Photoluminescence and UV photosensitivity of few-layered MoS2 nanosheets synthesized under different hydrothermal growth times

MoS2 flower-like microspheres composed of 2D nanosheets were prepared using the simple and cost-effective method of hydrothermal. The effects of hydrothermal process time variations on the structural, morphological, elemental composition, electrical, and optical properties of MoS2 nanopowders were investigated. X-ray diffraction patterns of all samples exhibited two main peaks at 33.4°–58.8° which were attributed to the (100) and (110) peaks of 2H-MoS2. The appearance of two first-order Raman active modes of MoS2, namely E12g and A1g at 378, and 402 cm−1, respectively, confirmed the formation of MoS2. SEM images showed that every MoS2 flower-like microspheres have composed of very thin nanosheets with a mean diameter of about 35 nm. HRTEM images clearly show that the MoS2 nanosheets have been formed by 10–20 layers that partially stand perpendicularly on the surface of the MoS2 microspheres. The bandgap energy of samples has increased from 1.26 to 1.62 eV by increasing the hydrothermal growth time from 2 to 24 h, respectively. The increase in the bandgap of samples was attributed to the reduced number of layers. Samples prepared at higher growth times of 8, 12, and 24 h show a broad photoluminescence peak, assigned as the I-exciton. This peak shifts to lower energies and becomes less prominent with the increasing number of layers. Temperature-dependent Hall effect measurements were performed and n-type conductivity was confirmed and electrical parameters were extracted. Samples were exposed to 230 nm UV light, and their photosensitivity was recorded. The sample prepared at the highest growth time of 24 h showed the highest UV response, with the photocurrent of about 165 µA under 3 V bias voltage.