Wafer-Scale Uniform Synthesis of 2D Transition Metal Dichalcogenides Single Crystals via Chemical Vapor Deposition

CONSPECTUS:Two-dimensional(2D)semiconducting transition metal dichalcogenides(TMDCs),most with a formula of MX2(M=Mo,W;X=S,Se,etc.),have emerged as ultrathin channel materials in next-generation electronics,due to their atomic thickness,tunable bandgap,and relatively high carrier mobility,etc.To propel their practical applications in integrated circuits,large-scale preparation of large-domain MX2 single crystals and singlecrystal films is significantly important.Among all the synthetic methods,chemical vapor deposition(CVD)has shown great promise for the controllable syntheses of large-area uniform 2D materials with electronic-grade quality and reasonable cost.So far,intensive efforts have been devoted to the controllable growth of MX2 single crystals with large sizes,controlled thicknesses,fast growth rates,and unidirectional orientations.However,due to the complexity of the precursor species(mostly like solid powders)and their gradient feeding distributions along the gas flow direction,it is still a huge challenge to synthesize large-area MX2 samples with centimeter-scale uniformity,which inevitably hinders their practical applications in industry.More significantly,due to the noncentrosymmetric structures of MX2,antiparallel domains and twin grain boundaries usually evolved on most substrates(e.g.,mica,C-sapphire).These defective grain boundaries usually exhibit metallic characteristics and serve as conducting channels,seriously impairing the electrical and optical properties of related devices.