Shinriki Teii

Surface Catalytic Effect of Electrode Materials on Ozone Dissociation in a Cylindrical Dielectric Barrier Discharge Ozonizer

The effect of electrode materials on ozone dissociation is studied by using the electrodes made of stainless steel, copper, and carbon in a coaxial cylindrical-type dielectric barrier discharge ozonizer. The gas and electrode surface temperatures as well as the ozone concentration generated in the ozonizer are measured with varying the applied pulse voltage. The results show that the surface temperature for a stainless steel electrode decreases sharply by more than 10°C as the discharge begins to generate ozone. This is explained reasonably by the dissociation of ozone at the catalytic stainless steel electrode surface, which takes away a large amount of heat from the electrode surface. The decrease of temperature for the less catalytic copper electrode is only about 3°C , and the temperature remains almost unchanged for the noncatalytic carbon electrode. Moreover, the ozone concentrations with the copper and carbon electrodes are approximately twice as high as that with the stainless steel electrode at the same voltage. This is attributed to a decrease in catalytic dissociation of ozone at the copper and carbon electrode surfaces, thus affecting the ozone yield.

Role of Hydrogen in Ultrananocrystalline Diamond Deposition From Argon-Rich Microwave Plasmas

A two-step process consisting of an initial nucleation stage with hydrogen followed by a growth stage without hydrogen is used to examine the role of hydrogen in ultrananocrystalline diamond deposition in Ar-rich microwave plasmas. An addition of 5% of H2 to Ar-rich/CH4 in the initial stage increases the nucleation density (up to 109 cm-2) and the mean grain size (around 10 nm), accompanied by some improvement of crystallinity. However, an addition of H2 above 10% suppresses nucleation by the etching of nucleation sites. The introduction of hydrogen atoms promotes the termination and stabilization of diamond grain surfaces toward sp3 configuration, which are responsible for enhancing nucleation and crystallization. In contrast, Ar promotes renucleation by increasing the production of C2 radicals in the plasma, which causes the degradation of the stabilization on the growing surfaces.

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.

Electron energy distribution in nitrogen plasma in various discharges

Electron energy distribution in nitrogen plasma is studied to clarify the condition of dip formation by the resonant vibrational excitation of N 2 in several types of discharges: in diffusion and glow plasmas in a glass tube, in a multipole minimum-B type plasma, in diffusion and glow mode plasmas in a large volume space chamber and in an electron cyclotron resonance plasma. It is found that the dip appears when the mean energy of thermal electrons is in a range from 0.8 to a few eV. When the mean energy is lower than 0.5 eV or higher than 8 eV, the dip is not detectable. Mechanism of the dip formation is discussed and the depth of the dip is compared with previous theoretical results.

Time- and space-resolved electric potentials in a parallel-plate radio-frequency plasma

A low-input capacitance emissive probe heated by a CO2 laser has been used to investigate frequency-modulated electric potentials in a radio-frequency (rf) glow discharge plasma. An excellent time-response ability of our probe system to a sharp potential change was confirmed by potential measurements with applying a step function voltage to the plasma. The electric field distribution as the first derivative of the potential distribution obtained by the probe method was compared with that by the laser optogalvanic spectroscopy to ensure the reliability of the measurements in the sheath region. The probe method was applied to directly monitor a temporal variation of axial potential and electric field distributions between two parallel-plate electrodes in a rf argon plasma. The formation of ion sheath regions on both electrode surfaces was confirmed at any phase in a rf cycle. The results were consistent with a one-dimensional model for potential and electric field distributions in the sheath region.

