Construction of nanomaterials has been developed from both top-down and bottom-up approaches. In these approaches, surfactant-templated mesoporous materials are promising because of their tunability, uniformity and reproducibility in both the size and shape of produced mesopores. Mesoporous silica materials have been widely and deeply investigated in the early stage, basing on the sol-gel chemistry of silicate. Although insulating mesoporous silica cannot be directly applicable to electrode materials, the mesoporous silica films and their hybrid films are recently applied as hard templates and electrodeposition of metals inside the mesopores realizes the formation of metal nanowire assembly, which has parallel orientation to the electrode surface. Furthermore, the mesoporous silica film with perpendicularly oriented mesochannels are prepared and used as hard-template, resulting in the fabrication of metal nanowire assembly standing on the electrode surface. On the other hand, conductive materials are recently fabricated as mesoporous structure by the surfactant-template method. Mesoporous carbon becomes the most conventional mesoporous conductive material and has been investigated as the electrode material mainly applicable to energy conversion. By introducing catalyst particles and ionomers inside mesochannels, triple phase boundary can be constructed and the application toward cathode electrode in the polymer electrolyte fuel cell (PEFC) has been investigated.
An electroactive polymer, poly[9,9-bis(p-isopropylphenylsulfanyl)fluorene-alt-N-decylcarbazole] (P2) was prepared. Electrochemical fluorodesulfurization was carried out using a P2-coated platinum anode. From 1H-NMR, EDX analyses, about 50% fluorodesulfurization at the 9-position of fluorene was confirmed. The UV-vis absorption spectra of the novel donor-acceptor copolymer containing n-type unit exhibited intramolecular charge transfer (ICT) character.
A new method for mask-less fabrication of metal micro-rods is described. The developed solution flow type droplet cell micro fabrication technique was applied to form Cu micro-rods. The use of an inner capillary tube as a mold during electrodeposition, makes it possible to form Cu micro-rods of about 15 mm length and about 100 µm diameter. The length is controlled by the deposition time. From X-ray analysis and surface observations, the formed Cu micro-rod is polycrystalline and the crystals are very fine. The cross section of the micro-rod was almost circular and the diameter was almost the same throughout its length. This technique also makes it possible to form straight metal structures as well as branched and layered micro-rods. This layered micro-rod fabrication technique can be applied to form resistance controlled micro wires.
Microcontact printing (μCP) with various proteins has been widely applied to biosensors and cell biology research. However, the mechanism of protein patterning in the μCP process is not clear in detail. We have electrochemically estimated enzyme concentration on glass slide patterned with μCP technique. We also estimated the enzyme concentration at the surface of poly(dimethylsiloxane) (PDMS), which corresponded to the enzyme activity at the PDMS stamp just before μCP. Our result suggested that it was possible to transfer enzyme monolayer from PDMS to glass surfaces with 100% efficiency with μCP. Immunoglobulin G (IgG) patterned with μCP was also characterized by tagging with enzyme labeled anti-IgG. Scanning electrochemical microscopy (SECM) image was obtained to visualize line and space pattern of IgG monolayer.
A novel solid electrolyte type ammonia (NH3) gas sensor was fabricated by the combination of the trivalent aluminum cation conducting solid electrolyte (Al0.2Zr0.8)20/19Nb(PO4)3 with La2O2SO4–(NH4)2HPO4 as an auxiliary sensing electrode. Since the present sensor exhibited such a superior sensing performance of theoretical response, which obeys the Nernst relationship between the sensor EMF output and the logarithm of the NH3 gas concentration along with the stable, continuous, and reproducible response even under humidified condition, it is greatly expected to be applied to a practical NH3 gas sensing device.
A new amperometric sensor based on proton conducting membranes to CO was investigated. It was observed that the sensor current density showed almost linearity against CO concentration in the range of 0–3000 ppm at 200°C. In addition, the sensitivity at less than 300 ppm CO was detected clearly using phosphoric acid doped polybenzimidazole (PBI) membrane. It was found that PBI membrane had high selectivity of CO to H2 in combustor exhaust gases at 200°C. Sensor performance using PBI membrane was less influenced by humidity than Nafion.
