Controlled synthesis of WS2 with different layers by tuning flow rates

Two-dimensional tungsten disulfide (WS2) has been widely studied owing to its superior optical and electrical properties. Since the growth mechanism is unclear, controllable synthesis of 2D WS2 is still a challenge. Based on the analysis of the relationship between the mass transfer rate and the chemical reaction rate of the reactants, we control the lateral and longitudinal growth of the films by regulating the Ar flow rate in the growth stage, and then realize the controllable synthesis of WS2 films with monolayer, bilayer and tri-layer. In addition, back-gated FETs were fabricated based on WS2 thin films with different layers. Monolayer WS2 showed n-type character-istics with a carrier mobility of similar to 1.5 cm(2) V-1 s(-1), whereas bilayer WS2 showed a higher mobility of similar to 13 cm(2) V-1 s(-1) with the I-on/I-off ratio of similar to 10(6). Our work paves the way for the development of next generation photoelectronic devices based on 2D materials.