The Study Of Controlled Growth Of Two-Dimensional Molybdenum Disulfide

Molybdenum disulfide(MoS2) is one kind of two-dimensional(2D) layered material consisting of one Mo layer sandwiched between two S layers. Properties of MoS2 highly depend on its morphology and thickness. Therefore controlled growth MoS2 is very important to its properties and applications. In this work, controlled growth MoS2 via APCVD method by controlling the S/MoO3 mass ratio and other growth parameters were studied. MoO3 and S were used as precursors.Firstly, the S/MoO3 mass ratio was set to be 2:1 to 8:1, while sulphur powder was placed into a small bushing and mildly sublimated at 105 oC with independently temperaturecontrollable heating belts. Growth substrates were placed face-down above MoO3 at the center of the furnace. MoS2/ MoO2 rhombohedral flakes were synthesized at 950 oC for 5 min. The effects of the setting position of substrates and the flow rate of argon on the morphology of the as-grown products were carefully investigated. By controlling the sulfuration time, few-layer MoS2/MoO2, multilayer MoS2/MoO2 and multilayer MoS2 rhombohedral flakes can be produced, respectively.Secondly, the S/MoO3 mass ratio was increased to be 10:1 to 20:1, while sulphur powder was placed in a ceramic boat and mildly sublimated at 120 oC with independently temperature-controllable heating belts. Growth substrates were placed face-up back to MoO3 at the center of the furnace. Monolayer or few-layer MoS2 triangular flakes were synthesized at 700 oC or 800 oC for 60 min. This method has a wide application range from smooth surface to rough surface. Raising the growth temperature is conducive to increase the size of MoS2 triangular flakes and its coverage. From PL spectra, indirect band gap of monolayer MoS2 is between 1.80 to 1.86 eV.Thirdly, the S/MoO3 mass ratio was set to be 10:1 to 70:1. MoS2 composite structures consisting of edge-oriented MoS2 nanopetals and basal-oriented MoS2 thin films were synthesized at 650-950 oC for 5-120 min. This method is very simple without rigorous condition, and has a high probability of success. By carefully investigating the roles of growth time, temperature and S/MoO3 mass ratio on the morphology and density of the as-grown products, the ideal conditions for growing thinner, high-density MoS2 nanopetals should be at 800 oC for 60 min with S/MoO3 mass ratio to be 30:1.Finally, under the ideal conditions for growing high-density MoS2 nanopetals, MoS2 nanopetals were directly grown on the CNT films. The freestanding, flexible and durable MoS2/CNT composites, used directly as working electrodes, showed remarkable and stable electrocatalytic activity in the hydrogen evolution reaction(HER), as manifested with the low onset overpotential of 100 mV and the small Tafel slope of 49.5 mV per decade, in 0.5 M H2SO4 solutions. Moreover, the MoS2/CNT electrodes exhibit good stability with negligible current loss(2.3%) after 24 h immersion and 100 cycles of the durability test. Importantly, the development of the MoS2/CNT electrode provides a promising way to fabricate other multifunctional electrodes.