Identifying Excitation and Emission Rate Contributions to Plasmon-Enhanced Photoluminescence from Monolayer MoS₂ Using a Tapered Gold Nanoantenna

Single-element and periodic arrays of plasmonic nanoantennas have been used to enhance light-matter interactions in 2D materials to improve their suitability for optoelectronic devices. However, single nanoantennas with discrete resonances do not readily enable separation of enhancements in excitation and emission, each of which influences total Raman and photoluminescence (PL) enhancement. Here we use a single Au tapered plasmonic nanoantenna with optical resonances that extend above and below the band gap to observe a broad enhancement in PL of MoS₂. The largest peak enhancement of ∼3.2 is observed at an antenna position between the position of maximum excitation-field enhancement and the position of maximum Purcell factor, indicating a contribution of both excitation and emission rate enhancements. In contrast, the peak Raman enhancement occurs at the position of the excitation-field maximum because it is only dependent on the enhancement of the electric field. This independent determination of excitation and emission rate enhancements via spatial separation provides a more comprehensive picture of light-matter interactions in MoS₂ monolayers interfaced with plasmonic materials.