Synthesis of component-controllable monolayer Mo x W (1- x ) S 2 y Se 2(1- y ) alloys with continuously tunable band gap and carrier type.

Alloying can effectively modify electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs). However, efficient and simple methods to synthesize atomically thin TMD alloys need to be further developed. In this study, we synthesized 25 monolayer Mo x W (1- x ) S 2 y Se 2(1- y ) alloys by using a new liquid phase edge epitaxy (LPEE) growth method with high controllability. This straightforward approach can be used to obtain monolayer materials and operates on a self-limiting growth mechanism. The process allows the liquid solution to come into contact with the two-dimensional grains only at their edges, resulting in epitaxy confined only along the in-plane direction, which produces exclusively monolayer epitaxy. By controlling the weight ratio of MoS 2 /WSe 2 (MoSe 2 /WS 2 ), 25 monolayer Mo x W (1- x ) S 2 y Se 2(1- y ) alloys with different atomic ratios can be obtained on sapphire substrates, with band gap ranging from WS 2 (1.55 eV) to MoSe 2 (1.99 eV) and a continuously broad spectrum ranging from 623 nm to 800 nm. By adjusting the alloy composition, the carrier type and carrier mobility of alloy-based field-effect transistors can be modulated. In particular, the adjustable conductivity of Mo x W (1- x ) S 2 y Se 2(1- y ) alloys from n-type to bipolar type is achieved for the first time. This general synthetic strategy provides a foundation for the development of monolayer TMD alloys with multiple components and various 2D materials.