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STM in the spotlight !

Enhancement of TMD luminescence by plasmonic substrates

par Guy Molénat - publié le , mis à jour le

Luminescence of MoSe2 semiconducting monolayers has been studied by scanning tunneling microscope-induced light emission technique with unprecedented spatial and spectral resolutions. Fundamental mechanisms at the origin of this light emission process have been precisely identified and the luminescence intensity of the monolayers has been enhanced by an order of magnitude by using nanostructured plasmonic substrates.

Integrated optics is a promising way for improving information transmission speed. In the race toward miniaturization, near-field techniques allow to overcome the fundamental barrier of diffraction. In this general context, a transverse team bringing together researchers from three different CEMES groups (NeO, SINanO and GNS) has developped an original experimental setup enabling the study of fundamental light emission mechanisms at unprecedented spatial and spectral resolution scales.

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L’émission de lumière excitée par le courant tunnel dans un STM permet l’étude des mécanismes de luminescence à une échelle nanométrique. Elle est mise à profit pour démontrer l’exaltation de la luminescence de monocouches de MoSe2 sur des substrats plasmoniques nanostructurés.

This so-called STM-induced light emission technique has been applied to the study of the luminescence of MoSe2monolayers deposited on metallic substrates (collaboration with Rice University, Houston and University of Texas, San Antonio). Specific spectral signatures of both the substrate and the MoSe2 monolayer luminescence have been identified. They reveal two distinct fundamental light emission mechanisms : radiative decay of tip-surface gap plasmon modes in the case of a metallic substrate, and electron-hole recombinations in the case of the MoSe2monolayer. Photonic maps show at a nanometer resolution scale that the MoSe2 luminescence emission rate is increased by minority charge carriers creation in the semiconducting monolayer, and allow for a detailed description of the light emission mechanism.

The use of plasmonic substrates to support the MoSe2 monolayers gives birth to a strong coupling between excitons confined in the monolayer, and plasmon modes excited on the substrate surface by tunneling electrons. Substrate morphology appears thus to be a key parameter to tune or de-tune the spectral overlap of these fundamental excitations to modulate this coupling, and in fine the monolayer light emission rate. By using a nanostructured gold substrate, we demonstrate an enhancement by an order of magnitude of light emission intensity of the MoSe2monolayer, compared to the one observed with a flat substrate. This original approach paves the way to novel spectroscopy and imaging techniques for addressing the photon emission from localized emitters such as quantum dots, or molecules.


"Plasmonic-Induced Luminescence of MoSe2 Monolayers in a Scanning Tunneling Microscope"

R. Péchou, S. Jia, J. Rigor, O. Guillermet, G. Seine, J. Lou, N. Large, A. Mlayah, R. Coratger.

ACS Photonics 2020. http://dx.doi.org/10.1021/acsphotonics.0c01101


 Contact : Dr. Renaud Péchou, UPS, CEMES (CNRS) renaud.pechou chez cemes.fr