Roles of Salts in Chemical Vapor Deposition of Two-Dimensional Transition Metal Chalcogenides
Chemical vapor deposition (CVD) route has emerged as an effective method for the successful syntheses of two-dimensional (2D) materials with satisfactory crystal quality, especially for the syntheses of wafer-scale, thickness uniform or large domain size single-crystal transition metal Chalcogenides (TMCs). To achieve this, the salt-assisted CVD strategy has been proved to be powerful to reduce the high melting point of the metal related precursor, decrease the nucleation density and increase the reaction rate on the solid template. However, the specific roles of alkali metals and halides components still remain unclear. Herein, the functions of salts in the growth of TMCs have been discussed by summarizing some recent achievements in salt-assisted synthetic results, wherein salts are mainly introduced as additives in metal precursors to achieve the wafer-scale uniform growth of monolayer and thickness-tunable multi-layer TMCs, as well as serving as 3D templates (especially for NaCl) to realize the scalable production of TMCs. Moreover, the existing challenges and viable future directions are also proposed for in-depth understanding of the salt-assisted CVD methods, as well as for exploring more efficient CVD strategies.