# Stacking, Strain, & Twist in 2D Materials Quantified by 3D Electron Diffraction

## TL;DR

This paper introduces a method using 3D electron diffraction in TEM to precisely analyze the 3D structure of 2D materials, revealing detailed stacking, twist, and interlayer parameters that are difficult to measure with traditional techniques.

## Contribution

The study demonstrates a novel approach combining electron diffraction and tilt to quantitatively determine 3D structural parameters of 2D materials with sub-Angstrom accuracy.

## Key findings

- Accurate characterization of multilayer graphene stacking order.
- Determination of interlayer chalcogen-chalcogen spacing as 3.07 +/- 0.11 Å.
- Quick identification of multilayer rhombohedral graphene.

## Abstract

The field of two-dimensional (2D) materials has expanded to multilayered systems where electronic, optical, and mechanical properties change-often dramatically-with stacking order, thickness, twist, and interlayer spacing [1-5]. For transition metal dichalcogenides (TMDs), bond coordination within a single van der Waals layer changes the out-of-plane symmetry that can cause metal-insulator transitions [1, 6] or emergent quantum behavior [7]. Discerning these structural order parameters is often difficult using real-space measurements, however, we show 2D materials have distinct, conspicuous three-dimensional (3D) structure in reciprocal space described by near infinite oscillating Bragg rods. Combining electron diffraction and specimen tilt we probe Bragg rods in all three dimensions to identify multilayer structure with sub-Angstrom precision across several 2D materials-including TMDs (MoS2, TaSe2, TaS2) and multilayer graphene. We demonstrate quantitative determination of key structural parameters such as surface roughness, inter- & intra-layer spacings, stacking order, and interlayer twist using a rudimentary transmission electron microscope (TEM). We accurately characterize the full interlayer stacking order of multilayer graphene (1-, 2-, 6-, 12-layers) as well the intralayer structure of MoS2 and extract a chalcogen-chalcogen layer spacing of 3.07 +/- 0.11 Angstrom. Furthermore, we demonstrate quick identification of multilayer rhombohedral graphene.