Enhancing stability by tuning element ratio in 2D transition metal chalcogenides

Two-dimensional (2D) transition metal chalcogenides (TMCs) are known to be susceptible to the atmosphere, which greatly obscures the intrinsic physical and chemical properties. The quantitative origin of the instability on the atomic scale has not been well investigated due to the lack of environmentally stable TMCs sample. Here, we find the stability of the grown TMCs is strongly relevant to their initial element ratios, and thus the stoichiometric bonded TMCs have favorable stability, benefitted from the TMCs with controllable chalcogenisation. In this study, the degree of structural degradation has been quantitatively defined by the reduced element ratio of chalcogen to metal through the time-dependent characterizations, and the non-stoichiometric ratios in TMCs reveal the atomic lattices with point defects like additive bonds or vacancies inside. This study not only provides a potential view to fabricate environmentally stable TMCs based devices, but also will bring an effective feasibility of stacking stable vertical heterostructures.