Large-scale MoS_2(1−x)Se_2x 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 MoS_2(1−x)Se_2x 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 MoS_2(1−x)Se_2x 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 MoS_2(1−x)Se_2x alloys present continuously high crystal quality in terms of Raman and PL measurements. Furthermore, to visible light (532 nm), the MoS_2(1−x)Se_2x 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 their optoelectronic applications. (paper)