Tadashi Fukawa

Detection of Volatile Organic Compounds by Weight-Detectable Sensors coated with Metal-Organic Frameworks

Detection of volatile organic compounds (VOCs) using weight-detectable quartz microbalance and silicon-based microcantilever sensors coated with crystalline metal-organic framework (MOF) thin films is described in this paper. The thin films of two MOFs were grown from COOH-terminated self-assembled monolayers onto the gold electrodes of sensor platforms. The MOF layers worked as the effective concentrators of VOC gases, and the adsorption/desorption processes of the VOCs could be monitored by the frequency changes of weight-detectable sensors. Moreover, the MOF layers provided VOC sensing selectivity to the weight-detectable sensors through the size-selective adsorption of the VOCs within the regulated nanospace of the MOFs.

Site-Selective Electroless Nickel Plating on Patterned Thin Films of Macromolecular Metal Complexes

We demonstrate a simple route to depositing nickel layer patterns using photocross-linked polymer thin films containing palladium catalysts, which can be used as adhesive interlayers for fabrication of nickel patterns on glass and plastic substrates. Electroless nickel patterns can be obtained in three steps: (i) the pattern formation of partially quaterized poly(vinyl pyridine) by UV irradiation, (ii) the formation of macromolecular metal complex with palladium, and (iii) the nickel metallization using electroless plating bath. Metallization is site-selective and allows for a high resolution. And the resulting nickel layered structure shows good adhesion with glass and plastic substrates. The direct patterning of metallic layers onto insulating substrates indicates a great potential for fabricating micro/nano devices.

Macroporous conductive polymer films fabricated by electrospun nanofiber templates and their electromechanical properties

We demonstrate a facile method to fabricate macroporous poly (3,4-ethylenedioxythiophene)/poly (4-styrene sulfonate) (PEDOT/PSS) films with empty channels by using electrospun nanofiber as a sacrificial template. The channels within the PEDOT/PSS films were prepared by depositing PEDOT/PSS aqueous dispersion onto poly (vinyl pyrrolidone)/poly(methyl methacrylate) (PVP/PMMA) nanofiber template, and then the nanofibers were removed by solvent extraction. The average diameter of the channels is 313±45 nm, which is almost the same as the parent PVP/PMMA nanofibers. The macroporous PEDOT/PSS film with the empty channels showed an enhancement of electromechanical properties compared to the nonporous PEDOT/PSS film.

Volatile organic compound sensing by quartz crystal microbalances coated with nanostructured macromolecular metal complexes.

We report the construction of a molecular recognition layer composed of polyelectrolyte brushes and metal complexes on the surface of a quartz crystal microbalance (QCM) and the sensing abilities for various volatile organic compounds (VOCs). Atom-transfer radical polymerization of 2-(dimethylamino)ethyl acrylate from an initiator-terminated self-assembled monolayer yielded polyelectrolyte brushes on the surface of a weight-detectable quartz crystal microbalance. One end of a poly[(2-dimethylamino)ethyl methacrylate] brush was covalently attached onto the surface of a sensor. We found that metallophthalocyanines with four bulky pentaphenylbenzene substituents could adsorb volatile organic compounds selectively into their cavities. Macromolecular metal complexes were prepared by immersing polymer-brush-modified QCMs into an aqueous solution of sterically protected cobalt phthalocyanine. Anionic cobalt phthalocyanine was trapped in the polymer brushes and acted as a molecular receptor for the sensing of VOC molecules.

Novel MEMS oscillator using in-plane disk resonator with sensing platform and its mass sensing characteristics

We developed a new disk resonator which has high quality factor, highly efficient mass detection ability, and area-effective layout. High quality factor was achieved by minimizing support loss using nodal-point position control on the structural design. Sensing platform in the center hole provides wide and high-sensitive mass detection area. We also developed an oscillation circuit using impedance transform circuit which is suitable to MEMS resonators with high motional impedance. Toluene gas detection was demonstrated using this oscillator.

Rodlike macromolecules through spatial overlapping of thiophene dendrons.

Two novel dendritic macromonomers 7 and 8 functionalized with electroactive conjugated thiophene oligomers were synthesized by stepwise cross-coupling reactions and the introduction of a vinyl group at the focal point. Both macromonomers were polymerized into dendronized polymers 9 and 10 by using a radical polymerization method. The photophysical and redox behaviors of dendronized polymers 9 and 10 are significantly different from those of the corresponding macromonomers. This difference may result from the spatial overlapping of thiophene dendrons through π-π interactions when the dendrons are connected to a polymer backbone. The dendronized polymers can organize into large-area two-dimensional sheets with a thickness of 4.8 nm. Polymer 9, which has all-dendritic thiophene side chains, exhibited enhanced conductivity by partial doping with iodine or nitrosonium tetrafluoroborate (NOBF(4)). The novel amphiphilic dendronized polymer 15 was synthesized by the atom-transfer radical polymerization of macromonomer 7 from a poly(ethylene glycol) (PEG) macroinitiator and was found to have a self-organized structure in water.

High‐Sensitive Chemical Sensor System Employing a Higher‐mode Operative Micro Cantilever Sensor and an Adsorption Tube

We report the basic functions and the sensitivity improvement of a chemical sensor system employing a poly‐butadiene (PBD) coated micro cantilever sensor and a carbon‐fiber‐filled adsorption tube. The improvements of the sensitivity were carried out by two methods as 1) reduction of the volume in sensor camber by 1/30, 2) enlargement of the resonance frequency of the cantilever by 4.6 using a high speed analog‐oscillation circuits and a low noise package. Using the 4th vibration mode (resonant frequency 715 kHz) of a PBD coated cantilever (length 500 μm, width 100 μm, thickness 5 μm) and a small sensor chamber with a volume of 3.5 cc, the sensitivity was enhanced to be 2.4 Hz/ppm for toluene in nitrogen carrier gas with 10 minute adsorption time, which was about 100 times larger than our previous sensor system.

Solution-Processed Nanowire Coating for Light Management in Organic Solar Cells

We report a novel light management approach based on solution-processed nanowire (NW) coating for enhancing organic solar cell efficiency. A titanium dioxide (TiO2) NW dispersion was produced by electrospinning. The coatings with various coverage fractions were fabricated by a simple solution casting of a TiO2 NW dispersion. Reduced reflectivity was observed for the NW-coated glass slide. The bulk-heterojunction organic solar cells with the NW coating showed improved power conversion efficiencies (PCEs) due to their antireflection and light trapping effects in the active layer. In addition, the PCE of the cell with the NW coating was improved compared with that without the NW coating for incident angles above 70° (increased by a maximum of 51.6% at an incident angle of 85°). These results indicate that solution-processed NW coating is a promising light management approach easily scalable and applicable to a wide range of devices, including solar cells.