Monolayer Molybdenum Disulfide Modified By Small Organic Molecules And The Optoelectronic Properties Study

Since monolayer graphene was exfoliated by Geim in 2004, two dimensional materials have been developed rapidly in recent years. Graphene like semiconductor materials, such as molybdenum disulfide(MoS2), when the thickness decreased from bulk to monolayer will show many special optoelectronic properties. But in recent studies, due to the limitation of its intrinsic low mobility, optoelectronic properties, pristine MoS2 were not satisfied for harsh requirement in practical application. Some functionalization methods have been developed to control the optoelectronic properties of MoS2. In this thesis we discuss the growth conditions of chemical vapor deposition of single layer crystal MoS2 and the optoelectronic properties of dye-sensitized MoS2.We utilized CVD method to fabricate triangular single layer MoS2 nanosheets. In experimental process we focus on conditions such as temperature, carrier gas flow rate, the amount of reactants, distance between reactants and Si/SiO2 substrate. It is found that the atomic layer MoS2 shows the highest quality at the condition of 700 oC, 25 min, 15 sccm, 40 mg MoO3, and 4 cm distance.Taking into account, the effects of molecular structures and absorption bandwidth of organic molecules, 3 kinds of dyes including methyl orange, Rhodamine 6G and methylene blue were utilized to sensitize MoS2 photodetector. We found that the sensitized MoS2 photodetectors showed excellent photoresponsitivity of 3.73 A/W, 1.49 A/W, or 10.87 A/W respectively. And the photocurrents of the sensitized MoS2 photodetector can be enhanced about 8, 11 and 20 times, respectively. We further tested the bias and light intensity effects on dye sensitized MoS2 photodetector, showing high stability under different light intensity. The enhanced optoelectronic performance suggested that dye is a good modifier to improve the performance of pristine MoS2 photodetector.In order to explore the mechanism of dye sensitized MoS2 photodetector, we conducted a series of experiments. Photoinduced transfer measurements of the pristine MoS2 and dye modified MoS2 indicated the n-doping effect of dye molecules on the MoS2. Additionally, surface enhanced Raman measurements also confirmed the direct correlation with charge transfer between organic dyes and MoS2, taking into account the chemically enhanced Raman scattering mechanism. The flat molecular structure of MB and S-S or S-Mo interactions are favourable to enhance the photocurrent under light illunination, because of the effective photoinduced electron transfer from the LUMO level of MB to the conduction band of MoS2, thus leading to the highest adjusting ability in terms of the optical performance of the dye/MoS2 hybrid photodetectors among all tested dyes. Present work provides a new clue for the manipulation of high-performance of twodimensional(2D) layered semiconductor based photodetector via the combination of organic dyes.