Kazuhiko Tonooka

Photovoltaic effect observed in transparent p–n heterojunctions based on oxide semiconductors

Abstract Transparent p–n junctions composed of zinc oxide, copper-aluminum oxide and indium-tin oxide films were fabricated by pulsed laser deposition on glass substrates at temperatures as low as 400 °C. Diode characteristics in the current–voltage response and the photovoltaic effect were observed for the junctions fabricated. The photovoltaic junction had an optical transparency of more than 43% for the wavelengths λ>500 nm, and exhibited photovoltage as large as 80 mV when it was illuminated by a LED of λ≈470 nm. The properties of the photovoltaic transparent junction seemed to be degraded by the inadequate crystallinity of the copper-aluminum oxide layer. The ZnO/CuAlO/ITO/glass structure developed in this study has demonstrated a possible application of transparent solar cells.

Properties of copper-aluminum oxide films prepared by solution methods

Abstract Conducting copper–aluminum oxide films have been prepared by employing the dip-coating method. Metal alkoxides and nitrates were examined as metal sources in the precursor solutions for the preparation of CuAlO 2 samples based on the procedures of sol–gel and nitrate processes, respectively. Fired samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis and electrical measurements. Properties of the samples depended on the calcination temperature and the composition of the precursor solution. Electrical conductance of the samples corresponds well with the delafossite CuAlO 2 content, which was determined by the intensity of corresponding lines in the XRD patterns. The lowest sheet resistance (≈45 Ω/□) was obtained for a film sample prepared by the nitrate process followed by a calcination at 1100 °C for 4 h in air.

Analysis of blood pulse wave measured by reflective optical sensor

Spectrum analysis of a blood pulse wave (BPW) has been carried out by a novel optical measurement system. The BPW is detected at the second finger of a left hand by a photoelectric plethysmography. Spectrum analysis of the BPW reveals two independent signals, which are at about 1 Hz and 0.1 Hz. The higher-frequency signal is due to heart beats, and the lower signal is the result of breath. The BPW spectrum has been investigated in terms of frequency stability of heart rate (HR). The correlation coefficient between HR and standard deviation of HR in the amplitude spectrum is -0.90. The standard deviation of BPW in amplitude spectrum is presented as a parameter of the cardiovascular system.<<ETX>>

Growth and superconductivity of niobium titanium alloy thin films on strontium titanate (001) single-crystal substrates for superconducting joints

Aiming to introduce NbTi alloy superconducting joints for REBa2Cu3O7−δ (REBCO, RE: rare-earth element) superconducting wires, NbTi alloy thin films were deposited at room temperature on SrTiO3 (STO) (001) single-crystal substrates, which have a high lattice matching with REBCO (001). The strain, crystallinity, surface morphology, and superconducting property of the films with various thicknesses were investigated. The NbTi films grew in the orientation with (110)NbTi//(001)STO:[001]NbTi and [11–0] NbTi//[100]STO; that is, the NbTi lattices had two directions in the (110) of NbTi. The strain decreased and the crystallinity improved as the film thickness increased. The films were found to crystallize immediately at the interface between the films and substrates by cross-sectional scanning transmission electron microscopy. The flat surfaces of the films have mesh-like morphologies due to the growth of elongated NbTi grains along the [100] and [010] of the STO, reflecting the in-plane two directions of the NbTi lattices. The superconducting transition temperature of the films increased with improvement in the crystallinity of the films. The preparation of superconducting NbTi alloy thin films with sufficient crystallinity at room temperature suggested the possibility of forming the films on REBCO and the applicability of the films as superconducting joints.