Controllable synthesis of millimeter-size single crystal WS2

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) have attracted much attention due to their unique structure and novel physical properties. Although much progress has been achieved in recent years, it is still a great challenge to synthesize TMDs single crystals with large size controllable. In this paper, we report a controllable method to synthesize single crystalline triangular WS2 with millimeter-scale in length by modulating nucleation and lateral growth process. The monolayer WS2 triangles with edge lengths larger than 1.7 mm were successfully grown on sapphire substrates by using this method. First principle calculation reveals that higher charge density and binding energy on WS2/sapphire interfaces result in the lateral growth to enlarge the size of the triangles on sapphire. On SiO2/Si, however, the triangles appear vertical growth with a size of 200 μm in length. FET transistor based on the triangles on SiO2/Si was fabricated. The on/off ratio of the device could approach to 103, and the field-effect mobility is measured approximately 11 cm2/V·s. The method in this work possibly paves a new way to the growth of WS2 and other TMDs single crystals with large domain size.