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A metal nanomesh electrode has the potential to realize a low-resistive, rare-metal-free transparent electrode. However, the electrical resistivity has not been measured as yet. We fabricated metal nanomesh electrodes and their electrical resistivity was obtained by measuring the current–voltage characteristics. Comparing with the calculated values of the microapertures, the electrical resistivity of the nanomesh electrode tended to deviate from the calculated values with reduction of the aperture interval and increase of the aperture density. This deviation was considered to be the effect of narrowing the conduction path of electrons and increasing the electron scattering probability by the nanoapertures. The order of the resistivity of the nanomesh electrodes was 10−6–10−5 Ω cm, one order of magnitude lower than that of conventional transparent oxides such as indium tin oxide.

Attention has been focused recently on the harmful effects and malodor of sulfuric compounds; therefore, various laws have been enacted to regulate environmental concentration and use of most sulfuric compounds. In order to avoid sulfuric malodor, a reasonable, easy, sensitive, and selective measuring method to detect sulfuric compounds is required. In this research, we adopted the specific adsorption of sulfuric compounds to a metal surface as a sensing principle. It was suggested that polarization is an important factor of molecular recognition from results obtained by quartz crystal microbalance (QCM), ellipsometry, and stripping voltammetry (SV). Therefore, we used cyclic surface polarization impedance (cSPI), based on electrochemical impedance spectroscopy (EIS) under the dynamic control of an electrode potential and a constant phase element (CPE) impedance, as a detecting method for sulfuric compounds. As a result, we could detect three sulfuric compounds, hydrogen sulfide, methyl mercaptan, and dimethyl sulfide, with this method at sub ppb levels and discriminate the three sulfuric compounds. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A biological olfaction system is one of the highest performance chemical sensing systems for low-molecular-weight compounds. An ability of recognizing a various molecular properties based on their structures is essential for a biological odor recognition process. For the development of a sensor mimicking the olfactory system, we have formed benzene-patterned self-assembled monolayer (SAM) on the sensor surface using SAMs with nanostructure that serves as adsorption sites for benzene ring, which is representative substructure of aromatics. The structure of the benzene-patterned SAM surface was analyzed by contact-angle measurement, ellipsometry, cyclic voltammetry (CV) and atomic force microscopy (AFM). Moreover, the electrodes evaluated as sensor surfaces with cyclic surface-polarization impedance (cSPI) sensor that measures changes in impedance of the electrode surface by adsorption of substances. The results of cSPI indicated the benzene-patterned SAM surface could distinguish benzene by recognizing of the hydrophobicity and the molecular size.

The global demands for landmine abolition become stronger, whereas the development of landmine detection technology progresses slowly. At present, the detection activities are mainly performed by means of a metal detector or a well-trained dog that needs much time and cost. Therefore, a more efficient landmine detection technique is desired. Most landmines contain aromatic nitro compounds, such as 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) as explosive charges; therefore, these substances are clues for landmines. In this study, we tried to detect amount of aromatic nitro compounds high-sensitively using a surface-polarization controlling method that measures electrochemical impedance of an electrode surface where explosive compounds adsorbed. As a result, we could detect the aromatic nitro compounds at detection limits of sub-μM level and distinguish the aromatic nitro compounds from other aromatic compounds at 100 μM at least. Furthermore, in order to improve specificity and sensitivity to aromatic nitro compounds, the electrode surface was modified with arenes that makes charge-transfer complex with aromatic nitro compounds. We adopted anthracene as the arene to functionalize the electrode surface. The modified electrode makes it possible to detect the aromatic nitro compounds selectively. This method enables us to develop a sensor for landmine detection.

A thin metal film with nano-apertures, called “nano-mesh electrode,” generates near-field lights near the electrode. We investigated carrier excitations in semiconductors by the near-field light. Finite-difference time-domain (FDTD) method revealed that when the infrared light irradiates the Au nano-mesh electrode on Ge, near-field lights are generated and absorbed in the surface region of the Ge. In order to measure the photocurrent involved by near-filed lights, we fabricated a Schottky cell and applied a Au nano-mesh electrode on the n-type Ge. The efficiency of the Schottky cell with the Au nano-mesh electrode improved in infrared region compared to plain the Au-film Schottky cell. The agreement between theoretical simulations and experiments indicates that near-field lights enhance the carrier excitation in the semiconductor.

Electron acceptor molecules form charge transfer (CT) complexes with electron donors. CT complexes are known as an organic conductive material. In this report, we suggest a nanowire sensor to detect electron-acceptive aromatic nitro compounds by conductance switching brought on by charge transfer interaction. The sensor surface possesses a molecular wire network formed by bridging nanogaps between Au nanoparticles (Au-NPs) with electron donor oligothiophene. The Au-NPs were fabricated by sputter deposition with controlling the particle-size and the gap-size. We confirmed the oligothiophene bridging by resistivity and the formation of CT interaction between oligothiophene and electron acceptors by fluorescence quenching. The conductance of the sensor electrode was increased by adsorption of electron acceptors, such as iodine and aromatic nitro compounds.

Recently, the electrical characteristics of metal-molecule-metal nanowires are studied. Interaction between the junction molecule and the analytes will affect the molecular orbital that alters a conductive path. We have been interested in charge transfer (CT) interaction that induces the partial transfer of electron from an electron donor to an electron acceptor. The measurement result obtained with crossed-wire tunneling junction indicated that the CT interaction provides a significant conductance change of the junction molecule. In this report, we suggest a nanowire sensor to detect volatile organic compounds (VOC) by conductance switching brought on by the charge transfer interaction. The sensor surface possesses a molecular wire network formed by bridging nanogaps between Au nanoparticles (Au-NPs) with electron donor molecules. The Au-NPs were fabricated by sputter deposition with controlling the particle-size and the gap-size. We confirmed the donor oligothiophene bridging by resistance transition and the formation of CT interaction between oligothiophene and analytes by fluorescence quenching. The conductance of the sensor electrode increased by adsorption of electron acceptors, such as iodine and aromatic nitro compounds.

A sensitive landmine detection method with easy operation is demanded, however, sensors satisfied both sensitivity and ease have not been developed yet. The purpose of this study is to develop the high-sensitive chemical sensor that can easily and quickly identify the explosive molecules leaking from landmines. It is conceivable that such technology could be applied to a sensor for security. In this paper, we describe a sensor using a surface polarization controlling method. We improved specificity and sensitivity to aromatic nitro compounds by introducing the modified electrode with Lewis base that has the charge-transfer interaction with aromatic nitro compounds. Furthermore, the modified electrode could be characterized with fluorescence spectroscopy.

A novel transparent aluminum nanomesh electrode with nanoapartures smaller than the wavelength of the light was proposed. Unlike conventional conducting oxides such as indium tin oxide, it has the potential to realize a rare-metal-free and low-resistivity transparent electrode. It was fabricated by nanopatterning with our embedded particle monolayer method, which enables the formation of a self-assembled particle monolayer over a large area, and its optical properties were investigated. As a result, the transmittance of the fabricated aluminum nanomesh electrode was found to be more than 55% at the peak wavelength when the opening ratio was 47%.