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Ultrafast electron and hole relaxation pathways in few-layer MoS2

Ultrafast electron and hole relaxation pathways in few-layer MoS2
Ultrafast electron and hole relaxation pathways in few-layer MoS2
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.
0022-3654
20698-20708
Nie, Zhaogang
19d1332d-7678-4ab4-8cb6-850205e69eea
Long, Run
46fdff2a-651b-4a5a-9452-73e4c5119508
Teguh, Jefri S.
15e51e46-f27f-4656-bfb0-d6cdabd70789
Huang, Chung-Che
825f7447-6d02-48f6-b95a-fa33da71f106
Hewak, Daniel
87c80070-c101-4f7a-914f-4cc3131e3db0
Yeow, Edwin K.L.
15bc0e63-08ef-4849-b1ad-8a7c3e801328
Shen, Zexiang
f17e56a3-2976-4d8c-aac0-d7e7422216ed
Prezhdo, Oleg V.
d3493782-364d-492d-b0ec-075991846a63
Loh, Zhi-Heng
a6a84562-e2c1-46d6-9b75-4874a232c52a
Nie, Zhaogang
19d1332d-7678-4ab4-8cb6-850205e69eea
Long, Run
46fdff2a-651b-4a5a-9452-73e4c5119508
Teguh, Jefri S.
15e51e46-f27f-4656-bfb0-d6cdabd70789
Huang, Chung-Che
825f7447-6d02-48f6-b95a-fa33da71f106
Hewak, Daniel
87c80070-c101-4f7a-914f-4cc3131e3db0
Yeow, Edwin K.L.
15bc0e63-08ef-4849-b1ad-8a7c3e801328
Shen, Zexiang
f17e56a3-2976-4d8c-aac0-d7e7422216ed
Prezhdo, Oleg V.
d3493782-364d-492d-b0ec-075991846a63
Loh, Zhi-Heng
a6a84562-e2c1-46d6-9b75-4874a232c52a

Nie, Zhaogang, Long, Run, Teguh, Jefri S., Huang, Chung-Che, Hewak, Daniel, Yeow, Edwin K.L., Shen, Zexiang, Prezhdo, Oleg V. and Loh, Zhi-Heng (2015) Ultrafast electron and hole relaxation pathways in few-layer MoS2. The Journal of Physical Chemistry, 119 (35), 20698-20708. (doi:10.1021/acs.jpcc.5b05048).

Record type: Article

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.

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More information

Published date: 12 August 2015
Organisations: Optoelectronics Research Centre

Identifiers

Local EPrints ID: 381142
URI: https://eprints.soton.ac.uk/id/eprint/381142
ISSN: 0022-3654
PURE UUID: 28a4c550-3994-4e9c-b4b8-56165b68f8d9
ORCID for Chung-Che Huang: ORCID iD orcid.org/0000-0003-3471-2463
ORCID for Daniel Hewak: ORCID iD orcid.org/0000-0002-2093-5773

Catalogue record

Date deposited: 25 Sep 2015 09:14
Last modified: 19 Nov 2019 01:59

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