Genta Sato

Fast Growth of Carbon Nanowalls from Pure Methane using Helicon Plasma-Enhanced Chemical Vapor Deposition

Carbon nanowalls (CNWs) are synthesized under pure methane gas (CH4) using helicon plasma-enhanced chemical vapor deposition. CH4 in the helicon discharge is effectively dissociated to hydrogen atoms and hydrocarbon radicals, resulting in the formation of CNWs on a Ni substrate only from CH4. CNWs are grown up at a high growth rate of 18 µm/h.

Effects of Ion Energy Control on Production of Nitrogen–C60 Compounds by Ion Implantation

Nitrogen–C60 compounds such as azafullerene (C59N) and nitrogen-atom-encapsulated fullerene (N@C60) are produced by implanting nitrogen ions into C60 thin films on a substrate immersed in an electron cyclotron resonance plasma under a mirror magnetic field. Each compound is found to be synthesized, depending on the ion energy provided by the potential difference between the substrate and the plasma. The optimum energy for C59N synthesis is approximately 40–50 eV, and the amount of C59N decreases in an ion energy range larger than 50 eV. In contrast, an ion energy larger than 20 eV is required for N@C60 synthesis.

Effect of cerium ions in an arc peripheral plasma on the growth of radial single-walled carbon nanotubes

Radial single-walled carbon nanotubes (radial SWCNTs) are formed by using a direct current (dc) arc discharge when carbon and metal atoms are mixed in a gas phase after the vaporization and cooled together in a liquid droplet. Since SWCNTs sprout through the precipitation of saturated carbon atoms from liquid droplets during cooling, a mass synthesis of radial SWCNTs can be achieved when a large number of liquid droplets are generated. In order to understand the effects of arc peripheral plasma parameters (electrons, ions, radical atoms, and molecules) on the growth of radial SWCNTs, the optimum production efficiency of radial SWCNTs is investigated by superimposing a radio-frequency (rf) plasma on the thermal arc plasma and controlling the arc peripheral plasma density. Two parameters—the rf power and the dc potential—of the rf electrode, which is equipped above 20 mm from the center of an arc-discharge point, are changed with the constant He pressure (200 Torr), dc arc current (75 A), and power (2000 W)...

Efficient plasma source providing pronounced density peaks in the range of very low magnetic fields

Radio-frequency discharges are performed in low magnetic fields (0–10mT) 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 a 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, bringing forth the optimization principle of plasma source design in very low magnetic fields.

Experimental Evidence of m=-1 Helicon Wave Cutoff in Plasmas

A phased multiple helical antenna selectively excites electromagnetic fields with the azimuthal mode numbers of m =+1 and -1 in a low-density plasma independently of magnetic field strength. Both the m =+1 and -1 helicon waves excited by the antenna are observed to propagate in the plasma at magnetic fields lower than 5 mT. The m =+1 helicon wave propagates even in higher magnetic fields where density peaks are not observed, but only the m =-1 helicon wave disappears. The cutoff behavior of the m =-1 helicon wave experimentally observed coincides with a theoretical expectation that this helicon wave is forbidden to propagate in a low-density region.

Investigation of Helicon-Wave Discharge in a Low Magnetic Field Using Molecular and Rare Gases

Abstract The helicon-wave discharge is performed in a low magnetic field B0 < 100 G using phased multiple helical antennas, where the phase difference among radio-frequency (RF) currents applied to each antenna is externally controlled. When an argon plasma is produced by the helical antennas, the electron density has a maximum value at B0 ~ 30 G, which is an order of magnitude larger than that at 0 G. The helicon wave with the azimuthal mode number of m = + 1 is excited at B0 yielding the density peak. In the molecular gas, such as nitrogen and oxygen, the density peaks are also observed at B0 ~ 30 G and reaches 2 × 1011 cm-3 for the RF power of 1000 W and the gas pressure of 5 × 10-2 Pa. In this case components of the plasma including ions and radicals are analyzed by an optical emission spectroscopy.

Wave Properties in a Weakly‐Magnetized Plasma Produced by Rotating Radio‐Frequency Electromagnetic Fields

Ar plasmas are produced by using spatially‐ and temporally‐rotating radio‐frequency (fRF) electromagnetic fields in very weak uniform magnetic fields. The plasma density is observed to increase greatly compared with ICP mode when the RF fields rotate in the electron‐diamagnetic direction and fce/fRF ∼ 4 is satisfied (fce: electron cyclotron frequency). Then the Trivelpiece‐Gould wave with large amplitude propagates and damps toward the downstream. The existence of the damped wave appears to contribute to the efficient plasma production.