Molybdenum disulfide (MoS₂) has attracted attention due to its unique electronic and optical properties from bulk indirect bandgap (~1.2 eV) to direct bandgap (~1.8 eV) in monolayer. The MoS₂ thin films were fabricated using the three-zone chemical vapor deposition (CVD) in a quasi-closed crucible. Effect of thermal annealing on MoS₂ thin films and formation of MoS₂ quantum dots (QDs) were investigated by Raman-scattering and photoluminescence (PL) spectroscopy, as well as atomic force microscopy (AFM) and polarization dependent PL.

Topography characterization showed that MoS₂ QDs and holes were formed from post thermal annealing for 0.5 hours at 350°C in the air, due to the formation of sulfur deficiencies at the MoS₂ film. The diameter of the QDs range from 10 to 30 nm, and as the annealing time was extended, the size and the number of QDs increased. A slight increase in MoS₂ thin film thickness can be observed based from the Raman shift difference between A1g and E_2g^1 peaks. Subsequent 30-minute thermal annealing at 350°C in the air led to both further QD growth and layer thinning. The MoS2 thin films were completely evaporated after 4 hours of annealing. PL spectra showed that the A exciton emission line red-shifted slightly and the intensity increased with annealing duration while the peak width remained mostly unchanged. The redshift is due to formation of S deficiency; increase in intensity is attributed to QD formation. Moreover, polarization-resolved PL spectra showed no trend as annealing time was increased

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