Generation and Detection of Strain-Localized Excitons in WS₂ Monolayer by Plasmonic Metal Nanocrystals

Abstract

Excitons in a transition-metal dichalcogenide (TMDC) monolayer can be modulated through strain with spatial and spectral control, which offers opportunities for constructing quantum emitters for applications in onchip quantum communication and information processing. Strain-localized excitons in TMDC monolayers have so far mainly been observed under cryogenic conditions because of their subwavelength emission area, low quantum yield, and thermal-fluctuation-induced delocalization. Herein, we demonstrate both generation and detection of strain-localized excitons in WS 2 monolayer through a simple plasmonic structure design, where WS 2 monolayer covers individual Au nanodisks or nanorods. Enhanced emission from the strain-localized excitons of the deformed WS 2 monolayer near the plasmonic hotspots is observed at room temperature with a photoluminescence energy redshift up to 200 meV. The emission intensity and peak energy of the strain-localized excitons can be adjusted by the nanodisk size. Furthermore, the excitation and emission polarization of the strain-localized excitons are modulated by anisotropic Au nanorods. Our results provide a promising strategy for constructing nonclassical integrated light sources, high-sensitivity strain sensors, or tunable nanolasers for future dense nanophotonic integrated circuits.

Celebrating 60 Years of The Chinese University of Hong Kong: Research Highlights in Nanoscience and Nanotechnology

“…The thickness of the SiO 2 layer is ∼300 nm. Reprinted from ref . Copyright 2022 American Chemical Society.…”

“…When circular Au nanodisks are covered with a piece of WS 2 monolayer, the WS 2 monolayer bends down at the edge of the nanodisk (Figure c). As a result, local strain is induced on the WS 2 monolayer at the nanodisk edge position . Because the position of the localized strain in the WS 2 monolayer and that of the localized electric field enhancement induced by the nanodisk spatially overlap with each other, the emissions from the strain-localized excitons are amplified by the localized plasmons of the nanodisk and can be detected at room temperature.…”

“…As a result, local strain is induced on the WS 2 monolayer at the nanodisk edge position. 27 Because the position of the localized strain in the WS 2 monolayer and that of the localized electric field enhancement induced by the nanodisk spatially overlap with each other, the emissions from the strain-localized excitons are amplified by the localized plasmons of the nanodisk and can be detected at room temperature. The Au nanodisk, therefore, plays two roles in this simple structure.…”

Unusual Defect-Related Room-Temperature Emission from WS2 Monolayers Synthesized through a Potassium-Based Precursor

“…28,29 Interestingly, while experiments have often required cryogenic temperatures for detection�although their emission from WS 2 bilayers was seen up to around 180 K 30 �this has been extended to room temperature through postsynthetic patterning 31 or substrate-induced strain and plasmonic enhancement. 32 Beyond this, heterogeneities also provide a further framework for modifying or tuning other phenomena. Defects are known to lower the photoluminescent quantum yield and carrier mobility in pristine devices.…”

“…In both phases, many properties are further determined by the presence and distribution of defects and inhomogeneities within the layer. − One example is the trapping of excitons. − Such localized excitons are of increasing research focus as potential sites for single-photon emission, , as well as in quantum information, and valleytronics. , Interestingly, while experiments have often required cryogenic temperatures for detectionalthough their emission from WS 2 bilayers was seen up to around 180 Kthis has been extended to room temperature through postsynthetic patterning or substrate-induced strain and plasmonic enhancement …”