Reactivity of hydroxy- and aquo(hydroxy)-λ3-iodane-crown ether complexes.

We have designed a series of hydroxy(aryl)-λ(3)-iodane-[18]crown-6 complexes, prepared from the corresponding iodosylbenzene derivatives and superacids in the presence of [18]crown-6, and have investigated their reactivities in aqueous media. These activated iodosylbenzene monomers are all non-hygroscopic shelf-storable reagents, but they maintain high oxidizing ability in water. The complexes are effective for the oxidation of phenols, sulfides, olefins, silyl enol ethers, and alkyl(trifluoro)borates under mild conditions.

Enhancement of a Two-Photon-Induced Reaction in Solution Using Light-Harvesting Gold Nanodimer Structures.

We performed a quantitative analysis of plasmon-assisted two-photon photochromic reactions on light-harvesting gold nanodimer structures. Our strategy for the quantitative analysis of two-photon-induced photochemical reactions on gold nanostructures is using not only a confined photochemical reaction chamber but also a solution system. The strong intensification of near-field light at the nanogap positions on gold nanodimer pairs promoted two-photon absorption by a closed-form diarylethene derivative, resulting in highly efficient photochromic conversion to the open-form structure.

Spectral properties of nanoengineered Ag/Au bilayer rods fabricated by electron beam lithography.

Ag/Au bimetallic nanoparticles possess the combinatory advantages of Au and Ag nanoparticles and can also be utilized to tune the properties of localized surface plasmon resonance. Ag/Au bilayer nanorods were prepared by electron beam lithography, and their spectral properties were investigated. Compared with Ag monolayer nanorods, Ag/Au bilayer nanorods show broader localized surface plasmon resonance bands, and the longitudinal mode and transverse mode localized surface plasmon bands show blueshift and redshift, respectively.

Spectral properties and mechanism of instability of nanoengineered silver blocks.

The instability of silver nanoblocks under atmospheric conditions is investigated. The localized surface plasmon resonance band of the silver nanoblocks shows a red shift, broadening, and damping with increasing storage time under atmospheric conditions. The change in spectral properties of silver nanoblocks is considered to be due to sulfidation of silver and structural breakage of silver nanoblock based on scanning electron microscope observation and numerical simulation.

Direct imaging of nanogap-mode plasmon-resonant fields.

We perform direct local-field imaging of a plasmon-resonant gold nanoparticle pair separated by a gap of several nanometers using a scattering-type near-field optical microscope with a sharp silicon tip of atomic force microscope. The sharp tip allows the access for the nanogap and the high spatial resolution. Our results provide experimental evidence that the nanogap structure produces an optical spot with the size of a single nanometer (<10 nm).

Essential nanogap effects on surface-enhanced Raman scattering signals from closely spaced gold nanoparticles.

We have demonstrated the essential nanogap effects on surface-enhanced Raman scattering (SERS) signals obtained from two diagonally aligned gold nanoparticles with several nanometre separations, which were precisely fabricated on a glass substrate. This is the first proof of principle for extracting the light localization effects on SERS due to the formation of nanogaps from experimentally observed SERS signals.

Highly controlled surface-enhanced Raman scattering chips using nanoengineered gold blocks.

Well defined gold nanostructures of various sizes are fabricated on glass substrates using high-resolution electron-beam lithography/lift-off techniques and detailed surface-enhanced Raman scattering (SERS) properties of crystal violet molecules are studied in order to elucidate electromagnetic (EM) field enhancement effects on the fabricated structures. SERS measurements are performed with high reproducibility using in situ Raman microspectroscopy in aqueous solution. An analysis based on EM theory is performed using field-enhancement factors obtained from finite-difference time-domain (FDTD) simulations and the analysis reproduces experimental results very well.

Development of interdigitated array electrodes with surface-enhanced Raman scattering functionality.

Interdigitated array electrodes with surface-enhanced Raman scattering (SERS) functionality for in situ qualitative and quantitative analysis of electroactive species are demonstrated. Gold nanostructured interdigitated array electrodes (NIDAEs) were fabricated by electron beam lithography, and used for an electrochemical SERS study of K(3)[Fe(CN(6))] in aqueous KClO(4) solution in single and generation-collection modes. The generation-collection mode experiment showed amplification of the SERS band intensity for adsorbed ferricyanide ions at the negative end of the applied potential, while in single mode it was reduced to near zero.

Nanoparticle plasmon-assisted two-photon polymerization induced by incoherent excitation source.

We demonstrate the possibility to achieve optical triggering of photochemical reactions via two-photon absorption using incoherent light sources. This is accomplished by the use of arrays of gold nanoparticles, specially tailored with high precision to obtain high near-field intensity enhancement.