Suppressing Nucleation in Metal-Organic Chemical Vapor Deposition of MoS Monolayers by Alkali Metal Halides.

Toward the large-area deposition of MoS layers, we employ metal-organic precursors of Mo and S for a facile and reproducible van der Waals epitaxy on c-plane sapphire. Exposing c-sapphire substrates to alkali metal halide salts such as KI or NaCl together with the Mo precursor prior to the start of the growth process results in increasing the lateral dimensions of single crystalline domains by more than 2 orders of magnitude. The MoS grown this way exhibits high crystallinity and optoelectronic quality comparable to single-crystal MoS produced by conventional chemical vapor deposition methods. The presence of alkali metal halides suppresses the nucleation and enhances enlargement of domains while resulting in chemically pure MoS after transfer. Field-effect measurements in polymer electrolyte-gated devices result in promising electron mobility values close to 100 cm V s at cryogenic temperatures.