Measurement of Ultrafast Excitonic Dynamics of Few-Layer MoS2 Using State-Selective Coherent Multidimensional Spectroscopy

详细信息    查看全文

• 作者：Kyle J. Czech ; Blaise J. Thompson ; Schuyler Kain ; Qi Ding ; Melinda J. Shearer ; Robert J. Hamers ; Song Jin ; John C. Wright
• 刊名：ACS Nano
• 出版年：2015
• 出版时间：December 22, 2015
• 年：2015
• 卷：9
• 期：12
• 页码：12146-12157
• 全文大小：1137K
• ISSN：1936-086X

文摘

We report the first coherent multidimensional spectroscopy study of a MoS₂ film. A four-layer sample of MoS₂ was synthesized on a silica substrate by a simplified sulfidation reaction and characterized by absorption and Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. State-selective coherent multidimensional spectroscopy (CMDS) on the as-prepared MoS₂ film resolved the dynamics of a series of diagonal and cross-peak features involving the spin鈥搊rbit split A and B excitonic states and continuum states. The spectra are characterized by striped features that are similar to those observed in CMDS studies of quantum wells where the continuum states contribute strongly to the initial excitation of both the diagonal and cross-peak features, while the A and B excitonic states contributed strongly to the final output signal. The strong contribution from the continuum states to the initial excitation shows that the continuum states are coupled to the A and B excitonic states and that fast intraband relaxation is occurring on a sub-70 fs time scale. A comparison of the CMDS excitation signal and the absorption spectrum shows that the relative importance of the continuum states is determined primarily by their absorption strength. Diagonal and cross-peak features decay with a 680 fs time constant characteristic of exciton recombination and/or trapping. The short time dynamics are complicated by coherent and partially coherent pathways that become important when the excitation pulses are temporally overlapped. In this region, the coherent dynamics create diagonal features involving both the excitonic states and continuum states, while the partially coherent pathways contribute to cross-peak features.