Transformation from dendritic to triangular growth of WS2 via NaCl assisted low-pressure chemical vapor deposition

Tungsten disulfide (WS2) is a promising two-dimensional material owing to its remarkable optical, electronic, and electrocatalytic behavior. However, morphology of this material varies significantly with growth conditions. In this work, we use salt-assisted low-pressure chemical vapor deposition (LP-CVD) to grow WS2 crystals of a few layers reaching over 50 μm in size on SiO2/Si substrates. We observe a transition from large, dendritic to triangular growth by systematically varying the amount of the NaCl promotor material as well as the presence of intermediate Wx+ states for low NaCl amounts. The transition from dendritic to triangular growth is discussed in the context of diffusion limited aggregation, with the transformation likely being the result of reduced formation energy, owing to increasing concentrations of transition metal oxyhalides for given precursor quantities. These results help to clarify the role of effects of the NaCl precursor in salt-assisted LP-CVD of WS2 and provide a new means to tune the morphology of this material.