Characterization and study of reduction and sulfurization processing in phase transition from molybdenum oxide (MoO₂) to molybdenum disulfide (MoS₂) chalcogenide semiconductor nanoparticles prepared by one-stage chemical reduction method

In this research, molybdenum disulfide (MoS₂) nanoparticles were prepared by chemical reduction method using MoO₃ and thiourea as a precursor. The physical properties of the synthesized MoO₂-MoS₂ nanoparticles annealed at different temperatures of 200, 300, 750 C have been investigated, before and after exposure to sulfur vapor. The nanostructure of nanoparticles has been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) analyses and UV-Vis spectrophotometer. The X-ray diffraction analysis showed the formation of MoS₂ single phase at annealing temperature of 750 C in the presence of sulfur vapor. The Raman spectrum of the nanoparticles revealed that the formation of MoS₂ at 750 C after annealing in sulfur vapor. The values of band gap were obtained in the range of 3.64-3.17 eV and 3.47-1.95 eV for MoS₂ nanoparticles before and after exposure to sulfur vapor, respectively. According to SEM images, the grain size decreases with increasing annealing temperature up to 750 C. Also, nanoplate-nanoparticles of MoS₂ are formed at annealing temperature of 200-750 C. The TEM images of MoS₂ nanoparticles at T_a = 750 C confirm that the nanoparticles have a homogeneous distribution with a hexagonal structure. The FTIR spectra of the MoS₂ nanoparticles showed the peaks at about 467 cm ^-1 belong to the characteristic bands of Mo-S. (orig.)