Hydrothermal Synthesis of Hierarchically Organized MoS2 and Formation of Films Based on It

Abstract

The effect of hydrothermal synthesis parameters on the crystal structure and morphology of MoS₂ particles has been shown. The results of synchronous thermal analysis showed that at the concentration of molybdenum cations of 0.05 mol/L, the increase in the duration of hydrothermal treatment leads to a decrease in the total mass loss (Δm), and the increase in c(Mo), on the contrary, results in a significant increase in the total Δm value. The dependence of the exo-effect maximum position, related to the MoS₂ oxidation with the formation of MoO₃, on the synthesis conditions has been determined. According to X-ray powder diffraction data, the 1T-MoS₂ phase is formed at minimum c(Mo) and duration of heat treatment. Increasing the time duration leads to the transformation of 1T-phase into 2H-MoS₂. With increasing c(Mo), the 2H-phase transforms to 1T-MoS₂ and further to 1T/2H-MoS₂. The transformation of MoS₂ structure has been also analyzed by Raman spectroscopy. According to the results of scanning electron microscopy (SEM), all samples represent flower-like nanostructures consisting of twisted nanosheets. According to transmission electron microscopy data, individual nanosheets with a length of 50–500 nm are formed after delamination of molybdenum disulfide structures. The microstructure of the obtained MoS₂ film has been studied by SEM and atomic force microscopy. Analysis of the film surface by Kelvin-probe force microscopy allows one to establish that the material has high electrical conductivity, and the work function value of the film surface has been calculated.