Here are presented experiments on fine particles levitating in low-pressure weakly ionized plasmas under a vertical magnetic field. The magnetic field is useful to provide a vertically long cylindrical column of fine-particle clouds, yielding even string-shaped vertically aligned fine particles, under the double-plasma configuration. Measurements show that fine-particle clouds rotate in the azimuthal direction on the horizontal plane even in such a weak magnetic field that positive ions are slightly magnetized. With an increase of the magnetic field, the rotation speed increases, being followed by subsequent saturation. The rotation speed and direction can be controlled by varying radial plasma potential and/or density profiles. The rotation is induced under the condition that the interparticle distance is small enough for the strong Coulomb coupling among fine particles. A mechanism of the rotation could be explained by effects of ion motions on fine particles, which are modified in the presence of the vertical magnetic field.
The wave dispersion relation in a two-dimensional strongly coupled plasma crystal is studied by theoretical analysis and molecular dynamics simulation taking into account a constant magnetic field parallel to the crystal normal. The expression for the wave dispersion relation clearly shows that high-frequency and low-frequency branches exist as a result of the coupling of longitudinal and transverse modes due to the Lorenz force acting on the dust particles. The high-frequency and the low-frequency branches are found to belong to right-hand and left-hand polarized waves, respectively.
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.
We propose a novel method of oxide crystal growth via atomic-additive mediated amorphization. By utilizing this method, solid-phase crystallization (SPC) of ZnO from amorphous phase has been successfully demonstrated via nitrogen atom mediation. The resultant SPC-ZnO films are highly orientated and the crystallinity is higher than that of the films prepared by conventional sputtering. By using the SPC-ZnO as a buffer layer, the resistivity of ZnO:Al (AZO) films is drastically decreased. 20 nm-thick AZO films with a resistivity of 5 10-4 cm and an optical transmittance higher than 80% in a wide wavelength range of 400-2500 nm have been obtained.
The two-dimensional concentration distribution of reactive oxygen species (ROSs) transported through an agarose-film tissue phantom by atmospheric-pressure plasma-jet irradiation is visualized using a KI-starch gel reagent. Oxygen addition to helium enhances ROS transportation through the film. A radial ROS distribution pattern at the plasma-irradiated film surface changes into a doughnut-shaped pattern after passing through the film. The ROS transportation speed is 0.14–0.2 mm/min. We suggest that there are two types of ROS transportation pathways in the plasma-irradiated film: linear and circular. The majority of ROSs are transported through the circular pathway. ROS concentration distributions changed markedly with irradiation distance. Diffusive ROS transportation due to a concentration gradient is negligible in plasma-irradiated films.
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