Rotational and dilational reconstruction in transition metal dichalcogenide moiré bilayers

• Published in: Nature communications 2023-05, Vol.14 (1), p.2989-2989, Article 2989
• Main Authors: Van Winkle, Madeline, Craig, Isaac M., Carr, Stephen, Dandu, Medha, Bustillo, Karen C., Ciston, Jim, Ophus, Colin, Taniguchi, Takashi, Watanabe, Kenji, Raja, Archana, Griffin, Sinéad M., Bediako, D. Kwabena
• Format: Article
• Language: English
• Subjects: 639/301/357/1018; 639/766/119/1000/1018; 639/925/357/537; 639/925/930/2735; Accumulation; ATOMIC AND MOLECULAR PHYSICS; Bilayers; Chalcogenides; Deformation mechanisms; Electronic properties; Electronic structure; Electrons; Humanities and Social Sciences; Image reconstruction; Interferometry; Interlayers; Lattice parameters; Mechanical properties; Molybdenum disulfide; multidisciplinary; Scanning electron microscopy; Scanning transmission electron microscopy; Science; Science (multidisciplinary); Strain; Superlattices; Transition metal compounds; Transmission electron microscopy
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-38504-7

Lattice reconstruction and corresponding strain accumulation plays a key role in defining the electronic structure of two-dimensional moiré superlattices, including those of transition metal dichalcogenides (TMDs). Imaging of TMD moirés has so far provided a qualitative understanding of this relaxation process in terms of interlayer stacking energy, while models of the underlying deformation mechanisms have relied on simulations. Here, we use interferometric four-dimensional scanning transmission electron microscopy to quantitatively map the mechanical deformations through which reconstruction occurs in small-angle twisted bilayer MoS 2 and WSe 2 /MoS 2 heterobilayers. We provide direct evidence that local rotations govern relaxation for twisted homobilayers, while local dilations are prominent in heterobilayers possessing a sufficiently large lattice mismatch. Encapsulation of the moiré layers in hBN further localizes and enhances these in-plane reconstruction pathways by suppressing out-of-plane corrugation. We also find that extrinsic uniaxial heterostrain, which introduces a lattice constant difference in twisted homobilayers, leads to accumulation and redistribution of reconstruction strain, demonstrating another route to modify the moiré potential. Lattice reconstruction crucially influences the electronic properties of twisted van der Waals structures. Here, the authors report a quantitative characterization of the mechanical deformations occurring in small-angle twisted bilayers and heterobilayers of 2D semiconductors via interferometric 4D scanning transmission electron microscopy.