Hirobumi Ushijima

Metal-enhanced fluorescence platforms based on plasmonic ordered copper arrays: wavelength dependence of quenching and enhancement effects.

Ordered arrays of copper nanostructures were fabricated and modified with porphyrin molecules in order to evaluate fluorescence enhancement due to the localized surface plasmon resonance. The nanostructures were prepared by thermally depositing copper on the upper hemispheres of two-dimensional silica colloidal crystals. The wavelength at which the surface plasmon resonance of the nanostructures was generated was tuned to a longer wavelength than the interband transition region of copper (>590 nm) by controlling the diameter of the underlying silica particles. Immobilization of porphyrin monolayers onto the nanostructures was achieved via self-assembly of 16-mercaptohexadecanoic acid, which also suppressed the oxidation of the copper surface. The maximum fluorescence enhancement of porphyrin by a factor of 89.2 was achieved as compared with that on a planar Cu plate (CuP) due to the generation of the surface plasmon resonance. Furthermore, it was found that while the fluorescence from the porphyrin was quenched within the interband transition region, it was efficiently enhanced at longer wavelengths. It was demonstrated that the enhancement induced by the proximity of the fluorophore to the nanostructures was enough to overcome the highly efficient quenching effects of the metal. From these results, it is speculated that the surface plasmon resonance of copper has tremendous potential for practical use as high functional plasmonic sensor and devices.

Detection of Adrenaline on Poly(3-aminobenzylamine) Ultrathin Film by Electrochemical-Surface Plasmon Resonance Spectroscopy

In this Article, we present a novel method to detect adrenaline on poly(3-aminobenzylamine) (PABA) ultrathin films by electrochemical-surface plasmon resonance (EC-SPR) spectroscopy. We prepared a PABA film, which specifically reacts with adrenaline, on a gold electrode by electropolymerization of 3-aminobenzylamine. The specific reaction of benzylamine within the PABA structure with adrenaline was studied by XPS, UV-vis spectroscopy, and EC-SPR techniques. Adrenaline was detected in real time by EC-SPR spectroscopy, which provides simultaneous monitoring of both optical SPR reflectivity and electrochemical current responses upon injecting adrenaline into the PABA thin film. The number of changes in both current and SPR reflectivity on the injection of adrenaline exhibited the linear relation to the concentration, and the detection limit was 100 pM. The responses were distinctive to those for uric acid and ascorbic acid, which are major interferences of adrenaline.

Overlay of semi-dried functional layers in offset printing for rapid and high-precision fabrication of flexible TFTs

We achieved a reduction in the misregistration of overlying patterns printed on a flexible plastic film and a drastically shorter processing time with fully printed thin-film transistor (TFT) fabrication. This was achieved using a newly developed wet-on-wet (WoW) printing process wherein a subsequent layer can be printed on a previous semi-dried (not-sintered) layer. In the WoW process, as examined by rheological measurements, a semi-dried (highly solidified) state of ink was attained before transferring by utilizing the solvent uptake of a PDMS blanket in offset printing to ensure the structural integrity of the ink layer, and to reduce the inter-contamination of adjoining layers. Loss-on-drying tests and resistivity measurements indicated that molecular penetration at the boundary of adjoining layers with a length of c.a. 70 nm occurred in the WoW process; however, with thicker electrodes, we successfully fabricated a WoW-processed TFT whose performance was comparable with a TFT formed by a conventional printing process.

Hydrophobic attraction between silanated silica surfaces in the absence of bridging bubbles.

The interaction forces between silanated silica surfaces on which there were neither nanobubbles nor a gas phase were measured using colloidal probe atomic force microscopy (AFM). To obtain hydrophobic surfaces without attached nanobubbles, an aqueous solution was introduced between the surfaces after an exchange process involving several solvents. In the approaching force curves obtained, an attractive force was observed from a distance of 10-25 nm, indicating the existence of an additional attractive force stronger than the van der Waals attraction. In the retracting force curves, a strong adhesion force was observed, and the value of this force was comparable to that of the capillary bridging force. The data clearly showed that although the bridging of nanobubbles is responsible for long-range hydrophobic attraction, there also exists an additional attractive force larger than the van der Waals attraction between hydrophobic surfaces without nanobubbles. Both the ionic strength and the temperature of the solution had little influence on the force. The possible origin of the force is discussed on the basis of the obtained results.

