We tuned the plasmonic properties of the Au lattice structure by electrochemical potential control. Au lattice structures with different values of the spacing, diameter, and height show characteristic optical properties determined by the surface lattice resonance of the localized surface plasmon mode. Electrochemical potential control can change the metal structures through metal dissolution, as well as the energy of the electrons in metals. In situ real time observation of the optical properties of Au lattice structures by electrochemical dark-field scattering microscopy shows the fine-tuning of the plasmonic properties with characteristic resonance energy and controlled spectral width. By controlling surface dissolution of the Au lattice structure at a rate of a few nanometers per minute, we tuned the plasmonic properties and achieved a spectral width of 0.145 eV at a maximum resonance of 1.74 eV (714 nm).

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Herein, we report the control of the optical properties of metal nanodimer structures using electrochemical metal dissolution reactions. The reaction rate could be precisely tuned by changing the electrochemical potential and, as a consequence, fine tuning of the size and gap distance of metal nanodimers was achieved as the functions of applied potential and polarization time. The observed linear correlation between the scattering intensity and charge resulting from nanostructure dissolutions suggested that the surface dissolution rate was 0.30 nm min, corresponding to the surface dissolution of a single atomic layer per min. The present method can control the change in the volume of the structures, leading to the change in the gap distance of nanodimers at an atomic-scale level.

Efficient use of light energy is regarded as a key factor in solving energy challenges to create a sustainable society. The highly concentrated photon energy generated by localized surface plasmon resonance excitation in the vicinity of metal nanostructures can enhance light‐matter interaction. Optimization of the interactions between plasmons and electrons in materials can lead to novel light energy applications. To overcome the current limitations for these interactions, the plasmon field must be focused to an extremely small size close to the molecular scale. Formation of the plasmonic field at the quantum limit may cause interesting phenomena with unique photoresponses. Recently, following the development of nanofabrication techniques, detailed investigations have been undertaken to understand these processes. In this focus review, we describe recent advances in the strong interactions between highly localized photons and electrons in nanomaterials, including molecules, nanocarbons, and quantized nanoparticles. First, we outline the plasmonic properties that depend on the metal nanostructures. In addition, we describe surface‐enhanced Raman scattering (SERS), which is used to detect interactions between plasmons and materials. The importance of the resonant electronic excitation process, which is a chemical effect based on the charge transfer contribution, is discussed while considering the unique molecular selectivity in SERS. We then highlight the unique photoresponse properties that are used for ultra‐sensitive detection of single molecules by the localized plasmon field. These properties are major advantages of the plasmon field. Next, we introduce strong coupling between plasmons and excitons. This coupling state is promising because of its ability to modify the intrinsic optical properties of materials via creation of a novel absorption wavelength region to accumulate the light energy. Finally, we discuss the use of plasmon excitation for effective chemical reactions accompanied by electron transfer. We conclude that reduction of light to the molecular scale would open novel routes for energy manipulation required by the next generation.

Electrogenerated chemiluminescence (ECL) microscopy shows promise as a technique for mapping chemical reactions on single nanoparticles. The technique’s spatial resolution is limited by the quantum yield of the emission and the diffusive nature of the ECL process. To improve signal intensity, ECL dyes have been coupled with plasmonic nanoparticles, which act as nanoantennas. Here, we characterize the optical properties of hexagonal arrays of gold nanodisks and how they impact the enhancement of ECL from the coreaction of tris­(2,2′-bipyridyl)­dichlororuthenium­(II) hexahydrate and tripropylamine. We find that varying the lattice spacing results in a 23-fold enhancement of ECL intensity because of increased dye-array near-field coupling as modeled using finite element method simulations.