Symmetric self-organized discharge filaments have been observed in the rf ͑500 kHz͒ dielectric barrier discharge of Ar gas between two parallel quartz plates with a MgO film. The arrangement of the filaments is confined around the center on the quartz plate plane. With increasing voltage, the number of filaments increases, and the area of filament arrangement also increases. The arrangement of the filaments does not move if the quartz plate with a MgO film is employed, while the whole arrangement rotates without a MgO film. According to the results of current-voltage measurements, Lorentz attractive force is much smaller than Coulomb repulsive force. This suggests that a confinement potential exists as in the case of two-dimensional Coulomb systems in a parabolic potential. However, some of the filament arrangements do not match to those for charged particles in the Coulomb systems, which suggests that the confinement potential does not have pure parabolic profile.
Conductive diamond whiskers were fabricated by maskless oxygen plasma etching on highly boron-doped diamond substrates. The effects of the etching conditions and the boron concentration in diamond on the whisker morphology and overall substrate coverage were investigated. High boron-doping levels (greater than 8.4 × 10(20) cm(-3)) are crucial for the formation of the nanosized, densely packed whiskers with diameter of ca. 20 nm, length of ca. 200 nm, and density of ca. 3.8 × 10(10) cm(-2) under optimal oxygen plasma etching conditions (10 min at a chamber pressure of 20 Pa). Confocal Raman mapping and scanning electron microscopy illustrate that the boron distribution in the diamond surface region is consistent with the distribution of whisker sites. The boron dopant atoms in the diamond appear to lead to the initial fine column formation. This simple method could provide a facile, cost-effective means for the preparation of conductive nanostructured diamond materials for electrochemical applications as well as electron emission devices.
Atmospheric pressure discharges in Ne, N2 and N2/O2 gases have been investigated with a novel high-voltage pulse power supply. Three characteristic types of discharge modes were observed: (1) diffuse glow discharge seen in Ne gas both with the eye and high-speed camera; (2) diffuse glow-like discharge in N2 gas observed with the eye, but seen as a vague filamentary discharge with a high-speed camera; and (3) clear filamentary discharge in N2/O2 gas mixture both with the eye and high-speed camera. Characteristics in the current and voltage waveforms revealed that the existence of the second voltage with opposite polarity following the first impulse voltage was important to have a diffuse glow-like discharge. This suggests that elimination of the memory effect by non-uniformly distributed charges on the surface is important for obtaining the diffuse mode because the non-uniformity triggers a positive feedback to the current constriction at the points with higher charge density, and results in filamentation of the discharge.
Solution plasma processing (SPP) has been performed on multiwalled carbon nanotubes (MWCNTs) in ammonia aqueous solution. The MWCNTs, which do not disperse in aqueous solution, uniformly dispersed after the SPP. Only 2 h was required to obtain 10 g of the dispersed MWCNTs, while 7 days and additional chemicals were required for 185 mg in a previous study. The X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy of the SPP-treated MWCNTs revealed that nitrogen- and oxygen-containing groups are formed on the MWCNTs. Serious damage to the MWCNT structure was not observed in the Raman spectrum or transmission electron microscopy images of the SPP-treated MWCNTs. The composite materials prepared using polyamide 6 with the SPP-treated MWCNTs showed better tensile, bending, and impact strength than those prepared with nontreated MWCNTs.
Plasma copolymerization of hexamethyldisiloxane
(HMDSO, (CH3)3-Si-O-Si-(CH3)3) and
tetrafluoroethylene (CF2=CF2) was performed
using an RF plasma enhanced chemical vapor deposition method,
for its application to low dielectric constant intermetal dielectrics.
Film structure was investigated by X-ray photoelectron
spectroscopy and Fourier transform infrared (FT-IR) spectroscopy.
Film composition was controlled gradually from that of fluorinated
carbon to organic siloxane by changing the HMDSO mixing ratio.
The films possessed a dielectric constant of less than 2.5
for an HMDSO mixing ratio of less than 10%.
Thermal treatment of the films revealed that the C-F
n
, Si-O-Si,
Si-(CH3)
n
and Si-(CH2)
n
-Si bonds were stable to
400°C, but the C-H2 bonds were not. In situ gas-phase
FT-IR spectroscopy was also performed on the plasma, and the reaction
mechanisms are discussed.
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