Reaction-Kinetics-Driven Epitaxy of Wafer-Scale WS₂ by Molten Precursor Engineering

Two-dimensional transition-metal dichalcogenides (TMDCs) are promising atomically thin semiconductors for next-generation electronics and optoelectronics. However, wafer-scale epitaxy of tungsten-based TMDCs is limited by the chemical inactivity of conventional oxide precursors, which restricts the formation and incorporation of growth species. Here we introduce a solid-liquid-equilibrium molten precursor formed from mixed WO₃/Na₂WO₄ that is proposed to generate reactive WO₄ growth units and stabilize the tungsten supply. The resulting WS₂ grows through sustained lateral propagation, producing crystallographically aligned monolayer wafers with narrow excitonic linewidths ascribed to suppressed disorder. First-principles calculations show that the molten precursor shifts the rate-limiting step from oxide conversion to edge incorporation, while sodium-mediated attachment lowers the propagation barrier. This work establishes precursor-state engineering as a general route to overcome reaction-limited regimes in tungsten-based two-dimensional TMDCs epitaxy.