arXiv subjects

Rikizo Hatakeyama

Publications and source records attributed to Rikizo Hatakeyama.

5 recordsLinked to original sources

arXiv2014

Green tea induced gold nanostar synthesis mediated by Ag(I) ions

We report a synthesis of tea components conjugated gold nanostars (AuNSs) with strong near infrared absorption by reducing an aqueous solution of chloroauric acid trihydrate via green tea in association with Ag(I) ions. Green tea acts as a reducing agent by providing electrons for the gold (III) reduction as well as a stabilizing agent by conjugating some of its components on the surfaces of AuNSs. Moreover, the Ag(I) ions play an important role in mediating the branched growth of the resultant AuNSs by inducing anisotropic growth on the surfaces of initially formed spherical gold nanoparticles.

cond-mat.mtrl-sci↗

arXiv2004

Electrostatic ion-cyclotron instabilities modified by the parallel and perpendicular plasma flow velocity shears

The external and independent control of plasma flow velocity shears parallel and perpendicular to magnetic field lines is realized using segmented collisionless-plasma sources. Electrostatic ion-cyclotron instabilities are observed to be suppressed by the perpendicular flow velocity shears, the suppression physics of which is found to be distinguished into two aspects. On the other hand, the parallel flow velocity shears are demonstrated to destabilize the ion-cyclotron instabilities depending on the sign of the parallel shear in the absence of field-aligned electron drift flow.

physics.plasm-ph↗

arXiv2004

Plasma production by helicon waves with single mode number in low magnetic fields

Radio-frequency discharges are performed in low magnetic fields (0-10 mT) using three types of helicon-wave exciting antennas with the azimuthal mode number of $|m|$ = 1. The most pronounced peak of plasma density is generated in the case of phased helical antenna at only a few mT, where the helicon wave with $|m| = 1$ is purely excited and propagates. An analysis based on the dispersion relation well explains the density-peak phenomenon in terms of the correspondence between the antenna one-wavelength and the helicon wavelength. The $m=+1$ helicon wave propagates even in high magnetic fields where the density peaks are not observed, but the $m=-1$ helicon wave disappers. It is expected theoretically that the $m=-1$ helicon wave shows cutoff behavior in a low density region, [M. Kramer, Phys. Plasmas 6, 1052 (1999)], and the cutoff of $m=-1$ helicon wave experimentally observed coincides with the calculated one.

physics.plasm-ph↗

arXiv2004

Polarization reversal of electron cyclotron wave due to radial boundary condition

Propagation and absorption of electromagnetic waves with electron cyclotron resonance (ECR) frequency are experimentally and theoretically investigated for the case of inhomogeneously magnetized plasma column with peripheral vacuum layer, when a left-hand polarized wave (LHPW) is selectively launched. The polarization reversal from the LHPW to the right-hand polarized wave is found to occur near the ECR point. As a result, it is clarified that the LHPW, which has been considered not to be absorbed at the ECR point, is absorbed near the ECR point. The phenomena can be explained by taking into account the effects of the radial boundary conditions. In addition, it is found that the polarization reversal point can be adjusted by the external parameters, for example, plasma radius.

physics.plasm-ph↗

arXiv2004

Fluctuation-phase relation between positive and negative ions on pair-plasma electrostatic waves

Three kinds of electrostatic modes are experimentally observed to propagate along magnetic-field lines for the first time in the pair-ion plasma consisting of only positive and negative fullerene ions with an equal mass. It is found that phase lags between the density fluctuations of positive and negative ions vary from 0 to $π$ depending on the frequency and is fixed at $π$ in the cases of ion acoustic and ion plasma waves, respectively. In addition, a new mode with the phase lag about $π$ appears in an intermediate-frequency band between the acoustic and plasma waves.

physics.plasm-ph↗