Droplet-Mediated Vapor–Liquid–Solid Growth of Pyramidal MoS2 via the Supersaturation-Governed Transition from Lateral Growth to Vertical Stacking

Abstract

Three-dimensional MoS2 structures provide enriched interlayer coupling, abundant edge/step sites, and thickness gradients, opening opportunities for tailoring electronic and interfacial functionalities. Controlled growth of pyramidal MoS2 remains challenging because its structure is governed by precursor supply, local supersaturation, and secondary nucleation. Herein, we report a droplet-mediated vapor–liquid–solid CVD strategy for the controllable growth of pyramidal MoS2 using precursor-rich Na–Mo–O droplets as localized precursor reservoirs and reaction interfaces. Statistical analysis reveals a correlation between droplet diameter and pyramid lateral size, indicating the strong coupling between droplet-mediated supply and crystal growth. Combined classical nucleation theory and DFT calculations support a supersaturation-governed growth transition. Under low effective interfacial supersaturation, upper-step nucleation is less accessible and lateral growth is favored, whereas increasing effective interfacial supersaturation progressively facilitates secondary nucleation and step stacking. KPFM further reveals a stepwise evolution of surface potential along the thickness gradient. Despite the microscale channel thickness and interlayer screening, back-gated transistors based on pyramidal MoS2 remain electrically addressable, exhibiting apparent two-terminal field-effect mobilities of 4–6 cm2 V–1 s–1 and on/off ratios on the order of 103. This work establishes a controllable route to thickness-graded three-dimensional MoS2 structures and provides mechanistic insight into stacking growth in layered semiconductors.