Stepwise Sulfurization from MoO₃ to MoS₂ via Chemical Vapor Deposition

Abstract

Chemical vapor deposition\n(CVD) is used widely to synthesize monolayer\nand few-layer transition metal dichalcogenide molybdenum disulfide\n(MoS₂), a two-dimensional (2D) material with various applications\nin nanoelectronics, catalysis, and optoelectronics. However, the CVD\nsynthesis of 2D MoS₂ is highly sensitive to small changes\nin growth parameters and the growth mechanism has not been extensively\nstudied. This work systematically investigates the effect of sulfur\nconcentration on CVD synthesis of MoS₂ using molybdenum\ntrioxide (MoO₃) and sulfur precursors. We find that with\nincreasing concentration of sulfur vapor, intermediate products of\nmolybdenum dioxide (MoO₂) and molybdenum oxysulfide (MoOS₂) can form during a stepwise sulfurization of MoO₃ to the final product of MoS₂. The intermediate MoOS₂, formed due to sulfur vapor deficiency, can be fully converted\nto MoS₂ with further sulfurization. We show that the local\nsulfur to molybdenum vapor ratio at the growth substrate critically\ndetermines the growth products. This study thus highlights the importance\nof keeping the molar ratio of sulfur to molybdenum vapor well in excess\nof the stoichiometrically required ratio of 3.5:1 in order to grow\n2D MoS₂.