Synthesis And Optical Properties Of Monolayer Molybdenum Disulfide

MoS2has been widespread studied as one of advanced solid-state lubricants and catalysts,. In recent years, with the investigation of two-dimensional materials represented by graphene, MoS2has attracted people’s attention since its a series of outstanding properties. Especially it owns an about1.8eV direct band gap for a single layer MoS2, which makes up the deficiency of graphene. In this paper, we focus on exploring a best condition to grow monolayer MoS2by chemical vapor deposition (CVD) method, and researching the effect on the Raman and Photoluminescence (PL) spectra when annealing in different atmosphere or transferring to different substrates.In chapter1, we systematically introduced the basic properties of MoS2, including the crystal structure, electronic structure and optical property. The applications of grapheme-like MoS2in the areas of field effect transistor, sensor, battery electrode materials and Valleytronics are also summarized in this chapter. Meanwhile, we reviewed common synthesis methods of grapheme-like MoS2, including the "top-down" method represented by mechanical exfoliation method and lithium intercalation, and the "bottom-up" synthetic method represented by chemical vapor deposition.In chapter2, we introduced the reagents and instruments used in experiments. And we also introduce several characterization methods of layered MoS2in detail, including optical microscope, Atomic force microscopy, Raman spectroscopy and so on.In chapter3, we explored a best condition growth conditions to prepare monolayer MoS2on SiO2/Si by chemical vapor deposition, these conditions refers to eight aspects including growing temperature, growth atmosphere, growth time, and so on. Meanwhile, related characterization was conducted.In chapter4, the prepared monolayer MoS2was annealed in different atmosphere. After annealing at350℃for30min in a rough vacuum, there are numerous defects and dangling bonds on MoS2surface, on which O2/H2O can adsorb and deplete excess free electrons. Therefore, it switches the optical transition process from trion recombination to exciton recombination, resulting in blue shift～40meV of PL peak. And the dramatic enhancement of PL intensity was attributed to two reasons. Firstly, the sheet density of equilibrium electrons is much depleted by the charge transfer, leading to the repression of nonradiative recombination process. The second one is a lot of defects on monolayer MoS2surface can easily bonded with free electrons and transfer trions to form localized neutral excitons.Finally, we prepared monolayer MoS2with high quality on sapphire, quartz and SiO2/Si substrate by chemical vapor deposition, and then transfer the sample grown on SiO2/Si substrate to a new SiO2/Si substrate and gold film. The PL and Raman characteristic peaks are different after transferring to a new SiO2/Si compared with as-grown sample, which attributed to that the strain is released after transferring. However, it is considered that the changes of PL and Raman spectra of sample transferred on gold film are caused by the p-doping of gold in MoS2layers.