  Vapor transportation is the core process in growing transition-metal
dichalcogenides (TMDCs) by chemical vapor deposition (CVD). One inevitable
problem is the spatial inhomogeneity of the vapors. The non-stoichiometric
supply of transition-metal precursors and chalcogen leads to poor control in
products' location, morphology, crystallinity, uniformity and batch to batch
reproducibility. While vapor-liquid-solid (VLS) growth involves molten
precursors at the growth temperatures higher than their melting points. The
liquid sodium molybdate can precipitate solid MoS2 monolayers when saturated
with sulfur vapor. Taking advantage of the VLS growth, we achieved three kinds
of important achievements: (a) 4-inch-wafer-scale uniform growth of MoS2 flakes
on SiO2/Si substrates, (b) 2-inch-wafer-scale growth of continuous MoS2 film
with a grain size exceeding 100 um on sapphire substrates, and (c) pattern
(site-controlled) growth of MoS2 flakes and film. We clarified that the VLS
growth thus pave the new way for the high-efficient, scalable synthesis of
two-dimensional TMDC monolayers.
