Taiki Ito

Control of reactive oxygen and nitrogen species production in liquid by nonthermal plasma jet with controlled surrounding gas

We present the development of a low-frequency nonthermal plasma-jet system, where the surrounding-gas condition of the plasma jet is precisely controlled in open air. By restricting the mixing of the ambient air into the plasma jet, the plasma jet can be selectively changed from a N2 main discharge to an O2 main discharge even in open air. In the plasma-jet system with the controlled surrounding gas, the production of reactive oxygen and nitrogen species is successfully controlled in deionized water: the concentration ratio of NO2 − to H2O2 is tuned from 0 to 0.18, and a high NO2 − concentration ratio is obtained at a N2 gas ratio of 0.80 relative to the total N2/O2 gas mixture in the main discharge gas. We also find that the NO2 − concentration is much higher in the plasma-activated medium than in the plasma-activated deionized water, which is mainly explained by the contribution of amino acids to NO2 − generation in the medium.

Effects of nonthermal plasma jet irradiation on the selective production of H2O2 and NO2− in liquid water

We present the effects of the application of a nonthermal plasma jet to a liquid surface on H2O2 and NO2− generation in the liquid. Two distinct plasma irradiation conditions, with plasma contact and with no observable plasma contact with the liquid surface, were precisely compared. When the plasma was made to touch the liquid surface, the H2O2 concentration of the plasma-treated water was much higher than the NO2− concentration. In contrast, when no observable contact of the plasma with the liquid surface occurred, the ratio of the NO2− to H2O2 concentration became over 1 and NO2− became more dominant than H2O2 in the plasma-treated water. Our experiments clearly show that reactive oxygen and nitrogen species can be selectively produced in liquid using appropriate plasma-irradiation conditions of the liquid surface. The ratio of NO2− to H2O2 was controlled within a wide range of 0.02–1.2 simply by changing the plasma-irradiation distance from the liquid surface.

Preparation and Characterization of High Quality Lead-free BiFeO3 Thin Films by Sputtering Process

BiFeO3 (BFO) thin films have been prepared on SrTiO3 (001) single crystal substrates by sputtering process which is suitable for mass production. Domain structure can be controlled by off-cut angle and direction of SrTiO3 substrates. A lateral PFM and a XRD reciprocal space mapping results reveal the BFO thin film on SrTiO3 (001) with 4° off-cut along [110] is single domain. The single domain BFO shows well-saturated ferroelectric D-E hysteresis loops at R.T.

Development of a non-equilibrium 60 MHz plasma jet with a long discharge plume

High-frequency plasma jets driven by voltages in the frequency range of 6–60 MHz are developed. A long plasma jet, 40 mm in length, is successfully produced by using a pair of ring electrodes outside a quartz tube. The electrode pair consists of a wide power electrode and a narrow ground electrode that is positioned at the head of the tube. The ratio of the length of the ground electrode to the length of the power electrode must be small in order to produce long plasma jets. The high-frequency plasma jet is operated in a non-thermal-equilibrium state at a gas temperature of around 60 °C. Operation at the very-high-frequency of 60 MHz leads to a lower discharge voltage and lower electron energy compared to lower frequencies of 6 and 13.56 MHz. The ability of the very-high-frequency (60 MHz) plasma jet to produce reactive oxygen and nitrogen species in water is also investigated. High H2O2 and NO3− concentrations of more than 1 mmol/l are realized by irradiating 3 ml of deionized water with the plasma for a...

Current conduction in single-domain BiFeO3 thin films

Recently, the semiconducting characteristics of BiFeO3 thin films such as the photovoltaic effect or diode characteristics have been extensively investigated. However, the current conduction mechanism has not been completely clarified yet. In this study, the current conduction mechanism of the ideal BFO thin film, which has a single domain without conduction domain walls, such as 71 and 109° domain walls, has been investigated. The current density–electric field (J–E) characteristics of 100- to 1000-nm-thick BFO thin films and their temperature dependence in the range of 100–260 K have been carefully investigated. From these thickness and temperature dependences of the J–E characteristics, it can be concluded that the most probable mechanism of current conduction in the single-domain BFO thin film is space-charge-limited current (SCLC) with a shallow trap.

Spatio-temporal behaviors of atmospheric-pressure plasma jets for investigation of reactive-species production in liquid

Summary form only given. Medical treatments with non-equilibrium atmospheric-pressure plasma jets have attracted great interests due to significant medical effects including cancer therapy. For biomedical applications of the plasma jets, it is of great significance to understand interactions of the plasma jet with liquid because the cellular tissue is covered with aqueous solutions, and biological behaviors are induced by reactive oxygen and nitrogen species (RONS) in the aqueous solutions through interaction with plasma-jet systems. In this study, effects of the plasma contacting conditions with liquid surface (direct contact and non-contact to the liquid surface) on RONS production in aqueous solutions have been investigated through characterization of spatio-temporal behaviors of the plasma jets; high-speed image observations with intensified CCD (ICCD) camera, fluid dynamic characterization of gas flows with Schlieren method, and electrical characterization of the plasma-bullet propagation onto substances for explicit evaluation of the plasma-jet contacting states. Concentrations of H2O2 and NO2- in the aqueous solutions have been measured for comparison of the plasma contacting conditions with liquid surface (direct contact and non-contact to the liquid surface) and for evaluations of the biological effects. Additionally, experimental factors for controlling concentration ratio of H2O2 and NO2- in water will be presented.