Fig. 1: Near-field probing and optical characterization of plexciton emission in a coupled WSe₂–Au-nanotrench system.

a Schematic representation of the device, featuring a WSe₂ monolayer (not to scale) deposited on a gold nanotrench coated with an \(\approx\) 2-nm-thick Al₂O₃ layer. The emitted light is collected using a sharp pyramidal probe (tip curvature radius of 20 nm) integrated into fiber facets (see Supp. Sec. S2 for additional details). b Cross-sectional view (red plane in a) of the plasmon field intensity enhancement in the bare trench. c Energy-level diagram illustrating the plexciton system, with the thick-red arrow denoting plexciton emission primarily originating from the lower polariton (LP), and with the thin-dark arrow representing the emission of the bare (uncoupled) TMD exciton. d Reflection spectrum as a function of incident-light polarization angle (0° to 90° for perpendicular-to-parallel to the trench). Each curve is normalized relative to measurements on the unpatterned substrate. e Photoluminescence spectra acquired with our fiber-based pyramidal probe at positions 1–3 indicated in inset (scale bar is 200 nm).