Fabrication of High Proportion of WS₂ Monolayers Using Liquid Phase Exfoliation Method

Due to their unique properties, tungsten disulfide (WS₂) nanosheets, preferably monolayers, are promising materials for sensing, optoelectronic, catalysis, and energy storage applications. A simple, reliable, and cost-effective synthesis method is desirable to realize their applications. The liquid phase exfoliation method, which involves the mechanical exfoliation of layered materials in a solvent, has proven to be a promising technique for synthesizing nanosheets with high yields. In this study, we systematically examine the optimization of the fabrication of WS₂ nanosheets by exfoliating the WS₂ powder in isopropyl alcohol, a low boiling point solvent, using a low-power probe sonicator. The investigation of the atomic force microscopy images reveals that the exfoliated nanosheets comprise a significant proportion of monolayers and bilayers. Our study finds that the proportion of monolayers and bilayers can be elevated by more than 20% if the dispersions are centrifuged at higher speeds. Moreover, we show that prolonged sonication increases the proportion of monolayers, such as 11% more monolayers can be fabricated with a five-fold increase in sonication time.