title: Exciton dynamics in suspended monolayer and few-layer MoS₂ 2D crystals.
abstract: 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.
authors.affiliation: Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Shi
authors.forename: Rusen
authors.initials: R
authors.lastname: Yan
authors.forename: Simone
authors.initials: S
authors.lastname: Bertolazzi
authors.forename: Jacopo
authors.initials: J
authors.lastname: Brivio
authors.forename: Bo
authors.initials: B
authors.lastname: Gao
authors.forename: Andras
authors.initials: A
authors.lastname: Kis
authors.forename: Debdeep
authors.initials: D
authors.lastname: Jena
authors.forename: Huili Grace
authors.initials: HG
authors.lastname: Xing
authors.forename: Libai
authors.initials: L
authors.lastname: Huang