Ultrafast Dynamics in Single Layer Molybdenum Disulfide
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Molybdenum disulfide, a transition metal dichalcogenide (TMD), has a direct band gap of 1.89 eV when thinned down to a single molecular layer. Exciton recombination pathways and lifetimes have been previously studied, but a consensus has not yet been reached on the physical origins of the reported lifetimes, which range from 2 ps to 10 ns. We study the excitonic properties of a particular TMD, MoS2. We conduct photoluminescence experiments to characterize the number of layers in our samples, and understand their exciton recombination pathways. We observe PL that is non-linearly dependent on pump fluence, which we attribute to exciton-exciton annihilations. We use a technique that is novel to single layer TMDs, femtosecond excitation correlation spectroscopy (FEC), which exploits the non-linear pump-power dependence. With FEC, we extract exciton-exciton annihilation rates in the high exciton density regime, and a decay rate for lower density regimes. We obtain a low density decay rate of Γ = 0.18 ± 0:02 1/ps, and an exciton-exciton annihilation rate of Γₙₗ = 2.4 ± 0.4 nm²/ps.
URI for this recordhttp://hdl.handle.net/1974/26521
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