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Sub-100 fs Formation of Dark Excitons in Monolayer WS2

Kolesnichenko, Pavel V. LU orcid ; Wittenbecher, Lukas LU ; Zhang, Qianhui ; Teh, Run Yan ; Babu, Chandni LU ; Fuhrer, Michael S. ; Mikkelsen, Anders LU and Zigmantas, Donatas LU orcid (2024) In Nano Letters 24(46). p.14663-14670
Abstract

Two-dimensional semiconducting transition metal dichalcogenides are promising materials for optoelectronic applications due to their strongly bound excitons. While bright excitons have been thoroughly scrutinized, dark excitons have been much less investigated, as they are not directly observable with far-field spectroscopy. However, with their nonzero momenta, dark excitons are significant for applications requiring long-range transport or coupling to external fields. We access such dark excitons in WS2 monolayer using transient photoemission electron microscopy with subdiffraction limited spatial resolution (75 nm) and exceptionally high temporal resolution (13 fs). Image time series of the monolayer are recorded at several... (More)

Two-dimensional semiconducting transition metal dichalcogenides are promising materials for optoelectronic applications due to their strongly bound excitons. While bright excitons have been thoroughly scrutinized, dark excitons have been much less investigated, as they are not directly observable with far-field spectroscopy. However, with their nonzero momenta, dark excitons are significant for applications requiring long-range transport or coupling to external fields. We access such dark excitons in WS2 monolayer using transient photoemission electron microscopy with subdiffraction limited spatial resolution (75 nm) and exceptionally high temporal resolution (13 fs). Image time series of the monolayer are recorded at several different fluences. We directly observe the ultrafast formation of dark K-Λ excitons occurring within 14-50 fs and follow their subsequent picosecond decay. We distinguish exciton dynamics between the monolayer’s interior and edges and conclude that the picosecond-scale evolution of dark excitations is defect-mediated while intervalley scattering is not affected by the defects.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
2D materials, excitons, femtosecond, microscopy, monolayers, photoemission
in
Nano Letters
volume
24
issue
46
pages
8 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:39516189
  • scopus:85209390090
ISSN
1530-6984
DOI
10.1021/acs.nanolett.4c03807
language
English
LU publication?
yes
id
b9ea6661-efa0-4d36-98ef-79017afeac32
date added to LUP
2025-01-15 14:25:25
date last changed
2025-01-29 15:52:36
@article{b9ea6661-efa0-4d36-98ef-79017afeac32,
  abstract     = {{<p>Two-dimensional semiconducting transition metal dichalcogenides are promising materials for optoelectronic applications due to their strongly bound excitons. While bright excitons have been thoroughly scrutinized, dark excitons have been much less investigated, as they are not directly observable with far-field spectroscopy. However, with their nonzero momenta, dark excitons are significant for applications requiring long-range transport or coupling to external fields. We access such dark excitons in WS<sub>2</sub> monolayer using transient photoemission electron microscopy with subdiffraction limited spatial resolution (75 nm) and exceptionally high temporal resolution (13 fs). Image time series of the monolayer are recorded at several different fluences. We directly observe the ultrafast formation of dark K-Λ excitons occurring within 14-50 fs and follow their subsequent picosecond decay. We distinguish exciton dynamics between the monolayer’s interior and edges and conclude that the picosecond-scale evolution of dark excitations is defect-mediated while intervalley scattering is not affected by the defects.</p>}},
  author       = {{Kolesnichenko, Pavel V. and Wittenbecher, Lukas and Zhang, Qianhui and Teh, Run Yan and Babu, Chandni and Fuhrer, Michael S. and Mikkelsen, Anders and Zigmantas, Donatas}},
  issn         = {{1530-6984}},
  keywords     = {{2D materials; excitons; femtosecond; microscopy; monolayers; photoemission}},
  language     = {{eng}},
  month        = {{11}},
  number       = {{46}},
  pages        = {{14663--14670}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Nano Letters}},
  title        = {{Sub-100 fs Formation of Dark Excitons in Monolayer WS<sub>2</sub>}},
  url          = {{http://dx.doi.org/10.1021/acs.nanolett.4c03807}},
  doi          = {{10.1021/acs.nanolett.4c03807}},
  volume       = {{24}},
  year         = {{2024}},
}