Argon dilution effects on diamond deposition in electron cyclotron resonance plasma: a double probe study

Abstract The Ar dilution effects on diamond deposition at moderate pressures (26.6–400 Pa) in an electron cyclotron resonance hydrogen-methane plasma have been studied in connection with electron temperature (Te) and electron density (ne). The double probe measurement revealed the dependence of Te and ne on Ar concentration, pressure, and microwave power. Te decreased in proportion to Ar concentration and was in the range of 3.7–7.5 eV. In contrast, ne exhibited only a small change with increasing Ar concentration except at a higher pressure and was on the order of 1010–1011 cm−3. The Ar dilution promoted nucleation rather than growth, as shown by an increase in nucleation density and renucleation on preexisting diamond grains. The mechanism leading to the peaked growth rate at 33–50 vol.% Ar was explained by the variation of the ion-bombardment energy and the fluxes of radicals, based on the measured Te and ne.

High quality railgun HYPAC for hypervelocity impact experiments

Abstract The characteristic of a very high quality railgun HYPAC (10 kV, 6,000 μ F, 300 kJ) at the Institute of Space and Astronautical Science (ISAS) which is capable of accelerating a 1–2 gram projectile of 10–20 mm diameter made of polycarbonate to a hypervelocity of 7.8 km/sec and its utilization in hypervelocity impact experiments are reviewed. Also shown are further efforts to increase the velocity, to improve the quality of the projectile such as the acceleration of metal powder and to explore a new application of this facility.

Isotope effects in amorphous silicon thin films produced by Ar‐SiH4 ‐D2 plasma chemical vapor deposition method

Ar‐SiH4 ‐D2 gas mixture positive column plasmas and the deposition of (a‐Si:D/H) thin films are investigated. Deuterated amorphous silicon thin films (a‐Si:D/H) are produced in an Ar(95%)‐SiH4(2.5%) ‐D2(2.5%) mixed gas plasma by employing dc positive column plasma chemical vapor deposition techniques. A twin probe electric field measurement is used to determine the plasma parameters. The reaction chamber wall temperature is measured by an infrared (IR) image camera. The results indicate that the uniformity of plasma is excellent; the wall temperature of the reaction chamber is nonuniform; and the deposition rate increases with increasing discharge power and gas pressure. The optical characteristics of isotopically different a‐Si:H/a‐Si:D films are also studied. The results show that the optical band gap of a film has a nonmonotonic thickness dependence with a significant isotope effect.

Numerical Study on Heat Flow During Catalytic Dissociation of Ozone in a Dielectric Barrier Discharge Ozonizer

A simple heat flow model is established for numerical analysis of the effect of catalytic dissociation of ozone on electrode surface temperature in a coaxial cylindrical-type dielectric barrier discharge ozonizer. The amount of heat consumed by the ozone decomposition at the electrode surface is determined from the balance of heat flow among the discharge gas, electrode, and cooling water. Our calculation using the experimental data shows that the ozone decomposition by 1.6% in total ozone reaching the electrode surface is required to explain the observed temperature decrease from about 20 °C to 8 °C for a stainless steel electrode, while that by 4.5% is needed to explain the temperature decrease from about 20 °C to 19 °C for a copper electrode. The decomposition rates calculated in the discharge are about two orders of magnitude higher than those measured in gas flow downstream of a similar discharge.

Wettability of Amorphous Diamond-Like Carbons Deposited on Si and PMMA in Pulse-Modulated Plasmas

Pulse-modulated direct-current methane plasmas are used to deposit amorphous diamond-like carbon films on Si and dentistry-use polymethyl methacrylate (PMMA) substrates as a function of the negative pulse voltage applied to the substrate (Vmax). The films on PMMA show a transition from diamond-like to more graphitic carbon in the Raman spectra with increasing Vmax, dissimilar to those on Si. This is attributed to easy deformation of PMMA, leading to the low compressive stress of the films (1 to 2 GPa). The contact angle of water for the films on both Si and PMMA is large, ranging from 79° to 94° almost independent of Vmax, confirming that the films are hydrophobic despite the difference in carbon bonding state. The large dispersion component (41-43 mJ/m2) of the surface free energy of the films measured from the contact angle of water and 1-bromonaphthalene indicates the high mass density of the films. The small polar component (0.2-3.5 mJ/m2) is attributed to hydrogen saturation of the surface sites forming nonpolar C-H bonds and, thus, responsible for the hydrophobic behavior.