Layer-modulated synthesis of uniform tungsten disulfide nanosheet using gas-phase precursors

The synthesis of layered transition-metal-disulfide (MS₂, M = Mo, W) nanosheets with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this report, we describe a synthesis process of WS₂ nanosheets with layer controllability and high uniformity using chemical vapor deposition (CVD) and WCl₆ and H₂S as gas-phase precursors. Through this process, we can systematically modulate the thickness of WS₂ nanosheets by controlling the duration of the reaction between WCl₆ and H₂S. The CVD-grown WS₂ nanosheets exhibit good stoichiometry as well as dependencies of a clear Raman shift and bandgap on the number of layers. These properties are confirmed by X-ray photoemission spectroscopy, Raman spectroscopy, and photoluminescence measurements. The number of layers of WS₂ nanosheets is confirmed by atomic force microscopy. Finally, we demonstrate the fabrication and performance of a photodetector based on a hybrid structure consisting of graphene and a WS₂ nanosheet.