Aligning van der Waals heterostructures using electron backscatter diffraction

TL;DR

This paper demonstrates that Electron Backscatter Diffraction (EBSD) can accurately determine the crystallographic orientation of van der Waals materials, enabling precise control of twist angles for advanced electronic and optical applications.

Contribution

It introduces EBSD as a new, precise method for characterizing van der Waals materials' orientations, extending its use beyond bulk materials and enabling twist angle engineering.

Findings

EBSD achieves orientation precision better than 0.2° in van der Waals materials.

EBSD is applicable to various low-symmetry van der Waals crystals.

Controlled twist angles enable observation of novel phonon polaritons.

Abstract

Precise and accurate determination of crystallographic orientation is crucial for engineering van der Waals heterostructures, where the twist angle between layers controls emergent electronic and optical properties. While Electron Backscatter Diffraction (EBSD) has been extensively used for bulk materials, its application to van der Waals materials remains largely unexplored. In this work, we demonstrate EBSD as a robust and versatile tool for determining crystallographic orientations of van der Waals materials with high precision. We show quantitative agreement between EBSD-determined orientations and facet orientations in orthorhombic {\alpha}-MoO3 flakes on silicon substrates. We use Grain Reference Orientation Distribution (GROD) and Kernel Average Misorientation (KAM) across the flakes to demonstrate precision better than 0.2{\deg}. We extend this technique to other low-symmetry materials, specifically, monoclinic {\alpha}-As2Te3, monoclinic GaTe and triclinic ReSe2, demonstrating broad applicability across van der Waals materials with different crystal structures. Finally, as a proof-of-concept application, we leverage EBSD-determined orientations to engineer twisted {\alpha}-MoO3 heterostructure with precisely controlled twist angle, enabling observation of recently reported canalized phonon polaritons. Our results establish EBSD as a powerful characterization method for van der Waals materials, enabling precise orientation control essential for twistronics and twist-optics.