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ABSTRACT Scalable synthesis of two-dimensional molybdenum disulfide (MoS 2 ) via chemical vapor deposition (CVD) is of considerable interests for many applications in electronics and optoelectronics. Here, we investigate the CVD growth of MoS 2 single crystals on sapphire substrates by using thermally evaporated molybdenum trioxide (MoO 3 ) thin films as molybdenum (Mo) source instead of conventionally used MoO 3 powder for co-evaporation synthesis. The MoO 3 thin film source provides uniform Mo vapor pressure in the growth chamber resulting in clean and reproducible MoS 2 triangles without any oxide or oxysulfide species. Scanning electron microscopy, Raman spectroscopy, photoluminescence spectroscopy and atomic force microscopy characterization were performed to characterize the growth results. Very high photoluminescence (PL) response was observed at 1.85 eV which is a good implication of high optical quality of these crystals directly grown on sapphire substrate. 

ABSTRACT Chemical vapor deposition (CVD) growth of two-dimensional molybdenum disulfide (MoS 2 ) using molybdenum trioxide (MoO 3 ) and sulfur (S) powder often results in intermediate molybdenum oxy-sulfide (MoOS 2 ) species along with MoS 2 due to a lack of control over the vapor pressure required for the clean growth. Much effort has been devoted in understanding and controlling of these intermediate MoOS 2 specifies. Here, we show that with a second step sulfurization at moderate temperatures, these MoOS 2 crystals can be transformed to monolayer MoS 2 crystals. Scanning electron microscopy, Raman and photoluminescence spectroscopy and atomic force microscopy characterization carried out before and after re-sulfurization confirm the monolayer MoS 2 growth via this route. This study shows that MoOS 2 formed at the intermediate state can be successfully recycled to MoS 2 .