The growth scale and kinetics of WS(2) monolayers under varying H(2) concentration

The optical and electronic properties of tungsten disulfide monolayers (WS(2)) have been extensively studied in the last few years, yet growth techniques for WS(2) remain behind other transition metal dichalcogenides (TMDCs) such as MoS(2). Here we demonstrate chemical vapor deposition (CVD) growth of continuous monolayer WS(2) films on mm(2) scales and elucidate effects related to hydrogen (H(2)) gas concentration during growth. WS(2) crystals were grown by reduction and sulfurization of WO(3) using H(2) gas and sulfur evaporated from solid sulfur powder. Several different growth formations (in-plane shapes) were observed depending on the concentration of H(2). Characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed etching of the SiO(2) substrate at low concentrations of H(2) and in the presence of an Ar carrier gas. We attribute this to insufficient reduction of WO(3) during growth. High H(2) concentrations resulted in etching of the grown WS(2) crystals after growth. The two dimensional X-ray diffraction (2D XRD) pattern demonstrates that the monolayer WS(2) was grown with the (004) plane normal to the substrate, showing that the WS(2) conforms to the growth substrate.