Fumiaki Mitsugi

Pulsed laser deposited WO3 thin films for gas sensor

Abstract WO 3 has attracted attention because of its potential for NO x gas sensing. Thin films of WO 3− x were prepared by KrF excimer pulsed laser deposition technique on quartz and Al 2 O 3 with Pt electrode. The films were deposited at various substrate temperature, oxygen pressure and conditions of the post-annealing. The substrate temperature over 400 °C was needed for the crystallization of the WO 3− x thin film. The crystal structure of the WO 3− x thin film deposited at oxygen pressure of 100 mTorr and the substrate temperature of 400 °C was tetragonal phase, however, the films deposited at the oxygen pressure over 200 mTorr showed triclinic phase. The atomic force microscopy image of the WO 3− x thin film post-annealed in oxygen atmosphere for 30 min showed an average grain size of 268 nm. It was approximately two times larger than that of the as-deposited film. The maximum sensitivity ( R NO / R N 2 ) of the as-deposited triclinic WO 3− x thin film gas sensor in the NO gas (60 ppm in N 2 ) was 4.2 at an operating temperature of 200 °C.

WO3 thin films prepared by pulsed laser deposition

We report the structural and gas sensing properties of tungsten trioxide (WO3) thin films prepared by the KrF excimer pulsed laser deposition technique. The WO3 thin films having amorphous, crystallized tetragonal and triclinic structures were fabricated at the oxygen pressure of 10–300 mTorr and the substrate temperature of 150–800°C. We revealed the effect of the oxygen pressure and substrate temperature during the deposition on the crystal phases of the WO3 thin films. The atomic force microscopy measurement shows that the average grain size and the average number of grains are approximately 200 nm and 8/µm2, respectively. The triclinic WO3 thin film with a thickness of 1 µm showed high sensitivity of 254 in NO (60 ppm) gas at a low operating temperature of 150°C.

Investigation of electric discharge sound in atmospheric pressure plasma using optical wave microphone

Abstract The light diffraction technique, which we call the “Optical Wave Microphone (OWM)” technique, is an effective sensing method to detect the sound and is flexible for practical uses as it involves only a simple optical lens system. This technique is also very useful to detect the sound wave without disturbing the sound field. Moreover, OWM can be used for sound field visualization by computerized tomography (CT) because the ultrasmall modulation by the sound field is integrated along the laser beam path. The characteristics of the coplanar DBD (Dielectric Barrier Discharge) operated in air is investigated. Applied voltage, current and the electrical discharge sound of coplanar DBD are measured, and examined the relationship between the micro discharge and the acoustic properties. We expect that understanding of acoustic properties gives more details of electric discharges. These are the first experiments to verify the feasibility of the OWM-CT method for the visualization of the sound field of DBD discharge.

Properties of soil treated with ozone generated by surface discharge

Chemical contamination in plants, soil, and ground water has become serious by overuse of pesticides and nitrogen fertilizers in agriculture. We propose the use of ozone generated by atmospheric pressure plasma for soil disinfection as one of the plasma applications into agriculture. Because ozone has strong oxidation potential to decompose organic substances in soil, it is considered to be one of the candidates as potential alternative to both pesticide and nitrogen fertilizer. In this paper, fundamental studies on changes in acidity and amounts of nitrogen nutrients, bacteria, mold, and soil DNA remained in soil after ozone treatment were carried out with a system using a quartz chamber. Surface barrier discharge that operates in atmospheric oxygen was used in the system as the ozone generator. In addition, growth of radishes that seeded on soils in pots that were treated by ozone diffusion method was also evaluated.

Ferroelectric and colossal magnetoresistive properties of a PbZr1-xTixO3/La1-xSrxMnO3 heterostructure film

We report the ferroelectric and magnetoresistive properties and crystallization of a PbZr0.52Ti0.48O3 (PZT)/La0.8Sr0.2MnO3 (LSMO) heterostructure film prepared by pulsed-laser deposition on a MgO(100) single crystal substrate. Ferroelectric properties such as the hysteresis loop and dielectric constant of the Au/PZT/LSMO capacitor were compared with those of the Au/PZT/YBa2Cu3O7-x (YBCO) superconductor heterostructure film. The resistivity of the LSMO film was as low as that of the YBCO film at room temperature. The fabricated Au/PZT/LSMO capacitor had a remanent polarization of 29 µC/cm2, a coercive field of 30 kV/cm and a dielectric constant of about 1000.

