Figure 1

Morphology of QDs. (a) Transmission electron microscopic images of MoS₂ QDs. The inset shows the statistical size distribution of QDs from the transmission electron microscopy (TEM). (b) STM images of MoS₂ QDs on a HOPG surface. The image has been taken in constant current mode at a bias voltage of − 0.5 V and 0.5 nA current. (c) The UV–Visible absorption spectrum of the MoS₂ QDs; the inset shows the Tauc plot assuming a direct bandgap material. (d) Raman spectra MoS₂ bulk and QDs, showing the in-plane (\(E_{2g}^{1}\)) and out-of-plane (\(A_{1g}^{{}}\)) vibrational modes of the S atoms. The blue shift of the peak for QDs is due to quantum size effects in MoS₂. (e) Photoluminescence (PL) spectra of the aqueous solution of MoS₂ quantum dots for different excitation wavelengths; (f) the dependence of emission wavelengths on excitation wavelengths. The inset shows the quantum dot suspension in water under white light and its blue fluorescence under UV irradiation.