Sodium chloride-assisted CVD enables controlled synthesis of large single-layered MoS₂

Thin-layer MoS₂ has attracted much interest because of its potential in diverse technologies, including electronics, optoelectronics and catalysis these few years. In particular, finding a simple and effective solution for large-scale growth of thin-layer semiconductor nanosheets is a prerequisite for achieving their excellent performance. In this paper, we investigated four different substrates under identical conditions for MoS₂ film growth and observed a strong correlation between substrate surface conditions and MoS₂ growth. To enhance substrate performance, a low-concentration NaCl water solution (25 mg mL^-1) was employed for pre-treating the substrate surface, thereby modifying its initial state. In the chemical vapor deposition (CVD) growth environment, the introduced halide ions served as surface dangling bonds. The pre-treated led to a remarkable 90% increase in the growth rate of MoS₂ on the substrate surface, facilitating the production of large monolayer MoS₂ sheets (∼200 μm). This growth mechanism further enabled the manufacturing of ultra-large single crystals (∼1 mm). Consequently, our research presents a straightforward and cost-effective approach for the large-scale production of nanosheets. Field-effect transistors (FETs) based on the pre-treated monolayer MoS₂ exhibited high mobility (12 cm² V^-1 s^-1) and a large on/off ratio (10⁴). Therefore, our research provides a simple and low-cost approach for large-scale production of nanosheets for use in high-quality electronics over large areas.