Salt-promoted growth of monolayer tungsten disulfide on hexagonal boron nitride using all chemical vapor deposition approach

Monolayer tungsten disulfide (WS2), an emerging two-dimensional (2D) direct-bandgap semiconductor, provides new prospects for next-generation electronic, optoelectronic and valleytronic devices. However, the physical properties of 2D WS2, are seriously perturbed by various extrinsic disorders to a large extent. Despite encap-sulating exfoliated WS2 with hexagonal boron nitride (h-BN) flakes can effectively screen the surrounding dis-orders, its scalability is not applicable to large-area electronics. In this work, the construction of monolayer WS2 on h-BN is achieved with an all chemical vapor deposition (CVD) approach by using alkali metal salt to promote the growth of WS2. Detailed characterizations indicate that WS2 deposited on h-BN exhibits improved optical and electrical properties, as compared to those on SiO2/Si substrates. Furthermore, the influence of depositing WS2 on h-BN and salt-promoted growth behavior of WS2 is systematically investigated, highlighting the important role of salt in constructing the heterobilayers. This work paves a practical way for synthesis of 2D materials on h-BN to further probe their intrinsic properties and enable a plethora of potential applications.