Plasmonic radial breathing mode (RBM), featured with radially oscillating charge density, arises from the surface plasmon waves confined in the flat nanoparticles. The zero net dipole moment endows the RBM with an extremely low radiation yet a remarkable intense local field. On the other hand, owing to the dark mode nature, the RBMs routinely escape from the optical measurements, severely preventing their applications in optoelectronics and nanophotonics. Here, we experimentally demonstrate the existence of RBM in a hexagonal Au nanoplate-on-mirror nanocavity using a far-field linear-polarized light source. The polarization-resolved scattering measurements cooperated with the full-wave simulations elucidate that the RBM originates from the standing plasmon waves residing in the Au nanoplate. Further numerical analysis shows the RBM possesses the remarkable capability of local field enhancement over the other dark modes in the same nanocavity. Moreover, the RBM is sensitive to the gap and nanoplate size of the nanocavity, providing a straightforward way to tailor the wavelength of RBM from the visible to near-infrared region. Our approach provides a facile optical path to access to the plasmonic RBMs and may open up a new route to explore the intriguing applications of RBM, including surface-enhanced Raman scattering, enhanced nonlinear effects, nanolasers, biological and chemical sensing.
Plasmonic particle-on-film nanocavities, supporting gap modes with ultra-small volume, provide a great solution to boost light–matter interactions at the nanoscale. In this work, we report on the photoluminescence (PL) enhancement of monolayer MoS 2 using high order modes of an Au nanosphere dimer-on-film nanocavity (DoFN). The high order plasmon modes, consisting of two bonding quadrupoles in the dimer and their images in the Au film, are revealed by combining the polarization-resolved scattering spectra with the numerical simulations. Further integrating the monolayer MoS 2 into the DoFN, these high order modes are used to enhance PL intensity through simultaneously boosting the absorption and emission processes, producing a 1350-fold enhancement factor. It opens an avenue to enhance the light–matter interaction with high order plasmon modes and may find applications in future optoelectronics and nanophotonics devices.
Two‐dimensional transition metal dichalcogenides exhibit remarkable optical properties. However, their applications in electronics and photonics are severely limited by the intrinsically low absorption and emission rates. Here, the photoluminescence (PL) enhancement by integrating the monolayer MoSe2 into an Ag nanowire‐on‐mirror (NWoM) nanocavity is reported. From the dark‐field scattering spectrum, a Fano resonance resulting from the coupling between discrete exciton state of MoSe2 and broad plasmon mode of nanocavity is observed. This Fano resonance, as a characteristic of intermediate plasmon–exciton coupling, shows remarkable ability to accelerate emission rate of MoSe2. Furthermore, the nanocavity with multiple resonances provides an excellent spatial mode overlap at excitation and emission wavelengths that affords the intriguing opportunity to resonantly enhance the absorption and PL quantum yield at the same location. The combination of Fano resonance and mode matching allows the attainment of over 1800‐fold PL enhancement. These results provide a facile way to enhance the PL intensity of monolayer MoSe2 that may facilitate highly efficient optoelectronic devices.
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