Surface plasmon resonance (SPR), which is induced by the light irradiation of metal nanostructures, shows a number of potential applications in photonic or biosensing devices. Recently, the active tuning of SPR has received a good deal of interest. It is well known that SPR is strongly dependent on gap distances between nanostructures. Thus, we previously developed an active gap control system using volume changes in hydrogels. However, the real gap distances and their homogeneity during active tuning remain unclear. In this study, we evaluated gap distance changes between gold nanodots prepared on a polymer gel surface by nm-scale imaging and spectral analyses. A gold array with sub-100 nm dots was prepared on a silicon substrate and transferred onto a hydrogel surface. Active changes in the distances between the gold nanodots were confirmed by atomic force microscope (AFM) imaging and spectral measurement in an aqueous solution. Further, scanning electron microscope (SEM) imaging was successfully performed after exchange of the solvent in the polymer gels from water to a nonvolatile ionic liquid, providing clear images with a resolution of several nanometers in scale. SEM results supported the findings that active distance control using a polymer gel possesses high uniformity on a nanoscale. The optical properties of the gold nanodot arrays were calculated by an electromagnetic optical simulation based on the SEM images. The simulated spectra were in good agreement with the experimental spectra obtained on the hydrogel. These results provide strong support that the active control of nanostructures using a hydrogel possesses high controllability.
Superatoms, which can mimic the properties of elements different to the composed ones, have potential to be new building blocks. This time, we have developed the method of superatom synthesis in solution through typical metal assembly in a dendrimer template. In this study, we investigated fine-controlled assembly of typical metal units in the dendrimer. Metal assembly of the bismuth units enabled optical function using the dendrimer structure. In addition, controlled assembly of the aluminum units realized solution-phase synthesis of the superatom.
The strong electronic field generates under the excitation of plasmon resonance at the nanogap of Au bowtie structure with sub-micrometer scale. In this field, it is known that various unique optical phenomena, such as the selection rule breakdown or the formation of strong coupling states, can be induced. In our previous study, we have introduced the electrochemical potential control method into surface-enhanced Raman scattering (SERS) measurements to prove unique molecule catalysis depending on the molecule orientation. Through the measurements, we have succeeded in the observation of non-totally symmetric Raman mode excited by the charge transfer resonance at the specific electrochemical potential. On the other hand, several previous theoretical estimations predict that the optical force at the highly localized electric field shows the possibility for the single molecular trapping under the ambient condition due to its huge gradient force. In this study, we have tried to observe SERS from optically manipulated molecules at the plasmonic field in the room temperature solution. At the present experiment, we have performed in-situ electrochemical SERS measurements using a single bowtie structure. As the results, we have successfully observed the optical molecular condensation behavior at the nanogap of single Aubowtie structure depending on the incident light intensity or electrochemical potential.
The reaction of [PtAu24(SC2H4Ph)18]0 ([PtAu24]0) with an equimolar amount of NaBH4 selectively afforded oneelectron reduced cluster [PtAu24]– with seven valence electrons. Monitoring the reaction between an equimolar amount of [PtAu24]0 and [PtAu24]2– revealed that the stoichiometric formation of [PtAu24]– is ascribed to the spontaneous electron transfer (ET) from [PtAu24]2– to [PtAu24]0 remaining in the reaction solution. Theoretical calculation suggested that the larger adiabatic electron affinity of [PtAu24]0 compared to that of [PtAu24]– was the driving force of the spontaneous ET reaction even though the surface was fully passivated by thiolate ligands.