Plasma Induced by a Carbon Nanotube (CNT) Generated Electron Beam

Abstract

A device using an energetic electron beam from a carbonnanotube electron emitter was developed to generate an atmospheric pressure plasma. The low-pressure electron source region $( 10 ^{-6}$ mbar) and the higher pressure (up to 1 atm) plasma generation region were separated by a 300 nm SiN x window/membrane. The energy of the electron beam was of the order of 10 kV with a current of 10 μA prior to passing through the window with nearly 85% of the beam passing through the window to the plasma generation region with a 10% loss in energy. The device could be operated in one of two modes, closed or opened. Closed mode operation was used to generate excimer emissions from XeI* and XeCl* at 253 nm and 308nm, respectively, at pressures below atmospheric. Open mode operation was with ambient air and with a gas flow of Ar or He across the SiN x window. Optical emission spectroscopy revealed that the open mode operation yielded a variation of excited state species that was found to be dependent on the electron beam energy and the neutral gas flow in the reaction region. Identified in the spectra were the N 2 Second Positive System and the First Negative System, along with OH emission at 310 nm. The emission from the OH radical at 310 nm was found only with an Argon gas flow, whereas, the Helium flow produced an $\mathrm {{N}_{2}}^{+}$ emission at 391 nm. The excimer emission, produced in the closed mode operation, was also observed using optical emission spectroscopy. The Xenon pressure was varied between 100 and 500 Torr inside the closed reaction cell in which iodine crystals with a vapor pressure, at room temperature, of 0.2 Torr were placed. The maximum intensity of the excimer emission at 253 nm occurred at a pressure of 150 Torr. Production of the XeCl* excimer was facilitated by placing a chloride compound in the closed gas cell. Coatings with multilayers of Aluminum/Aluminum Oxide were necessary to protect the SiN x window from reactive etching produced by the halogen species. The closed system was also studied with N 2 gas where the resulting spectrum was dominated by the Second Positive System between 300 to 425 nm with the 0–0 transition at 337 nm as the most intense feature.