期刊
ACS NANO
卷 7, 期 2, 页码 1072-1080出版社
AMER CHEMICAL SOC
DOI: 10.1021/nn303973r
关键词
MoS2; atomically thin 2D crystal; exciton dynamics transient absorption spectroscopy; transient absorption microscopy; quantum confinement; surface defects
类别
资金
- Division of Chemical Sciences, Geosciences and Biosciences, Basic Energy Sciences, Office of Science, United States Department of Energy [DE-FC02-04ER15533]
- Sustainable Energy Initiative of University of Notre Dame
- Air Force Office of Scientific Research [FA9550-12-1-0257]
- National Science Foundation [NSF-ECCS 1232191]
- NSF CAREER award
- Swiss National Science Foundation [200021_132102]
- Swiss Nanoscience Institute (NCCR Nanoscience)
- European Research Council [240076]
- Swiss National Science Foundation (SNF) [200021_132102] Funding Source: Swiss National Science Foundation (SNF)
- Directorate For Engineering
- Div Of Electrical, Commun & Cyber Sys [1232191] Funding Source: National Science Foundation
Femtosecond transient absorption spectroscopy and microscopy were employed to study exciton dynamics in suspended and Si3N4 substrate-supported monolayer and few-layer MoS2 2D crystals. Exciton dynamics for the monolayer and few-layer structures were found to be remarkably different from those of thick crystals when probed at energies near that of the lowest energy direct exciton (A exciton). The intraband relaxation rate was enhanced by more than 40 fold in the monolayer in comparison to that observed in the thick crystals, which we attributed to defect assisted scattering. Faster electron-hole recombination was found in monolayer and few-layer structures due to quantum confinement effects that lead to an indirect-direct band gap crossover. Nonradiative rather than radiative relaxation pathways dominate the dynamics in the monolayer and few-layer MoS2. Fast trapping of excitons by surface trap states was observed in monolayer and few-layer structures, pointing to the importance of controlling surface properties in atomically thin crystals such as MoS2 along with controlling their dimensions.
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