Exciton Dynamics in Suspended Monolayer and Few-Layer MoS2 2D Crystals

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• 作者：Hongyan Shi ; Rusen Yan ; Simone Bertolazzi ; Jacopo Brivio ; Bo Gao ; Andras Kis ; Debdeep Jena ; Huili Grace Xing ; Libai Huang
• 刊名：ACS Nano
• 出版年：2013
• 出版时间：February 26, 2013
• 年：2013
• 卷：7
• 期：2
• 页码：1072-1080
• 全文大小：505K
• 年卷期：v.7,no.2(February 26, 2013)
• ISSN：1936-086X

文摘

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鈥揾ole recombination was found in monolayer and few-layer structures due to quantum confinement effects that lead to an indirect鈥揹irect 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.

Keywords:

MoS₂; atomically thin 2D crystal; exciton dynamics; transient absorption spectroscopy; transient absorption microscopy; quantum confinement; surface defects