Large-area high quality MoS2 monolayers grown by sulfur vapor counter flow diffusion

Large-area uniform monolayer MoS2 films are prepared via an atmospheric pressure chemical vapor deposition method. Sulfur vapor counter flow diffusion lowers its concentration at the reaction zone and makes MoO3 sulfurization slow and gentle, which is beneficial for monolayer MoS2 growth. Suboxide MoO3-x domains, co-existing MoS2 mono-and multi-layers, monolayer MoS2 films, triangular MoS2 monolayer flakes are successively formed in the growth zone along the gas flow direction. Optical microscopy, atomic force microscopy, transmission electron microscopy, UV-vis, Raman and photoluminescence spectra demonstrate that the as-grown films are continuous monolayers over a large area, and are of high quality comparable to exfoliated monolayer MoS2. This method can also be applied to synthesize MoS2/MoO2 microplates without the assistance of metal oxides.