twist angles, where the materials reconstruct to form areas of perfectly stacked crystal separated by partial dislocations. However, understanding the properties of these systems is often impossible without correlative imaging of their local reconstructed domain architecture, which exhibits random variations due to disorder and contamination. Here we demonstrate a simple and widely accessible route to visualise domains in as-produced twisted transition metal dichalcogenide (TMD) heterostructures using electron channelling contrast imaging (ECCI) in the scanning electron microscope (SEM). This non-destructive approach is compatible with conventional substrates and allows domains to be visualised even when sealed beneath an encapsulation layer. Complementary theoretical calculations reveal how a combination of elastic and inelastic scattering leads to contrast inversions at specified detector scattering angles and sample tilts. We demonstrate that optimal domain contrast is therefore achieved by maximising signal collection while avoiding contrast inversion conditions.