Scalable Synthesis of WS₂ Monolayers Without Chemical Additives

Tungsten disulfide (WS₂) monolayers exhibit novel physical and electronic properties, making them promising candidates for catalysis and electronic applications. To realize these applications, developing a reliable and scalable method for synthesizing high-quality WS₂ monolayers is crucial. Achieving large-area WS₂ growth has been achieved in prior studies, particularly using sodium chloride as a growth promoter; however, this introduces impurities that can negatively impact their intrinsic properties. In this study, we focus on synthesizing larger WS₂ monolayers without employing any additional chemical additives. We utilize the chemical vapor deposition (CVD) method to grow monolayers of WS₂ on Al₂O₃ (0001) substrates, employing WO₃ and sulfur as precursors. To enhance the vapor pressure of WO3, we introduce an additional quartz tube within the furnace, which allows for high WO₃ vapor pressure without requiring elevated temperature. Another quartz tube is used to direct sulfur vapor toward the substrate, optimizing the availability of sulfur vapor during growth. This experimental setup successfully enables the growth of WS₂ monolayers reaching sizes of tens of micrometers, as confirmed by atomic force microscopy (AFM). These large WS₂ monolayers have the potential to be utilized in catalysis applications or be combined with other catalysts to create composite catalysts.