Modal strong coupling between localized surface plasmon resonance and a Fabry–Pérot nanocavity has been studied to improve the quantum efficiency of artificial photosynthesis. In this research, we employed Au nanodisk/titanium dioxide/Au film modal strong coupling structures to investigate the mechanism of quantum efficiency enhancement. We found that the quantum coherence within the structures enhances the apparent quantum efficiency of the hot-electron injection from the Au nanodisks to the titanium dioxide layer. Under near-field mapping using photoemission electron microscopy, the existence of quantum coherence was directly observed. Furthermore, the coherence area was quantitatively evaluated by analyzing the relationship between the splitting energy and the particle number density of the Au nanodisks. This quantum-coherence-enhanced hot-electron injection is supported by our theoretical model. Based on these results, applying quantum coherence to photochemical reaction systems is expected to effectively enhance reaction efficiencies.

We fabricated a plasmon–nanocavity coupling structure composed of Au nanoparticles (Au-NPs), titanium dioxide, and Au-film (ATA) as a highly sensitive and spatially homogeneous surface-enhanced Raman scattering (SERS) substrate. The SERS intensity of the ATA was ∼11 times higher than that of the Au-NPs/TiO2 substrates without cavity enhancement. This SERS enhancement was attributed to the remarkable near-field enhancement of Au-NPs under coupling with cavity resonance. Under the present experimental conditions, crystal violet (CV) molecule decorated ATA prepared from a concentration as low as 10–7 mol/L could be detected, which is 1 order of magnitude higher sensitivity than the samples without cavities. More importantly, a spatially homogeneous SERS signal distribution of Raman mapping on the ATA was demonstrated over a 20 × 20 μm2 area on the sample, attributed to the homogeneous near-field distribution over the Au-NPs under coherent coupling between plasmon resonance and cavity resonance. We envision that this plasmon–nanocavity coupling SERS structure with high sensitivity, repeatability, and spatial homogeneity can be practically used in chemical and biomolecule detection devices.

The ability to control the motion of single nanoparticles or molecules is currently one of the major scientific and technological challenges. Despite tremendous progress in the field of plasmonic nanotweezers, controlled nanoscale manipulation of nanoparticles trapped by a plasmonic nanogap antenna has not been reported yet. Here, we demonstrate the controlled orbital rotation of a single fluorescent nanodiamond trapped by a gold trimer nanoantenna irradiated by a rotating linearly polarized light or circularly polarized light. Remarkably, the rotation direction is opposite to the light's polarization rotation. We numerically show that this inversion comes from sequential excitation of individual nanotriangles in the reverse order when the linear polarization is rotated, whereas using a circular polarization, light−nanoparticle angular momentum transfer occurs via the generation of a Poynting vector vortex of reversed handedness. This work provides a new path for the control of light−matter angular momentum transfer using plasmonic nanogap antennas.

The near field was tailored to be enhanced at the three-phase boundary of Au-NPs/TiO2/H2O for efficient water oxidation.