Unveiling Three-Dimensional Stacking Sequences of 1T Phase MoS₂ Monolayers by Electron Diffraction

The phase transition between semiconducting 1H to metallic 1T phases in monolayered transition metal dichalcogenides (TMDs) essentially involves three-dimensional (3D) structure changes of asymmetric relocations of S atoms at the top and bottom of the one-unit-cell crystals. Even though the phase transition has a profound influence on properties and applications of 2D TMDs, a viable approach to experimentally characterize the stacking sequences of the vertically asymmetrical 1T phase is still not available. Here, we report an electron diffraction method based on dynamic electron scattering to characterize the stacking sequences of 1T MoS₂ monolayers. This study provides an approach to unveil the 3D structure of 2D crystals and to explore the underlying mechanisms of semiconductor-to-metal transition of monolayer TMDs.