The properties of two-dimensional sheets of layered transition metal dichalcogenides such as tungsten diselenide (WSe2) depend on how the layers stack. For example, the more common 2H phase has a two-layer AB repeat and is centrosymmetric, but the rare 3R phase has a three-layer ABC repeat and different electronic properties because it is noncentrosymmetric. Shearer et al. grew WSe2 nanoplates through chemical vapor deposition that had screw dislocations. A triangular dislocation grew noncentrosymmetric layers, a hexagonal dislocation grew centrosymmetric layers, and mixed dislocations grew weakly noncentrosymmetric layers. They explored the changes in properties with stacking, such as strong second-harmonic generation with the noncentrosymmetric material.
J. Am. Chem. Soc. 10.1021/jacs.6b12559 (2017).