We introduce liquid ammonium sulfide as a reliable and carbon-free sulfur precursor for synthesizing large-area transition metal disulfides (TMdS) in chemical vapor deposition. The flux of sulfur during TMdS growth is precisely controlled by passing a known amount of carrier gas through a bubbling system containing liquid ammonium sulfide. However, controlling the flux of sulfur through the conventional evaporation of sulfur powder using a heating belt remains a challenge. By achieving controllability of sulfur flux, we study growth kinetics such as nucleation density and growth rate. Furthermore, the continuous supply of the sulfur precursor results in the growth of a large-area monolayer and a few layers of MoS2 film. In addition, we present the feasibility of ammonium sulfide as an effective and clean precursor for the growth of a wide range of TMdS, thus enabling it to serve as a universal sulfur precursor.
