Study of plexcitons in a metal nanotriangle–WS ₂ composite system using electron energy loss spectroscopy

Strong coupling between plasmons and excitons in transition metal dichalcogenides enables room-temperature plexciton formation, providing a crucial platform for investigating Bose-Einstein condensation, low-threshold nanolasers, and ultrafast optical switches. Plexcitons can be produced by far-field optical excitation and near-field electron beam excitation, while electron beam excitation enables the detection of dark plasmon modes and their spatial imaging. Using the boundary element method with a coupled harmonic oscillator model, electron energy loss spectroscopy of silver nanotriangles, WS₂, and their composite system is simulated. Our numerical results are consistent with the corresponding experiments. From the charge distributions of silver nanotriangles in electron beam excitation, the dipole configurations corresponding to bright and dark plasmon modes are identified. The coupling mechanism of excitons and plasmons in the composite structure is analyzed. Additionally, the origin of asymmetry in spatial imaging maps of electron loss from plexcitons is clarified, and the proportions of plasmons and excitons in plexcitons produced by different detunings are analyzed theoretically. This study provides guidance for further experimental and theoretical research on strong coupling in analogous composite systems.