Sonication-assisted ion-intercalation exfoliation of MoS₂ quantum dots

Synthesis of MoS₂ quantum dots (QDs) by a sonication-assisted ion-intercalation process where sodium hydroxide (NaOH) is used as sodium (Na⁺) and hydroxyl (OH⁻) ions source for the intercalation purpose is reported. The exfoliation method results in well-exfoliated mono- to few-layered QDs as illustrated by the atomic force microscopy (AFM) measurements, showing a thickness of < 1.6 nm, and confirmed by X-ray diffraction (XRD) studies where the characteristic peak at 2θ = 14.4° of bulk 2H-MoS₂ disappears. The Raman spectroscopy measurements of the QDs show a frequency difference of 19.8 cm⁻¹ between the E and A_1g vibration modes and are in good agreement with the AFM and XRD results. The reported exfoliation technique resulted in an improvement of ~ 7% in production yield with a total production yield of ~ 20%, higher than the previous reports. The QDs have average lateral size of 3.7 ± 1.0 nm as determined from the HRTEM images. Graphical abstract: [Figure not available: see fulltext.].