Large-scale MoS2(1-x)Se2x monolayers synthesized by confined-space CVD.

Alloy engineering is efficient in modulating the electronic structure and physical and chemical properties of Transition metal dichalcogenides (TMDs). Here, we develop an efficient and simple confined-space CVD strategy by using a smaller quartz boat nested in a larger quartz boat for the preparation of ternary alloy MoS2(1-x)Se2x monolayers on SiO2/Si substrates with controllable composition. The effect of hydrogen ratio of the mixed carrier gas (Ar/H2) on the resultant flakes are systematically investigated. A hydrogon ratio of 15% is demonstrated to be the most appropriate to synthesize large size (more than 400 μm) single crystalline MoS2(1-x)Se2x alloy monolayers. The composition of the alloy can also be changed in a full range (2x=0-2) by changing the weight ratio of Se and S powder. The as-grown monolayer MoS2(1-x)Se2x alloys present continuously high crystal quality in terms of Raman and PL measurements. Furthermore, to visible light (532 nm), the MoS2(1-x)Se2x based photodetectors display wonderful photoresponse with a fast response of less than 50 ms. Our work may be usedful in directing the synthesis of TMDs alloys as well as thier optoelectronic applications.