The excitation of the localized surface plasmon leads to the generation of highly localized electric field. Within the
field, the huge field gradient can manipulate molecular behavior, resulting in possible modulation of chemical reactions at
electrified interfaces with plasmon-active metal nanostructures. In this study, we have observed the effect of the
plasmonic excitation on the plasmon-induced hydrogen evolution reactions. Through various photoelectrochemical
measurements, the appearance of the unique molecular process has been observed through the examination of the isotopic
effect. In addition, the functionalization of the plasmonic electrode using the molecular catalyst has also been examined.
The gradient force in the electric field induced by the localized surface plasmon resonance (LSPR) could retard the
molecular Brownian motion at solid-liquid interface. Up to date, we have already demonstrated the molecular selective
manipulation through surface-enhanced Raman scattering (SERS) measurements. However, several effects, such as the
solvents, solvation, molecular interaction, and ion pair formation, on molecular manipulation are still unclear. In this
study, we have tried to reveal the crucial factors for the efficient control of the molecular manipulation within the LSPR
induced electric field through SERS observations using Au array structure.
It has been expected that the gradient force in the electric field induced by the excitation of the localized surface plasmon resonance (LSPR) could retard the molecular Brownian motion, if molecules has enough polarizability to generate optical force beyond thermal fluctuation. In this study, we have attempted to observe the optical molecular manipulation at the gap of plasmonic bow-tie nanostructures in the bi-analyte solution of molecules. Through the evaluation of the surface diffusion process by electrochemical surface-enhanced Raman scattering (SERS) measurements, it has been found that the control of the electrochemical potential of the metal nanostructures realized the molecular selective manipulation. In addition, we have successfully observed the formation of unique phase of molecule condensation at electrified interface.
Highly localized electric field induced by the excitation of the localized surface plasmon provides huge gradient of the field intensity in nano-scale. Such gradient results in exotic perturbation for molecules at electrified interfaces with plasmonically-active metal nanostructures. In this study, plasmon-induced hydrogen evolution reactions have been successfully induced by the combination of the plasmonic metal nanostructures on the p-type GaP semiconductor electrode. Through various photoelectrochemical measurements, it was found that the present system showed the relatively higher efficiency under the neutral condition compared with the acidic and the basic conditions. In addition, the unique molecular process has been observed by using the isotopic water molecules. By the examination of the isotopic effect, the effect of the field localization on the reaction was discussed.
Optical manipulation has been used for the trapping of micrometer-scaled objects, but it is still difficult to control the motion of small molecules on the nanometer scale at room temperature. Plasmonic metal nanostructures are expected to be useful for the optical manipulation of nanoscale molecules using a highly localized electric field. We use the plasmonic Ag nanostructure for a demonstration of optical trapping through the observation using surface-enhanced Raman scattering (SERS) imaging. The optical measurements were conducted under electrochemical potential control to stabilize the nanostructure with target molecules, 4,4′-bipyridyl (44 bpy). Upon increasing the concentration of 44 bpy molecules in an electrolyte solution at room temperature, the blinking frequency of the SERS signal was different in both the spectra and imaging. The dwell time of the SERS signals was increased from several tens of milliseconds to a few seconds, which suggested the successful observation of plasmonic trapping of small molecules through the surface diffusion control. The observed results prove the importance for the control of the surface coverage of the molecules and its influence on surface diffusion under plasmonic molecular trapping.
It is predicted by various theoretical studies that nanometer size molecules could be trapped in the strong electromagnetic field due to its steep spatial gradient of the filed intensity. In this study, we have attempted to observe the plasmonic molecular trapping behavior in the mixed solution of 4,4’-bipyridine and 2,2’-bipyridine by surface enhanced Raman scattering measurements. In order to control the molecular optical trapping selectivity, we have introduced the electrochemical potential control into the system. The experimental results would indicate the achievement of the selective control of molecular optical trapping at room temperature in solution.
We have attempted to control molecular behavior of a small number of molecules which are strongly coupled with the localized light energy in the vicinity of the metal nano structures. The new hybridized state derived from the formation of the strong coupling state shows unique optical properties, so the active control of this has been attracting researches in various fields. At the present attempts, we have achieved controlling the LSP energy and the coupling strength of the coupling via electrochemical method. The electronic and vibrational states of organic dye molecules in strongly coupled with LSP has been investigated through electrochemical in-situ surface-enhanced Raman scattering (SERS) measurements, providing the vibrational and the electronic structure of molecule in the coupling state.
The optical property of plasmon-active metal nano dimer structure strongly depends on its shape and gap distance. Thus, the precise control of metal nano structure has been receiving much attention in various field. In the present study, we have tried to control the plasmonic property by combining electrochemical method with in-situ dark-field microscopy. Controlled metal dissolution in the size range below a few nm leads to the successful switching from the charge transfer plasmon (CTP) to the bonding dipolar plasmon (BDP) mode. The highly localized plasmonic field generated during the switching could be applied for various applications including molecular optical trapping in solution at room temperature.
Plasmon-induced photo-polymerization of the conductive polymer was performed on the Au-TiO2 composite photo electrode. Thorough the examination of the spatial distribution of the conductive polymer which was deposited in the vicinity of metal nano-structures, the visualization of the spatially localized strong optical field have been achieved. Not only for the visualization of the generated strong optical field but also the determination of the absolute electrochemical potential for the generated hole for the oxidation of the monomer molecules. Using the present technique, the higher order resonances at the Au nanorod structures are also examined to generate highly-selective polymer deposition.
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