A wearable optical topography system was developed that is based on near-infrared spectroscopy (NIRS) for observing brain activity noninvasively including in regions covered by hair. An avalanche photo diode, high voltage dc-dc converter, and preamplifier were placed in an electrically shielded case to be safely mounted on the head. Rubber teeth and a glass rod were prepared to clear away hair and reach the scalp. These devices realized for the first time a wearable NIRS imager for any region of the cortex. The activity in the motor cortex during finger tapping was successfully observed.

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Gallium-doped zinc oxide (GZO) nanoparticles (NPs) have been synthesized by a solvothermal synthesis method using gallium chloride and zinc chloride as precursors in anhydrous methanol along with bases. Systematic investigations have revealed that H2O, formed through the condensation of metal hydroxides to obtain GZO NPs, not only enhances the production of layered compounds as byproducts but also accelerates Ostwald ripening to reduce the amount of doped gallium ions. To overcome H2O generation during NP growth, we first applied sodium methoxide (NaOMe) as a base for the synthesis of GZO NPs. As a result, high-performance GZO NPs were successfully obtained in a single phase, and the mean particle size of the GZO NPs was controlled from 10 to 35 nm by changing the molar ratio of the sodium hydroxide (NaOH) and NaOMe in the reaction mixture. We further applied the obtained GZO NPs to prepare GZO NP-based transparent conductive metal oxide (TCO) films using an NP-mist deposition strategy as our developed NP-coating method on substrates. The resistivity and transparency of the deposited GZO thin films were compared with those of conventional thin films prepared by a dispersion coating method, showing that NP-mist deposition is a promising method for fabricating high-performance GZO NP-based TCO thin films on substrates under mild atmospheric conditions.

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Current–voltage (I–V) characteristics and their temperature dependence, of Schottky and metal-insulator-semiconductor diodes with tunnel thin insulating layers, are theoretically and experimentally studied. The effective barrier height of a Schottky diode becomes low and strongly dependent upon the applied voltage, when the impurity density of the semiconductor increases such that the tunnel current dominates the total curent. The I–V curves and their temperature dependence, of the tunnel thin MIS diodes strongly reflect the characteristics of the Schottky diodes, although the insulating layers suppress the currents, depending upon their I-layers thickness.

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Schottky barrier heights of Ni/n-GaAs junctions were controlled by changing the pH of pretreatment chemicals. An effective barrier height of 0.8 eV was obtained by treatment with dilute HCl liquid (pH = l), and 0.6 eV by treatment with dilute NH4OH liquid (pH = 13). Surface analysis by an x-ray photoelectron spectroscopy indicated the existence of about twice the density of oxygen at the surface of the HCl-treated wafer as compared with that pretreated by the NH4OH liquid. The former shows nearly linear C -2–V characteristics, while the latter shows larger but less frequency dependent capacitances. Two levels of Ni/n-GaAs Schottky barriers were formed on a wafer by successive pretreatments and selective Ni evaporations.

Mass sensors based on the eigenmode shift of coupled cantilevers achieve much higher sensitivity than those based on the single cantilever’s eigenfrequency shift. In the former sensors, two identical cantilevers and a weak coupling stiffness between them are required to achieve high sensitivity. However, conventional coupled cantilevers cannot satisfy these requirements because of machining accuracy. To satisfy both requirements, a virtual coupling between a real macrocantilever and a virtual cantilever, whose dynamics was calculated using a digital computer, was proposed in our previous research. The sensitive mass sensing of mg-order masses was achieved. In the present work, for minute mass sensing, we replace the real macrocantilever with a real microcantilever. The calculation speed of a digital computer is not fast enough to calculate the virtual cantilever’s dynamics because the natural frequency of the microcantilver is much higher than that of the macrocantilever. Therefore, we use an analog circuit instead of a digital computer to achieve virtual coupling with the virtual cantilever. The proposed system enables us to tune the virtual cantilever’s parameters to satisfy both requirements for high sensitivity by changing the analog circuit parameters. We verified experimentally that the proposed system achieved high sensitivity for mass sensing of the order of nanograms.