Cubic-shaped Pt nanoparticles have been deposited on carbon fiber (CF) electrode surfaces directly by two electrochemical techniques, namely, potential cycling and stepping in an aqueous solution of 1 mM K2PtCl4 and 0.1 M H2SO4 containing 1 mM NaI. It is shown that both nucleation and growth processes of the Pt phase formation on the CF surfaces were extensively suppressed by the strong interaction between Pt surface and I− anions. Consequently, this has lead to the formation of the highly dispersed preferentially cubic-shaped Pt nanoparticles.
A single crystal and polycrystals of GaN grown by the Na-flux method were photoelectrochemically characterized. The flatband potential of the GaN single crystal was approximately 0.2 V anodic of the potential of the GaN layer grown by metal-organic vapor phase epitaxy. Clear photo-electrochemical response was observed for the GaN single crystal. The turn-on slopes of the photocurrent for the poly-crystalline samples were gentler than the slope for the single crystal. The turn-on slopes were probably affected by the high resistivity of grain boundaries in the polycrystalline samples.
It is important to reveal the growth mechanism of the conductive polymer upon electrochemical polymerization in order to control the morphology of the film as a shape of the conductive polymer. In this paper, the relation between the structure of the polypyrrole as the conductive polymer and the quantity of electricity during galvanostatic polymerization was studied with the microscopic observation. With the quantity of electricity in the current density of 0.75 to 7.5 A·m−2, a particle of polypyrrole grew up to 15 µm in size at maximum while the thickness of the polypyrrole film was increased accompanying a stagnant behaviour around 25 µm to some extent, indicating increase in packing density of the polypyrrole particles.
Fabricating reference field effect transistor (FET) sensors instead of reference electrodes are important for the miniaturization and variegated applications of FET sensors. To make a reference FET, the gate surface of FET was modified with the self-assembled monolayer (SAM) of n-octadecyltrimethoxysilane (ODS). Though an ODS-SAM FET had low pH-sensitivity, it was cation-sensitive. This work demonstrates the relation between the surface morphology and the cationic and pH-sensitivity of ODS-SAM FETs. A roughness parameter of atomic force microscope images, the mean summit curvature (Ssc) has correlation with the cationic and pH-sensitivity of ODS-SAM FETs.
Poly(vinylidene fluoride) (PVDF) membranes with conical and cylindrical nanopores were prepared in a controlled manner by the ion-track technique, which involved heavy-ion beam irradiation and subsequent alkaline etching. The etching behavior mainly depended on the energy deposition of the ion beams, and thus its depth distribution, estimated by theoretical simulation, was successfully applied to control the shapes and diameters of the etched pores. Scanning electron microscopy (SEM) and electrolytic conductometry provided an insight into the critical experimental parameters. Interestingly, applying a higher voltage to the conductometry cell promoted track etching up to breakthrough probably because electrophoretic migration of the dissolved products occurred out of each pore.
Perovskite-type structured LaCoO3 fine powder with high surface areas could be prepared by a polymer precursor method using acetylacetone (AcAc) as a chelating agent at 500°C. This fine powder could be used for an electrophoretic deposition (EPD) process in an acetylacetone-based suspension. The LaCoO3 fine powder supported on carbon-cross device was prepared by the EPD method without a sintering process. The device showed good properties of amperometric sensing of hydrogen-phosphate ion.
Dog-bone shaped specimens of Cu foils were fabricated by a combination of electrodeposition and photolithography to investigate the effect of electrochemical condition on mechanical properties of the foils. Electrodeposition of Cu was conducted on a substrate with a dog-bone shaped metallic surface from an acidic CuSO4 solution at a constant current density. Mechanical properties of the Cu foils were investigated by tensile test. From the results of the test, we found that tensile strength was increased but strain to failure was decreased with increasing current density. In addition, SEM observations for the Cu specimens prepared with different current densities revealed that the crystalline size became smaller with increase in current density till it reached a value. We concluded that mechanical properties of the Cu foils are related to the grain size of the Cu deposits.
Fe–Pt nanoparticles fabricated by the polyol process have been reported as a possible alternative material for use in catalytic electrodes for polymer electrolyte fuel cells (PEFCs). Catalytic Fe–Pt alloys suffer from a problem where Fe dissolves from the alloy. Here, we examined the dissolution of Fe into the electrolyte for various composition ratios of Fe to Pt. We have also described the characteristics of Fe–Pt nanoparticles on the basis of XRD, XRF, TEM-EDX and electrochemical measurements and have discussed the rinse effect of Fe–Pt nanoparticles in acid solutions and the annealing effect of Fe–Pt caused by structural phase transitions from disordered fcc to ordered fct phase structures.
