Atomic resolution transmission electron microscopy and multiscale modelling have been used to illustrate that the lattice of MoS2 and WS2 homo-bilayers with small relative twist (< 3) reconstructs to form energetically favourable stacking domains separated by stacking faults. With a crystal alignment close to 3R stacking (θ ~ 0) mirror reflected triangular domains emerge separated by a network of partial dislocations which persist to the smallest twist angles. Scanning tunnelling measurements show contrast in electronic properties of 3R and 2H domains; for 3R domains we observe contrast in the tunnelling current due to layer-polarized conduction band states as a consequence of lack of both inversion and mirror symmetry. For small twist angles close to 2H stacking (θ ~ 60), stable 2H domains dominate where the nuclei of a previously unnoticed metastable stacking is limited to ~ 5nm in size. With relative twist θ~1, this appears as a kagome-like pattern which transitions to an hexagonal array of screw dislocations that separate large-area commensurate 2H domains.

Astrid Weston

University of Manchester