Effect of temperature on the salt-assisted growth of monolayer tungsten disulfide via low-pressure chemical vapor deposition

Monolayer tungsten disulfide (WS₂) is a promising material for various device applications due to its unique electronic and optical properties. However, achieving an efficient and cost-effective method for synthesizing a large area, uniform WS₂ is still a challenge. In this work, we demonstrate the synthesis of single layer WS2 crystallites by salt-assisted low-pressure chemical vapor deposition and present a systematic study of the effect of temperature on the morphology, structure, thickness and optical properties of the as grown WS₂ films. An optimized amount of NaCl was mixed with WO₃ powder to use as the promoter. We observe transitions between triangular, hexagonal, fractal and dendritic structures as the temperature range is varied, as well as varied amounts of oxygen defects as evidenced by XPS and photoluminescence measurements. By varying the growth temperature between 700 °C to 900 °C, we further observed an increase in the size of the individual flakes up to 50 µm as well as an increase in the extent of growth. As grown WS₂ samples were further characterized under Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. The results of this work pave a way to optimize growth condition for obtaining large area, high quality uniform WS₂.