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17 Sep 2007

Volume 91, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 91, 123101 (2007); http://dx.doi.org/10.1063/1.2784389 (3 pages)

Thierry Laroche, Alexandre Vial, and Matthieu Roussey
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Multibubble plasma production and solvent decomposition in water by slot-excited microwave discharge

T. Ishijima, H. Hotta, H. Sugai, and M. Sato

Appl. Phys. Lett. 91, 121501 (2007); http://dx.doi.org/10.1063/1.2783209 (3 pages) | Cited 20 times

Online Publication Date: 17 September 2007

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Intense microwaves are injected from a slot antenna into water partly filling a metal vessel. When the vessel is evacuated to saturated vapor pressure ( ∼ 5×103 Pa) of water, microwave breakdown gives rise to plasmas in many bubbles in the boiling water. Gas bubbling technique enables production of multibubble plasmas in water even at atmospheric pressure. Optical emissions from the exited species are investigated to identify radical species in water. In order to demonstrate application to purification of polluted water, methylene blue and trichlorethylene solution in 8 l water were observed to rapidly decrease with multibubble plasma treatment.
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52.50.-b Plasma production and heating
52.80.Pi High-frequency and RF discharges

Direct measurements of neutral density depletion by two-photon absorption laser-induced fluorescence spectroscopy

A. Aanesland, L. Liard, G. Leray, J. Jolly, and P. Chabert

Appl. Phys. Lett. 91, 121502 (2007); http://dx.doi.org/10.1063/1.2786601 (3 pages) | Cited 18 times

Online Publication Date: 19 September 2007

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The ground state density of xenon atoms has been measured by spatially resolved laser-induced fluorescence spectroscopy with two-photon excitation in the diffusion chamber of a magnetized Helicon plasma. This technique allows the authors to directly measure the relative variations of the xenon atom density without any assumptions. A significant neutral gas density depletion was measured in the core of the magnetized plasma, in agreement with previous theoretical and experimental works. It was also found that the neutral gas density was depleted near the radial walls.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Xz Magnetized plasmas
52.25.Ya Neutrals in plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Hf Plasma-material interactions; boundary layer effects

Microplasma synthesis of metal nanoparticles for gas-phase studies of catalyzed carbon nanotube growth

Wei-Hung Chiang and R. Mohan Sankaran

Appl. Phys. Lett. 91, 121503 (2007); http://dx.doi.org/10.1063/1.2786835 (3 pages) | Cited 24 times

Online Publication Date: 20 September 2007

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Catalytic properties of metal nanoparticles toward gas-phase carbon nanotube (CNT) growth are presented. Narrow dispersions of iron (Fe) and nickel (Ni) nanoparticles are prepared in a direct current microplasma reactor and subsequently introduced with acetylene (C2H2) and hydrogen (H2) into a heated flow furnace to catalyze CNT growth. Aerosol size classification and high-resolution transmission electron microscopy show that CNT growth occurs on Ni particles at lower temperatures than that for similarly produced Fe nanoparticles. Activation energies of 117 and 73 kJ/mol are found for Fe and Ni catalyst particles, respectively, suggesting that CNT growth occurs by carbon surface diffusion.
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81.16.Hc Catalytic methods
61.46.Fg Nanotubes
81.07.De Nanotubes
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Displacement current and surface flashover

J. R. Harris, G. J. Caporaso, D. Blackfield, and Y.-J. Chen

Appl. Phys. Lett. 91, 121504 (2007); http://dx.doi.org/10.1063/1.2785116 (3 pages) | Cited 3 times

Online Publication Date: 21 September 2007

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High-voltage vacuum insulator failure is generally due to surface flashover rather than insulator bulk breakdown. Vacuum surface flashover is widely believed to be initiated by a secondary electron emission avalanche along the vacuum-insulator interface. This process requires a physical mechanism to cause secondary electrons emitted from the insulator surface to return to that surface. Here, it is shown that when an insulator is subjected to a fast high-voltage pulse, the magnetic field due to displacement current through the insulator can provide this mechanism. This indicates the importance of the voltage pulse shape, especially the rise time, in the flashover initiation process.
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52.80.Vp Discharge in vacuum
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