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

Moiré superlattices (MSLs) are an emerging class of two-dimensional 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. As the twist angle increases (decreases), the resulting MSLs tend to have a shorter (longer) wavelength pattern with in general incommensurate (com-mensurate) patterns, forming an underlying moiré potential depending on the twist angle. Irrespective of the commensura-bility/ incommensurability of MSLs, atomic-scale observation of the moiré potential is quite challenging, and the details of their interlayer interactions and the related anomalous effects such as correlated superconductivity and anomalous quan-tum Hall effects are still elusive. In this work, we show that aberration-corrected transmission electron microscopy allows us to obtain atomic-scale image of the moiré potentials both in the commensurate and incommensurate states. For this pur-pose, we use atomically clean and strain-free hexagonal boron nitride nanolayers, which are fabricated by a chemical exfo-liation method developed especially in this work. Even in the case of incommensurate state, the local interlayer atomic overlap plays a decisive role in determining the resulting moiré potentials, as supported by density functional theory calcu-lations. This work not only provides a general strategy to observe the moiré potential in MSLs, but it also expands the ap-plication of electron microcopy to the further study of MSLs with atomic resolution.