Quantum plasmonic control of trions in a picocavity with monolayer WS ₂

Abstract

Monitoring and controlling the neutral and charged excitons (trions) in two-dimensional (2D) materials are essential for the development of high-performance devices. However, nanoscale control is challenging because of diffraction-limited spatial resolution of conventional far-field techniques. Here, we extend the classical tip-enhanced photoluminescence based on tip-substrate nanocavity to quantum regime and demonstrate controlled nano-optical imaging, namely, tip-enhanced quantum plasmonics. In addition to improving the spatial resolution, we use the scanning probe to control the optoelectronic response of monolayer WS2 by varying the neutral/charged exciton ratio via charge tunneling in Au-Ag picocavity. We observe trion “hot spots” generated by varying the picometer-scale probe-sample distance and show the effects of weak and strong coupling, which depend on the spatial location. Our experimental results are in agreement with simulations and open an unprecedented view of a new range of quantum plasmonic phenomena with 2D materials that will help to design new quantum optoelectronic devices.

Tip‐Induced Nano‐Engineering of Strain, Bandgap, and Exciton Funneling in 2D Semiconductors

“…Similarly, the TEPL linewidth (FWHM) decreases at the wrinkle from ≈52 to ≈48 meV due to the symmetrically modified spectral shape, as shown in Figure 3b. The asymmetric nature of the TEPL spectrum at the crystal face is attributed to the trion and biexciton shoulders [7,41] and asymmetric phonon sidebands caused by the strong exciton-phonon coupling. [23] Therefore, from the modified spectral shape and the linewidth map, we believe that the exciton PL response is more significantly influenced by the induced tensile strain at the wrinkle compared to the PL responses of trions and biexcitons.…”

Tip-enhanced photoluminescence nano-spectroscopy and nano-imaging

“…Recently, He et al demonstrated the local control of radiative emission of neutral excitons and trions in WS 2 monolayer through precision gap control between Ag tip and Au substrate [149]. Figure 16A shows a schematic illustration of the experimental setup.…”

Adaptive tip-enhanced nano-spectroscopy

“…Figure 3 b shows the spectral evolution of a -TEPL response with respect to the distance between Au tip and the crystal on Au film. a -TEPL gradually increases from d = 10 nm to 5 nm owing to the localized antenna effect of Au tip, and is further enhanced at d < 5 nm by the strong interaction between tip-dipole and image-dipole, which shows a similar behavior to the normal TEPL response 24 , 25 . We then obtain a -TEPL image of a WSe 2 monolayer with the same Au tip to quantify the spatial resolution, which is needed to estimate TEPL enhancement factor.…”