Pt nanoparticles were photocatalytically deposited onto TiO2 to improve the photocatalytic remote oxidation activity. Among the conditions examined, deposition from 1–3 mM H2PtCl6 solution for 2–10 s gave the highest activity. Further deposition resulted in reduced activities, possibly due to overgrowth of the Pt nanoparticles. The average size of the Pt nanoparticles on the optimized photocatalyst was 2.7 nm. When the most active Pt-modified TiO2 was used, it took 50 s to make an octadecyltriethoxysilane-modified glass surface superhydrophilic by the remote oxidation (light intensity was 200 mW cm−2 and the gap between the photocatalyst and the glass surface was 7.5 µm).
Selective determination of uric acid (UA) was conducted in the presence of ascorbic acid (AA) and acetaminophen (APAP) as interference species at an unmodified glassy carbon paste electrode (GCPE). Using the GCPE prepared in our lab, we succeeded in detecting UA in the presence of AA in acidic and alkaline media. The oxidation peak potential of APAP is very close to that of UA in neutral media, but in alkaline media, a peak separation of ca. 140 mV was obtained between UA and APAP on the differential pulse voltammogram. Moreover, voltammetric determination of tryptophan (Trp) and serotonin (5-HT) was successfully conducted by analyzing the redox peaks of their oxidation products at GCPEs in phosphate buffer solutions in the presence of interferences. The oxidation products of Trp and 5-HT provided redox couples at more negative potentials than for that of the interferences: 5-fold tyrosine (Tyr) did not hinder the determination of Trp, and 200-fold uric acid (UA) and acetaminophen (APAP) did not hinder the determination of 5-HT. In all samples studied in this research, glassy carbon paste electrodes were fairly better than graphite paste electrode.
Effects of reaction conditions on size-selective photoetching of CdTe nanocrystals were presented focusing on electron mediator and wavelength of irradiating light. Methyl viologen, which was expected to work as an electron mediator of photo-induced oxygen reduction accelerating the photoetching, decreased significantly the rate of the reaction. The results are compared with the photoetching of CdS nanocrystals in terms of overpotential for oxygen reduction and adsorption of electron mediators on nanocrystals. Under optimized conditions, the photoetching can produce highly monodispersed nanocrystals having fluorescence peak of fwhm value as small as 23.5 nm around the wavelength region where CdTe nanocrystals are stably produced by the conventional synthesis. However, further blue shifts of irradiating light gradually increased the fluorescence fwhm value, and the exciton peaks became unclear as well. The results were considered by comparing with recently reported magic-sized nanoclusters.
We prepared a microfluidic device with an interdigitated array electrode modified with antibodies to develop immunosensors. A comb-type array (W1) was used for forming immunocomplexes and another (W2) for detecting mediators generated by the enzyme reaction. We used electropolymerization and avidin-biotin complexes for an addressable immobilization of antibodies on W1. Since the microfluidics significantly accelerated the formation of the immunocomplexes, a period as short as 10 min was sufficient to detect the responses. The current observed at bare array (W2) increased with increasing analyte (mouse IgG) concentration in the range of 1.0–100 ng/mL. Therefore, present procedure is suitable for rapid immunosensing in a simple device.
Organic thin film solar cells composed of the hetero-deposited Langmuir-Blodgett (LB) films were fabricated using poly(3-hexylthiophene) (P3HT) as a donor, [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an acceptor and poly(N-dodecylacrylamide) (pDDA) as an amphiphilic polymer. Various types of the solar cell such as the bulk heterojunction (BHJ) type, p-n heterojunction type, double layer BHJ type and P3HT single layer type solar cells were constructed and their photovoltaic properties were compared with them. The short circuit current densities observed at all the solar cells fabricated by LB technique were three orders of magnitude smaller than that of BHJ solar cell fabricated by spin-coating method because of the film resistance of the existence of pDDA for forming LB film. The open circuit voltage is interestingly obtained to be 1.23, 0.82 and 1.06 V at the P3HT single layer type, p-n heterojunction type and the double layer BHJ type solar cells fabricated by LB technique, resulting to be higher than 0.52 V at the BHJ type solar cell. The phenomena demonstrate that the hole produced by photoinduced charge separation can be accumulated at the P3HT layer of the solar cells.