Abstract
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.
Highlights
Bulk transition metal dichalcogenide (TMD) crystals are composed of regularly stacked monolayers, each consisting of a triangular sublayer of metal atoms at the mirror-symmetry plane between two identical triangular chalcogen sublayers
The electronic properties of these 3R domains appear qualitatively different from 2H TMDs, featuring layer-polarized conduction band states caused by lack of both inversion and mirror symmetry
While lattice reconstruction in twisted bilayers close to 3R-type is morphologically similar to graphene, twisted homo- and hetero-bilayers of TMDs offer a broader diversity of physical properties prescribed by the lack of inversion symmetry in the constituent layers
Summary
As compared to twisted graphene structures, twisted homo- and hetero-bilayers of TMDs offer a broad diversity of nanoelectronic properties prescribed by the lack of inversion symmetry in the constituent layers. We find that lattice reconstruction for P-oriented bilayers creates condition for the formation of sizeable domains of 3R stacking (which is rarely found in bulk MoS2 and WS2 crystals) and features intrinsic asymmetry of electronic wavefunctions which can be used for electrical tuning of the optical properties of such twisted bilayers by a displacement field. AP structures host strong piezoelectric textures with potential for creating twist-controlled networks of quantum dots and nanowires with non-trivial electronic and optoelectronic properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
