Cl ^– -Induced Step Engineering for Unidirectional Monolayer MoS ₂ Growth by Liquid-Precursor CVD

Achieving controllable orientation growth of MoS 2 on sapphire substrates is critically important. However, existing approaches typically rely on prolonged high-temperature substrate preannealing, which involves complex processes and high costs. In this work, we propose a facile strategy based on liquid-precursor chemical vapor deposition, achieving substrate engineering and oriented growth in one step by introducing the KCl additive. Our results show that Cl – can induce the formation of nanoscale steps on the sapphire surface during growth. These steps act as preferential nucleation sites, effectively guiding MoS 2 domains to adopt a dominant orientation. Field-effect transistors fabricated from the resulting MoS 2 exhibit stable n-type behavior and high current on/off ratios. This work presents a low-cost orientation-control strategy based on Cl – -induced step engineering, providing a practical pathway toward growth of high-quality two-dimensional transition metal dichalcogenides.