Modulating the Growth of Epitaxial MoS₂ on Au(111) Surfaces via an Ultra-High-Vacuum-Interconnected Apparatus

The intriguing two-dimensional (2D) molybdenum disulfide (MoS2) has unique potential in next-generation nanoelectronics and optoelectronics, engendering intense interest in its synthesis, especially using chemical vapor deposition (CVD). However, achieving high-quality 2D MoS2 remains a challenge, primarily limited by substrate quality in most instances. Herein, we develop an elegant way to create atomic-level well-defined Au(111) single-crystal films by ultra-high-vacuum (UHV)-interconnected techniques, including sputtering, annealing, and imaging, avoiding the environmental-impurity damage during crystallization and surface reconstruction compared to normal atmosphere-based operation. Benefiting from substrate engineering, this work succeeded in the epitaxial growth of uniform MoS2 monolayers using the CVD approach and further investigated the growth dynamics affected by key factors. It was revealed that the "substrate-to-precursor" distance determines the fluid-transfer-related growth region and modulates the morphology regularity, where the laminar-flow condition rather than the turbulence favors regular MoS2 monolayers. The S/Mo ratio contributes to the domain morphology and crystal orientation. Sulfur vapor transport and reaction product desorption are significantly influenced by the flow rate of the carrier gas. This work sheds dynamical insight into the nature of MoS2 monolayer synthesis and establishes a universal way to tackle challenges in preparing high-quality crystal substrates, enabling their generalization to other 2D materials.