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Raman scattering excitation (RSE) is an experimental technique in which the spectrum is made up by sweeping the excitation energy when the detection energy is fixed in resonance with an excitonic transition. We study the low-temperature (T=5 K) RSE spectra measured on four high quality monolayers (ML) of semiconducting transition metal dichalcogenides (S-TMDs), i.e. MoS2, MoSe2, WS2, and WSe2, encapsulated in hexagonal BN. The outgoing resonant conditions of Raman scattering reveal an extraordinary intensity enhancement of the phonon modes, which results in extremely rich RSE spectra. The obtained spectra are composed not only of Raman-active peaks, i.e. in-plane E′ and out-of-plane A′1, but the appearance of 1st, 2nd, and higher-order phonon modes is recognised. We find that the intensity profiles of the A′1 modes in the investigated MLs resemble the emissions due to neutral excitons measured in the corresponding PL spectra for the outgoing type of resonant Raman conditions. Furthermore, for the WSe2 ML, the A′1 mode was observed in resonance of the incoming light with the neutral exciton line. The strength of the exciton-phonon coupling (EPC) in S-TMD MLs strongly depends on the type of their ground excitonic state, i.e. bright or dark, resulting in different shapes of the RSE spectra. Our results demonstrate that RSE spectroscopy is a powerful technique for studying EPC in S-TMD MLs.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Raman scattering excitation, semiconducting TMDs, exciton-phonon coupling

Date published: 2024-01-10

Publisher: Springer Science and Business Media LLC

Journal:

• npj 2D Materials and Applications (ISSN: 23977132) vol. 8 issue. 1 2

Funding:

• Narodowe Centrum Nauki 2018/31/B/ST3/02111
• Narodowe Centrum Nauki 2017/27/B/ST3/00205
• Narodowe Centrum Nauki 2017/27/B/ST3/00205
• Grantová Agentura České Republiky 23-05578S
• Narodowe Centrum Nauki 2021/41/B/ST3/04183
• MEXT | Japan Society for the Promotion of Science 23H02052
• MEXT | Japan Society for the Promotion of Science 23H02052
• European Commission Graphene Flagship Project
• Fundacja na rzecz Nauki Polskiej MAB/2018/9
• Narodowe Centrum Nauki 2017/27/B/ST3/00205

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1038/s41699-023-00438-5

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Updated at: 2025-02-23 22:47:59 +0900

Published on MDR: 2025-02-23 22:47:59 +0900