Van der Waals heterostructures form a unique class of layered artificial solids in which physical properties can be manipulated through controlled composition, order and relative rotation of adjacent atomic planes. Here we use atomic-resolution transmission electron microscopy to reveal the lattice reconstruction in twisted bilayers of the transition metal dichalcogenides, MoS2 and WS2. For twisted 3R bilayers, a tessellated pattern of mirror-reflected triangular 3R domains emerges, separated by a network of partial dislocations for twist angles θ < 2°. The electronic properties of these 3R domains, featuring layer-polarized conduction-band states caused by lack of both inversion and mirror symmetry, appear to be qualitatively different from those of 2H transition metal dichalcogenides. For twisted 2H bilayers, stable 2H domains dominate, with nuclei of a second metastable phase. This appears as a kagome-like pattern at θ ≈ 2°, transitioning at θ → 0 to a hexagonal array of screw dislocations separating large-area 2H domains. Tunnelling measurements show that such reconstruction creates strong piezoelectric textures, opening a new avenue for engineering of 2D material properties.
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Additional data related to this paper is available from the corresponding authors upon reasonable request.
The computer code used for the image filtering is available from the corresponding authors upon reasonable request.
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We acknowledge support from the Engineering and Physical Sciences Research Council (EPSRC) grants EP/N010345/1, EP/P009050/1, EP/S019367/1, EP/S030719/1, EP/P01139X/1, EP/R513374/1 and the Centre for Doctoral Training (CDT) Graphene-NOWNANO, and the EPSRC Doctoral Prize Fellowship. We also acknowledge support from the European Graphene Flagship Project, European Quantum Technology Flagship Project 2D-SIPC (820378), European Research Council (ERC) Synergy Grant Hetero2D, ERC Starter grant EvoluTEM (715502), Royal Society and Lloyd Register Foundation Nanotechnology grant. V.E. (reconstruction simulations) acknowledges the support of the Russian Science Foundation (project no. 16-12-10411). P.H.B. acknowledges support from the Leverhulme Trust (Research Fellowship grant RF-2019-460). We thank Diamond Light Source for access and support in use of the electron Physical Science Imaging Centre (Instrument E02 and proposal numbers EM19315 and MG21597) that contributed to the results presented here.
The authors declare no competing interests.
Peer review information Nature Nanotechnology thanks Sergei Kalinin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Weston, A., Zou, Y., Enaldiev, V. et al. Atomic reconstruction in twisted bilayers of transition metal dichalcogenides. Nat. Nanotechnol. 15, 592–597 (2020). https://doi.org/10.1038/s41565-020-0682-9