Facile synthesis of MoS₂and Mo_xW_1-xS₂triangular monolayers

Single- and few-layered transition metal dichalcogenides, such as MoS₂and WS₂, are emerging two-dimensional materials exhibiting numerous and unusual physico-chemical properties that could be advantageous in the fabrication of unprecedented optoelectronic devices. Here we report a novel and alternative route to synthesize triangular monocrystals of MoS₂and Mo_xW_1-xS₂by annealing MoS₂and MoS₂/WO₃precursors, respectively, in the presence of sulfur vapor. In particular, the Mo_xW_1-xS₂triangular monolayers show gradual concentration profiles of W and Mo whereby Mo concentrates in the islands' center and W is more abundant on the outskirts of the triangular monocrystals. These observations were confirmed by atomic force microscopy, and high-resolution transmission electron microscopy, as well as Raman and photoluminescence spectroscopy. The presence of tunable PL signals depending on the Mo_xW_1-xS₂stoichiometries in 2D monocrystals opens up a wide range of applications in electronics and optoelectronics.