Luminescent monolayer MoS2 quantum dots produced by multi-exfoliation based on lithium intercalation

Abstract An effective multi-exfoliation method based on lithium (Li) intercalation has been demonstrated for preparing monolayer molybdenum disulfide (MoS 2 ) quantum dots (QDs). The cutting mechanism of MoS 2 QDs may involve the complete breakup around the defects and edges during the reaction of Li x MoS 2 with water and its following ultrasonication process. The multiply exfoliation make the MoS 2 fragile and easier to break up. After the third exfoliation, a large number of monolayer MoS 2 QDs is formed. The as-prepared MoS 2 QDs show photoluminescence (PL) inactive due to the existence of 1T phase. After heating treatment, the PL intensity excited at 300 nm is enhanced by five times. The MoS 2 QDs solution has an excitation-dependent luminescence emission which shifts to longer wavelengths when the excitation wavelength changes from 280 nm to 370 nm. The optical properties are explored based on the quantum confinement and edge effect.