Ultrafast Pump-probe Transient Absorption Spectroscopy of Layer-controllable Molybdenum Disulfide Films

• Main Authors: Yung-Hung Huang, 黃永鴻
• Other Authors: Yi-Jia Chen
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/qe5ha2

碩士 === 國立東華大學 === 材料科學與工程學系 === 107 === In this thesis, we focus on the ultrafast dynamics of layer-controllable molybdenum disulfide films by using the pump-probe transient absorption technique. In addition, we compare the different fabrication process of molybdenum disulfide films. We verify the optical selection rule in molybdenum disulfide films by change the polarization properties of pump. In the first chapter, we introduce the recently research in two-dimensional material and include the molybdenum disulfide, which is in the family of the two-dimensional transition metal dichalcogenides. Next chapter, we introduce the ultrafast dynamics in the semiconductor and the two-dimensional transition metal dichalcogenides. The third part, we explain what is the pump-probe transient absorption technique and show the equipment used in all experiments. The fourth part is about the experiment result and discussion. Moreover, the final part, we conclude our study of the ultrafast pump-probe transient absorption spectroscopy of layer-controllable molybdenum disulfide films. Then, we observed the five characteristic peaks of molybdenum disulfide, the excited absorption, the absorption between A-exciton and B-exciton, and the interband absorption results from the defect and impurities, A-exciton, B-exciton, from the measurement of the transient absorption spectroscopy. The lifetime τfast of monolayer molybdenum disulfide is in the range of 30 ps and the lifetime τslow is between 20~60 ps. With the increasing layer number of molybdenum disulfide from monolayer to five layers, the range of lifetime τfast and lifetime τslow are increased to 120 ps and 350 ps respectively, which explains the results throughout the timescale of non-thermal regime, hot-carrier regime and isothermal regime but would substantially complicate the analysis of collected signals. Therefore, we could only say that the lifetime of excited absorption and interband absorption are increasing with the increasing layer number of molybdenum disulfide. Finally, the signals of the five layers molybdenum disulfide is changed obviously by the circular polarization of Pump than other samples, which explained that we may consider the effect of phonon under room temperature or the condition of the circular polarization of Probe.