Twist Angle-Dependent Atomic Reconstruction and Moiré Patterns in Transition Metal Dichalcogenide Heterostructures
Matthew R. Rosenberger, Hsun-Jen Chuang, Vladimir P. Oleshko, Madeleine Phillips, Kathleen M. McCreary, Saujan V. Sivaram, C. Stephen Hellberg, Berend T. Jonker
Van der Waals layered materials, such as the transition metal dichalcogenides (TMDs), are an exciting class of materials with weak interlayer bonding which enables one to create so-called van der Waals heterostructures (vdWH). One promising attribute of vdWH is the ability to rotate the layers at arbitrary azimuthal angles relative to one another. Recent work has shown that control of the twist angle between layers can have a dramatic effect on vdWH properties, including the appearance of superconductivity, emergent electronic states,and unique optoelectronic behavior. For TMD vdWH, twist angle has been treated solely through the use of rigid-lattice moiré patterns. No atomic reconstruction, i.e. any rearrangement of atoms within the individual layers, has been reported experimentally to date. However, any atomic level reconstruction can be expected to have a significant impact on the band structure and all measured properties, and its existence will fundamentally change our understanding and theoretical treatment of such systems. Here we demonstrate that vdWHs of MoSe2/WSe2 and MoS2/WS2 at twist angles ≤ 1 degree undergo significant atomic level reconstruction leading to discrete commensurate domains divided by narrow domain walls, rather than a smoothly varying rigid-lattice moiré pattern as has been assumed in prior work. Using conductive atomic force microscopy and transmission electron microscopy, we show that the stacking orientation of the two TMD crystals has a profound impact on the atomic reconstruction, consistent with recent theoretical work on graphene/graphene and MoS2/MoS2 structures at small angular misalignments10 and experimental work on graphene bilayers and hBN/graphene heterostructures. Transmission electron microscopy demonstrates the transition between a rigid-lattice moiré pattern for large angles and atomic reconstruction for small angles.