Plasmon–Exciton Interactions in Nanometer-Thick Gold-WSe₂ Multilayer Structures: Implications for Photodetectors, Sensors, and Light-Emitting Devices

Abstract

Van der Waals materials such as thin films of transition-metal dichalcogenides (TMDCs) manifest strongly bound exciton states in the visible spectrum at ambient conditions that provide an ideal platform for exciton−photon couplings. Utilizing nanometer-thick semiconducting TMDCs in the form of multilayer structures combined with metals can increase significantly the light−matter interaction. In this way, the interaction between excitons and surface-plasmon polaritons emerges as a platform for transferring the electromagnetic energy at confined modal volumes. Here, we theoretically investigate how moving electrons can be used as probes of hybrid exciton− plasmon polaritons of gold-WSe 2 multilayers within the context of electron energy-loss spectroscopy and cathodoluminescence spectroscopy. Interestingly, and in contrast to WSe 2 slab waveguides where quasi-propagating photonic modes interact with only exciton A, in gold-WSe 2 multilayers, exciton A and exciton B can both strongly interact with surface-plasmon polaritons. Hence, we observe CL emission suppression at excitonic or plasmonic peaks, which reveals the energy transfer between excitons and plasmons in the form of nonradiating guided waves. Our work provides a systematic study for deeper understanding of the effect of the configuration and the thickness of layers on the photonic and plasmonic modes and hence on the strength of the coupling between excitons and surface-plasmon polaritons in subwavelength dimensions. Our findings pave the way toward designing efficient photodetectors, sensors, and light-emitting devices based on nanometer-thick metal/semiconductor hybrid materials.

Ultrafast Thermionic Electron Injection Effects on Exciton Formation Dynamics at a van der Waals Semiconductor/Metal Interface

“…Heterojunctions of metals and semiconducting transition metal dichalcogenides (TMDs) allow various possibilities for the manipulation and exploitation of light–matter interactions, such as the control of plasmonic excitations − and plasmon-induced charge injection, − transistors, and photovoltaics . Due to their layered structure, excited electrons and holes in TMDs exhibit enhanced Coulomb interactions in both monolayer and bulk (>5 layers) forms, leading to room-temperature stable excitons, which dominate the optical and charge transport properties in these materials.…”

Interaction of excitons with Cherenkov radiation in WSe2 beyond the non-recoil approximation

“…A vector-potential approach is used to calculate the radiation from a moving electron in thin films, e.g. to capture the momentum-resolved electron energy-loss spectroscopy (MREELS) [29][30][31]. The current density of a moving electron with the speed of v el along the z-axis is given by J z (⃗ r, t) = −ev el δ (x) δ (y) δ (z − v el t).…”

Ultrafast control of exciton dynamics by optically-induced thermionic carrier injection in a metal-semiconductor heterojunction

“…In this context, heterojunctions of metals and dielectric materials allow a lot of possibilities for the manipulation and exploitation of light-matter interactions, including ultrafast hot electrons dynamics, magnetooptical effects and nonlinear optical processes 18,[29][30][31][32][33][34][35][36][37][38] . In particular, if the dielectric material is replaced by a semiconducting transition metal dichalcogenide (TMD), we can further boost the control of nanoscale optical excitations [39][40][41][42] , including plasmonic-induced charge injection [43][44][45][46][47][48] , as well as enhance charge dynamics in transistors 49 and photovoltaic devices 50 . Excited electrons and holes in TMDs exhibit enhanced Coulomb interactions in both monolayer and bulk (> 5 layers) forms 51 , leading to room-temperature stable excitons, which dominate the optical and charge transport properties in these materials.…”