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Reduced Binding Energy and Layer-Dependent Exciton Dynamics in Monolayer and Multilayer WS2
journal contribution
posted on 2019-12-13, 21:13 authored by Yuanshuang Liu, Xiangmin Hu, Ting Wang, Dameng LiuThe exciton dynamics in WS2 from monolayer
to four-layer
was investigated by using fluorescence lifetime imaging measurement
(FLIM). The transition process of negatively charged trions is measured
and detected using a fluorescence detection method. Compared with
neutral excitons, negatively charged trions have a longer fluorescence
lifetime. Further exploration illustrated that the fluorescence lifetime
of both neutral excitons and trions get longer when the thickness
increased. When WS2 was added from monolayer to four-layer,
lifetimes of direct transition excitons and trions tended to increase
over 10 and 2.5 times, separately, whereas the lifetime of indirect
transition excitons tended to be reduced by nearly 2.5 times. This
layer-dependent signature is ascribed to the reduced binding energy
in thicker WS2 at room temperature, which is verified by
density theory functional calculation. Although the direct transition
exciton dominates the whole fluorescence decay process, it is influenced
by trions and dark excitons. Based on the FLIM results, we proposed
four main exciton transition channels during the fluorescence luminescence
process. Such layer-dependent transition channel conception helps
to control the fluorescence lifetime, which determines the efficiency
of the carriers’ separation.
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fluorescence luminescence processWS 2fluorescence lifetimeLayer-Dependent Exciton Dynamicstransition excitonsfluorescence detection methodFLIM2.5 timesMultilayer WS 2Such layer-dependent transition channel conceptionfluorescence lifetime imaging measurementReduced Binding Energyexciton transition channelstrionfluorescence decay process
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