Gas flow dependence on dynamic behavior of serpentine plasma in gliding arc discharge system

Gliding arc discharge systems have been used in various applications. However, the power of conventional gliding arc plasmas is relatively high and the system requires an additional discharge for its ignition and a resistor for current protection, which causes further total energy consumption. We have proposed ultraviolet (UV)-assisted gliding arc discharge systems supported by time-resolved understanding for electrical characteristics and dynamic behavior of serpentine plasmas. In this paper, we report on gas flow dependence on dynamic behavior of serpentine plasmas in a gliding arc discharge system with the irradiation of a low-pressure mercury lamp. Time-resolved evaluation was carried out using the results of synchronized measurement for serpentine plasmas with a high-speed camera, a high-voltage probe, and a current sensor. Waveforms and mean values of the applied voltage, current, power, impedance, and energy for serpentine plasmas in the UV-assisted gliding arc discharge system were studied. The power and impedance per unit plasma length were also evaluated.

Investigation of electric discharge sound in atmospheric pressure plasma

Abstract The characteristics of the Coplanar DBD (Dielectric Barrier Discharge) operated in air, argon or helium are investigated. Applied voltage, current and the electrical discharge sound of Coplanar DBD discharge are measured, and examined the fundamental relationship between the micro discharge and the acoustic properties. We expect that the understanding of acoustic properties gives more details of electric discharges and also develops new applications in the field of medical diagnostics, environment system, etc. We apply the new method to examine the electric discharge sound using Fraunhofer diffraction effect of visible laser beam. This new system is called the optical wave microphone by us and is very useful for the detection of sound wave without disturbing the sound field. The Fast Fourier Transform (FFT) is applied to discriminate the acoustic sound of the Coplanar DBD discharge and the dominant frequency components.

Fundamental Study on Ozone Treatment of Soil for Agricultural Application

In this study, influence of ozone treatment on physical properties of soil was investigated. We used a quartz container for ozone treatment of soil. The amount of soil used for ozone treatment was 300 g. Treating time was 30 min. Flow rate of ozone gas was 1.5 L/min. We measured characteristics of soil such as pH(H2O) and inorganic nutrient content (NO3-N, NO2-N and NH4-N) before and after ozone treatment. Exhaust ozone concentration from the quartz container was monitored with an ozone monitor. The temperature of soil was measured with a thermo-couple during treatment. Ozone amount reacted with soil was about 0.99 g when soil was stirred. Ozone amount was about 0.82 g when soil was not stirred. Contents of NO3-N and NH4-N increased by one order after treatment and subsequently kept a constant quantity. The pH(H2O) decreased drastically to strong acidic region (pH(H2O)=5.0) just after ozone treatment, which is too acidic for growth of crops. However, the pH(H2O) value recovered gradually with time.

Angular behaviour of critical current density in YBa2Cu3O y thin films with crossed columnar defects

Columnar defects (CDs) were installed into YBa2Cu3O y thin films at the crossing angle ±θ i relative to the c-axis using 200 MeV Xe ions, in order to clarify the influence of ±θ i on the angular behaviours of critical current density J c. The width of a J c peak occuring at B || c linearly increases with broadening CD-crossing angle, where its shape maintains a single peak in the range of θ i ≤ ±25°. The CDs crossing at ±45°, on the other hand, drastically change the angular behaviour of J c around B || c: the J c is equally elevated over the angular region from −45° to 45° in the lower magnetic field, whereas the rapid reduction of the J c occurs at B || c with increasing magnetic field, leading to the appearance of double peaks near the irradiation angles, ±45°. This crossover phenomenon is attributed to the difference in the pinned states of flux lines between B || c and at the irradiation angles: the CDs crossing at ±45° cannot provide the correlated flux pinning along the c-axis, resulting in the uncorrelated pinned state at B || c.

Study on ozone treatment of soil for agricultural application of surface dielectric barrier discharge

Recently, application of plasma technologies to the agricultural field has attracted much interest because residual pesticides and excessive nitrogen oxides contained in plants, soil, and groundwater have become a serious issue worldwide. Since almost all of the atmospheric discharge plasma generates ozone, the effects of ozone are among the key factors for their agricultural applications. We have proposed the use of ozone generated using surface barrier discharge plasma for soil disinfection or sterilization. In this work, the ozone consumption coefficient and diffusion coefficient in soil were measured by the ultraviolet absorption method. The pH(H2O) and amount of nitrogen nutrient in soil after ozone diffusion treatment were studied and plant growth was observed simultaneously. The effect of ozone treatment on the amount of DNA in soil was also investigated and compared with that determined from the obtained ozone consumption coefficient.