Enhanced epitaxial growth of two-dimensional monolayer WS2 film with large single domains

The emerging of graphene has stimulated the exploration of two-dimensional (2D) nanomaterials. As a kind of important semiconducting 2D materials, WS2 shows great potentials in electronics, optoelectronics, and photonics, etc.; however, the synthesis of high quality, large area, uniform and epitaxial 2D WS2 monolayer films is still a challenge. Herein, we report the epitaxial growth of WS2 on sapphire with excellent electrical and optoelectronic properties via an enhanced chemical vapor deposition method. With the assistance of Na2WO4 as well as the investigation of related growth mechanism, large single crystal triangular WS2 monolayer flakes with well-defined orientations are achieved. The corresponding single crystal domain size is larger than 1 mm together with the centimeter-scale continuous film realized. Once fabricated into transistors, the monolayers exhibit excellent device properties, such as high mobility and large on/off current ratio. Also, these devices give respectable photoresponse properties when operated in the photoconductive mode. The peak responsivity can reach 4.6 A W−1. All these results demonstrate the high quality of as-synthesized WS2 monolayers, indicating the bright future of this synthesis technology for 2D materials towards practical applications.