Tunneling spectroscopy of isolated gold clusters grown on thiol/dithiol mixed self-assembled monolayers

We report a scanning tunneling spectroscopy study on the size-tunable isolated gold nanoclusters grown on thiol/dithiol mixed self-assembled monolayers (SAMs) where the effect of neighboring clusters are practically excluded. The structure forms double tunnel junction system in which the spectra exhibit Coulomb staircases. With increasing cluster size the standard deviation of the offset charge distribution for clusters increases, accompanied with the increase of total capacitance. The results are qualitatively same with the previous ones where clusters are densely grown on the substrate, indicating that this behavior is an intrinsic property for the double tunnel junction structures of tip/vacuum/single cluster/SAMs/Au(1 1 1) systems.     

Enhancement of resolution and quality of nano-hole structure on GaN substrates using the second-harmonic beam of near-infrared femtosecond laser

By using a second harmonic of near infrared femtosecond (fs) laser (λ=387 nm, 150 fs) with high NA objective lens, fabrication resolution has been greatly improved in nano-fabrication of wide band-gap semiconductor gallium nitride (GaN). We have carried out a wet-chemical-assisted fs laser ablation method, in which the laser beam is focused onto a single-crystal GaN substrate immersed in a concentrated hydrochloric (HCl) acid solution. A two-step processing involving irradiation with a fs laser beam in air followed by wet chemical treatment is also performed for comparison. In the wet-chemical-assisted ablation, theoretical diameters of ablation craters are calculated as a function of pulse energy by assuming that the reaction is based on two-photon absorption. In lower energy, the calculated curve is close to the experimental value, while the actual measured diameters in the region of higher energy are larger than calculated values. In the condition of the highest fabrication resolution, we obtained ablation craters smaller than 200 nm at full width at half maximum. We have also demonstrated the fabrication of two-dimensional (2D) periodic nanostructures on surface of a GaN substrate using the second harmonic single fs-laser pulse. Uniform ablation craters with the size as small as 410 nm in diameter are arranged with a periodicity of 1 μm. Such structures are applicable to 2D photonic crystals which improve the light extraction efficiency for blue LEDs in the near future.     

Rapid fabrication of optical volume gratings in Foturan glass by femtosecond laser micromachining

We report on rapid fabrication of optical volume gratings in Foturan glass using a modulated femtosecond laser focused with cylindrical lenses. An optical volume grating with an area of 2 mm ×3 mm and ∼2 mm thickness can be achieved within 10 min by use of this method. Optical micrography confirms the volume nature of the gratings and shows that they consist of 10 μm-thickness planes with a period of 15 μm. The diffraction efficiency is examined to be ∼56%. The limitations and future implementations of the fabricated volume gratings are discussed.     

Reactions of highly branched fluoroolefins with methyllithium and methylmagnesium bromide: formations of unexpected polyfluorocyclobutene and polyfluoropentadiene compounds

Introduction of a methyl group into hexafluoropropene trimers was achieved by reactions with organometallic carbon nucleophiles. Unusual cyclization and defluorination occurred simultaneously with a formation of methylated polyfluoroolefins: excess methyllithium provided a polyfluorocyclobutene compound, while a polyfluoropentadiene derivative was formed by use of excess methyllithium.     

Functional monomers and polymers. XCV. Photochemical reactions on synthetic polymers having pendant thymine bases in polymethyl methacrylate film

The photodimerization reaction of synthetic polymers which contain thymine bases was studied in polymethyl methacrylate film. The quantum efficiency for the photodimerization of the thymine bases of polyacrylate and polymethacrylate, fixed in the polymethyl methacrylate film was measured. The value of the film was higher than those measured in solution.     

Cyclotron resonance of polarons in AgBr at high microwave fields

A cyclotron resonance experiment on polarons in pure AgBr has been extended to the microwave field of 3 kV cm^?1 by using a pulsed magnetron at 35 GHz at lattice temperatures of 4.2 and 17 K in magnetic fields up to 58 kOe. It was established that the ground state polaron mass is m¹_p(0)=(0.287±0.003)m_e. From microwave field dependences of the peak position and the width of resonance lines, it was established that the electron polaron follows the streaming motion repetitively emitting LO-phonons in the microwave field region above 80 V cm^?1. Further, it was also suggested that, when streaming, the polaron has an enhanced effective mass of (0.353±0.006)m_e rather than the ground state mass m¹_p(0).     

Radical-initiated copolymerization of carbon monoxide and ethylenimine in the presence of ethylene

The radical-initiated copolymerization of carbon monoxide and ethylenimine in the presence of ethylene was studied quantitatively. Carbon monoxide copolymerized with difficulty with ethylenimine with α,α′-azobisisobutyronitrile as radical initiator. In the presence of a small amount of ethylene, however, a remarkable amount of crystalline powdery poly-β-alanine (nylon 3) was obtained. The crystalline copolymer, which mainly consists of nylon 3 and contains a small amount of nylon 5 and other substances of higher homologous nylon structure, was obtained in the presence of a large amount of ethylene. This copolymer scarcely contained any ketone structure. Increasing the total feed of the equimolar mixture of the monomers increased the conversion of total monomer and nylon 3 content in the copolymer formed. The effect of increasing carbon monoxide content in this system was to increase both the conversion and the nylon 3 content in the copolymer. In both cases the copolymers were almost identical with nylon 3. Increased ethylene content in the monomer feed, however, increased the conversion and the content of higher homologous nylon structures, such as nylon 5 and 7. From the results it was concluded that ethylene was involved not only in the propagation reaction but also particularly in the initiation reaction.     

Selective cell culture on UV transparent polymer by F2 laser surface modification

A microchip made of UV transparent polymer (CYTOP) that can perform selective cell culture has been fabricated by F₂ laser surface modification. The refractive index of CYTOP is almost the same as that of culture medium, which is essential for three-dimensional (3D) observation of cells. The F₂ laser modification of CYTOP achieves hydrophilicity only on the laser irradiated area with little deterioration of the optical properties and surface smoothness. After the laser modification, HeLa cells were successfully cultured and strongly adhered only on the modified area of CYTOP. The cells patterned on CYTOP were applied for clear 3D observation using an optical microscope in phase contrast mode.     

Three‐dimensional femtosecond laser micromachining of photosensitive glass for biomicrochips

Internal modification of transparent materials such as glass can be carried out using multiphoton absorption induced by a femtosecond (fs) laser. The fs‐laser modification followed by thermal treatment and successive chemical wet etching in a hydrofluoric (HF) acid solution forms three‐dimensional (3D) hollow microstructures embedded in photosensitive glass. This technique is a powerful method for directly fabricating 3D microfluidic structures inside a photosensitive glass microchip. We used fabricated microchips, referred to as a nanoaquarium, for dynamic observations of living microorganisms. In addition, the present technique can also be used to form microoptical components such as micromirrors and microlenses inside the photosensitive glass, since the fabricated structures have optically flat surfaces. The integration of microfluidics and microoptical components in a single glass chip yields biophotonic microchips, in other words, optofluidics, which provide high sensitivity in absorption and fluorescence measurements of small volumes of liquid samples.