Na-Assisted Molecular Beam Epitaxy of MoS₂

Transition metal dichalcogenides (TMDs) hold great promise for next-generation electronics, where both large-domain growth and atomic-level doping control are essential for optimal device performance. While molecular beam epitaxy (MBE) provides unparalleled precision in thickness and composition control, its application to TMD growth has been fundamentally limited by small domain sizes. Here, we demonstrate a sodium-assisted MBE (Na-MBE) technique to achieve single-crystalline MoS₂ domains exceeding 1 μm on Au(111), which is an order of magnitude larger over MoS₂ grown on the same substrate with standard MBE techniques. Crucially, in situ studies reveal Na₂S as a key growth intermediate that enhances growth rate and sulfur supply. The versatility of this method is demonstrated through the synthesis of compositionally uniform alloyed TMDs (Mo_0.5W_0.5S₂), highlighting its potential for producing doping-controlled 2D materials with micron-scale single-crystalline domains.