Nanoscale Helical Optical Force for Determining Crystal Chirality.

The deterministic control of material chirality has been a sought-after goal. As light possesses intrinsic chirality, light-matter interactions offer promising avenues for achieving non-contact, enantioselective optical induction, assembly, or sorting of chiral entities. However, experimental validations are confined to the microscale due to the limited strength of asymmetrical interactions within sub-diffraction limit ranges. In this study, a novel approach is presented to facilitate chirality modulation through chiral crystallization using a helical optical force field originating from localized nanogap surface plasmon resonance. The force field emerges near a gold trimer nanogap and is propelled by linear and angular momentum transfer from the incident light to the resonant nanogap plasmon. By employing Gaussian and Laguerre-Gaussian incident laser beams, notable enantioselectivity is achieved through low-power plasmon-induced chiral crystallization of an organic compound-ethylenediamine sulfate. The findings provide new insights into chirality transmission orchestrated by the exchange of linear and angular momentum between light and nanomaterials.

Quantum-Coherence-Enhanced Hot-Electron Injection under Modal Strong Coupling.

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.

Spin-Orbit Angular-Momentum Transfer from a Nanogap Surface Plasmon to a Trapped Nanodiamond.

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.

Near-field engineering for boosting the photoelectrochemical activity to a modal strong coupling structure.

Near-field engineering is considered a significant strategy in constructing plasmonic nanostructures for efficient plasmonic chemistry. We demonstrate interfacial near-field engineering on a Au-NP/TiO2/Au-film (ATA) photoanode to improve the water oxidation efficiency. To tailor the near-field distribution, postdeposited Au on an ATA electrode (Au@ATA) is implemented using a facile constant potential electrolysis technique. As a result, the average photocurrent conversion efficiency of Au@ATA is approximately 1.3-fold higher than that of ATA.