Atomic-Scale Observation of Moire potential in Twisted Hexagonal Boron Nitride Layers by Electron Microscopy

TL;DR

This study develops a method using electron microscopy to directly observe and reconstruct the moire potential in twisted hexagonal boron nitride layers, revealing the role of atomic overlap in moire pattern formation.

Contribution

The paper introduces a novel approach combining chemical exfoliation and high-resolution electron microscopy to visualize and analyze the moire potential at atomic resolution in MSLs.

Findings

Moiré diffraction spots can be observed in Fourier space.

The moire potential is reconstructed via inverse Fourier transform.

Local atomic overlap influences moire potential distribution.

Abstract

Moire superlattices (MSLs) are an emerging class of two-dimensional functional materials whose electronic states can be tuned by the twist angle between two van der Waals layers and/or the relative placement of the layers. The intriguing properties of MSLs are closely correlated to the moir\'e potential, which is the electrostatic potential induced by interlayer coupling. Intensive efforts have been made to understand the nature and distribution of the moire potential by using various experimental and theoretical techniques. However, the experimental observation of the moir\'e potential is still challenging because of the possible presence of the surface and/or interlayer contaminants. In this work, we develop a method to obtain hexagonal boron nitride (hBN) nanolayers (with or without twist) using a specially designed chemical exfoliation technique. The resulting hBN nanolayers are atomically clean and strain free, hence providing ideal MSLs for the investigation of their moir\'e potential. Aberration-corrected high resolution transmission electron microscopy measurements on the twisted hBN nanolayers allow us to observe moir\'e diffraction spots in Fourier space. Then, the moire potential is reconstructed by the inverse fast Fourier transform of the moire diffraction spots. It has been revealed that the local interlayer atomic overlap plays a decisive role in determining the periodicity and distribution of the moir\'e potential, as supported by density functional theory calculations. This work not only provides a general strategy to observe the moire potential in MSLs, but it also expands the application of electron microscopy to the further study of MSLs with atomic resolution.