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

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-WSe2 multilayers within the context of electron energy-loss spectroscopy and cathodoluminescence spectroscopy. Interestingly, and in contrast to WSe2 slab waveguides where quasi-propagating photonic modes interact with only exciton A, in gold-WSe2 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.