Exclusive Generation of Single-Atom Sulfur for Ultrahigh Quality Monolayer MoS₂ Growth

Preparation of high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs) is the precondition for realizing their applications. However, the synthesized 2D TMDCs (e.g., MoS₂) crystals suffer from low quality due to the massive defects formed during the growth. Here, we report single-atom sulfur (S₁) as a highly reactive sulfur species to grow ultrahigh-quality monolayer MoS₂. Derived from battery waste, sulfurized polyacrylonitrile (SPAN) is found to be exclusive and efficient in releasing S₁. The monolayer MoS₂ prepared by SPAN exhibits an ultralow defect density of ∼7 × 10¹² cm^-2 and the narrowest photoluminescence (PL) emission peak with full-width at half-maximum of ∼47.11 meV at room temperature. Moreover, the statistical resonance Raman and low-temperature PL results further verify the significantly lower defect density and higher optical quality of SPAN-grown MoS₂ than those of the conventional S-powder-grown samples. This work provides an effective approach for preparing ultrahigh-quality 2D single crystals, facilitating their industrial applications.