Controlled synthesis and mechanism of large-area WS2 flakes by low-pressure chemical vapor deposition

WS₂ flakes have been grown successfully on SiO₂(300 nm)/Si substrate via traditional low-pressure chemical vapor deposition method. We studied the controllable growth of WS₂ flakes on three of the growth parameters: the time of S-precursor introduction, the temperature of WO₃ precursor and the growth temperature. The as-prepared products were characterized by X-ray photoemission spectroscopy, Raman spectra and atomic force microscopy. It is found that the morphologies of WS₂ flakes and the products are highly dependent on the concentration of S-precursor, W-precursor and the ratio of W atoms to S atoms, while large-area WS₂ flakes up to 160 μm can be obtained. If the ratio of W/S is ≤1:2, we obtain triangular and hexagonal WS₂ flakes. On the contrary, if the ratio of W/S is >1:2, besides WS₂ flakes, W nanowires will be formed owing to the superfluous W atoms. This study can provide an important and practical guide to preparing large-area and high-quality two-dimensional transition metal dichalcogenides materials.