Effect of pyrolysis temperature on the magnetic properties of the carbon materials prepared from trialkylboranes

Magnetic properties of amorphous carbon materials, prepared by pyrolysis of trialkylboranes, were examined using the superconducting quantum interference device and the electron spin resonance (ESR) methods. It is found that the observed magnetic properties could be greatly affected by pyrolysis temperature and the analysis of the magnetization curves observed in the magnetic field range 0–1 T has shown that these samples are basically of a superparamagnetic character. The ESR measurements have also supported these aspects.

Analysis of Adsorption and Binding Behaviors of Silver Nanoparticles onto a Pyridyl-Terminated Surface Using XPS and AFM

In this study, we analyzed adsorption and binding behaviors of citrate-capped silver nanoparticles (AgNPs) on a pyridyl-terminated surface using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Adsorption of the AgNPs onto the pyridyl-terminated silicon wafer surface was completed through pH-controlled sol immersion. The adsorption occurred predominantly at a pH less than the pK(b) value of the pyridyl group and more than the pK(a1) of citric acid, indicating that the driving force behind adsorption was electrostatic interaction. Adsorption of citrate onto the pyridyl group also occurred at pK(a1) < pH < pK(b) without AgNPs. According to XPS in the N1s region, larger deprotonation from the pyridinium-formed pyridyl groups was demonstrated subsequent to adsorption of the AgNPs. The deprotonation from the pyridinium indicates the formation of the neutral pyridyl group as the counterpart of hydrogen bonding with the carboxyl group of citrate. The binding state between the pyridyl group and citrate surrounding AgNPs is expected to be kept stable through hydrogen bonding and van der Waals force derived from the AgNPs approach to the pyridyl surface.

A stable carbon-based organic magnet

The amorphous-like carbon compound prepared by direct pyrolysis of 1,2-diaminopropane is found to be a stable strong magnet, the apparent saturation magnetization (Ms) of which is 10.5 emu g–1(0.022 µB per carbon atom), being comparable to ca. one-third of magnetite (Fe3O4, 30.7 emu g–1).

Micro/nanopatterning of single-walled carbon nanotube–organic semiconductor composites

In this study, micro/nanopatterning and assembly of single-walled carbon nanotube-organic semiconductor composites using dip-pen nanolithography, microcontact printing and fountain-pen nanolithography techniques are described. First, the solubilization abilities of carbon nanotubes with Alcian blue-tetrakis(methyl pyridium) chloride (AB) are investigated by UV-visible spectroscopy. The assembly of the composites obtained by microcontact printing technique shows well-ordered monolayers of 1 microm linewidth pattern. Dip-pen nanolithography shows that 11 nm height and 100 nm linewidth can be obtained on silicon wafer substrates. Finally, fountain-pen nanolithography is shown as a possible large-scale carbon nanotube assembly technique.

Fabrication of embedded electrodes by reverse offset printing

We developed a novel offset-printing process that permits the fabrication of silver-nanoparticle electrodes embedded in a dielectric layer. We succeeded in embedding approximately 1 µm thick silver electrodes to a dielectric layer with thickness ratio of 1:1.4. The surface-height difference between the embedded electrode and the surrounded dielectric layer was less than 80 nm. By virtue of the surface uniformity of this embedding process, the interconnect breakage of orthogonal wires printed on top of the underlying wire was drastically reduced to 4%, compared to 41% for non-embedded wires. The electric conductivity of embedded electrodes with thickness ≈110 nm was about 10 µΩ cm−1, which was comparable to that of a silver pattern formed on a glass substrate alone. We also examined the characteristics of fully printed thin-film transistors composed of the embedded electrodes, and measured an average mobility of 0.07 cm2 V−1s−1. These results demonstrate the applicability of the proposed technique to the fabrication of printed circuits and devices including active elements.

Continuous fine pattern formation by screen-offset printing using a silicone blanket

Screen-offset printing combines screen-printing on a silicone blanket with transference of the print from the blanket to a substrate. The blanket absorbs organic solvents in the ink, and therefore, the ink does not disperse through the material. This prevents blurring and allows fine patterns with widths of a few tens of micrometres to be produced. However, continuous printing deteriorates the patterns shape, which may be a result of decay in the absorption abilities of the blanket. Thus, we have developed a new technique for refreshing the blanket by substituting high-boiling-point solvents present on the blanket surface with low-boiling-point solvents. We analyse the efficacy of this technique, and demonstrate continuous fine pattern formation for 100 screen-offset printing processes.