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Title: Ultrafast Electron and Hole Relaxation Pathways in Few-Layer MoS2
Authors: Nie, Zhaogang
Long, Run
Teguh, Jefri S.
Huang, Chung-Che
Hewak, Daniel W.
Yeow, Edwin K. L.
Shen, Zexiang
Prezhdo, Oleg V.
Loh, Zhi-Heng
Keywords: DRNTU::Science::Chemistry
Issue Date: 2015
Source: Nie, Z., Long, R., Teguh, J. S., Huang, C.-C., Hewak, D. W., Yeow, E. K. L., et al. (2015). Ultrafast Electron and Hole Relaxation Pathways in Few-Layer MoS2. The Journal of Physical Chemistry C, 119(35), 20698-20708.
Series/Report no.: The Journal of Physical Chemistry C
Abstract: Femtosecond optical pump–probe spectroscopy is employed to elucidate the band-selective ultrafast carrier dynamics of few-layer MoS2. Following narrowband resonant photoexcitation of the exciton A transition, the subpicosecond to picosecond relaxation dynamics of the electron and the hole at the K valley are separately interrogated by a broadband probe pulse. The temporal evolution of the spectral first moment reveals nonexponential intravalley relaxation dynamics in the conduction band. Fluence dependence measurements suggest that this relaxation process is predominantly mediated by acoustic phonon emission. Intervalley scattering of carriers from the K valley to the extrema of the conduction and valence bands is also observed via the decay of the spectral zeroth moment. In addition, second-order Raman scattering leads to the emergence of sidebands in the normalized differential transmission spectra. The observed two-phonon energies and the fluence-dependent time constants suggest that the E1g longitudinal optical (LO) phonon and the LA phonon participate in intervalley scattering in the conduction and valence bands, respectively. Ab initio nonadiabatic molecular dynamics simulations yield time constants of 0.80 and 0.72 ps for intra- and intervalley electronic relaxation, respectively; the latter agrees well with experiment. Finally, the normalized differential transmission spectra reveal a two-electron shake-up satellite that originates from band-edge radiative recombination and the simultaneous excitation of a hole from Kv1 to Kv2. From its spectral position, a Kv1–Kv2 spin–orbit splitting of 1166 ± 1 cm–1 is deduced. The observation of the two-electron transition points to the existence of strong electron correlation in photoexcited few-layer MoS2.
ISSN: 1932-7447
DOI: 10.1021/acs.jpcc.5b05048
Schools: School of Materials Science & Engineering 
School of Physical and Mathematical Sciences 
Rights: © 2015 American Chemical Society. This is the author created version of a work that has been peer reviewed and accepted for publication by The Journal of Physical Chemistry C, American Chemical Society. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [].
Fulltext Permission: open
Fulltext Availability: With Fulltext
Appears in Collections:MSE Journal Articles
SPMS Journal Articles

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