Optical, structural and dielectric properties of solvothermally grown molybdenum sulfide nanosheets

Abstract

MoS2 nanosheets have been synthesized by simple and conventional solvothermal methods. FEG-TEM images reveal that the produced MoS2 sample has a hexagonal crystal structure with large (2μm) nanosheets. The XRD and Raman spectra of the samples also confirm the hexagonal crystal phase. The schematic refined unit cell with electron density mapping is visualized after Rietveld refinement. The optical properties such as absorbance, PL, refractive index, extinction coefficient, dielectric constant, optical conductivity, etc. have been investigated in the wavelength range of 330nm to 1000nm. The normal dispersion (ND) and the anomalous dispersion (AD) regions have been observed in the refractive index spectrum. The estimated carrier concentration has been found to be 5×104cm−3. The temperature-dependent indirect bandgap of MoS2 has been simulated using a semi-empirical formula based on electron-phonon coupling and it decreases with increasing temperature. The calculated average lifetime of carriers is 1.17 ns. The grown MoS2 shows large dielectric constant and low tangent loss in the frequency range of 5–500 kHz. The Nyquist plot of the sample gives the NTCR (negative temperature coefficient of resistance) behaviour like a semiconductor. The activation energy (EA) has been estimated from temperature dependence AC conductivity.