Preparation of Monolayer MoS₂ Quantum Dots using Temporally Shaped Femtosecond Laser Ablation of Bulk MoS₂ Targets in Water

Zero-dimensional MoS₂ quantum dots (QDs) possess distinct physical and chemical properties, which have garnered them considerable attention and facilitates their use in a broad range of applications. In this study, we prepared monolayer MoS₂ QDs using temporally shaped femtosecond laser ablation of bulk MoS₂ targets in water. The morphology, crystal structures, chemical, and optical properties of the MoS₂ QDs were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV-vis absorption spectra, and photoluminescence spectra. The analysis results show that highly pure, uniform, and monolayer MoS₂ QDs can be successfully prepared. Moreover, by temporally shaping a conventional single pulse into a two-subpulse train, the production rate of MoS₂ nanomaterials (including nanosheets, nanoparticles, and QDs) and the ratio of small size MoS₂ QDs can be substantially improved. The underlying mechanism is a combination of multilevel photoexfoliation of monolayer MoS₂ and water photoionization-enhanced light absorption. The as-prepared MoS₂ QDs exhibit excellent electrocatalytic activity for hydrogen evolution reactions because of the abundant active edge sites, high specific surface area, and excellent electrical conductivity. Thus, this study provides a simple and green alternative strategy for the preparation of monolayer QDs of transition metal dichalcogenides or other layered materials.