DESIGN, IMPLEMENTATION, AND APPLICATIONS OF DEVICES FOR GENERATION OF ULTRA HIGH FREQUENCY MINIATURE PLASMAS
Open AccessThe main objectives of this research are: 1) to develop novel and application-specific sources for generation of ultra-high frequency miniature plasmas that operate in a wide pressure range (~1 to 760 Torr) with power requirement of less than 10 W, 2) to investigate the active species of such miniature plasma sources using mass spectrometry and optical emission spectroscopy, and 3) to explore novel applications of such miniature plasma sources with an emphasis on their application in chemical analysis for identification of gaseous species and volatile organic compounds. First, a miniature inductively coupled plasma (ICP) sources was developed, operating at a pressure of 1 to 10 Torr and a power requirement of 2 - 8 W with carbon dioxide, helium and argon as the plasma gas. The plasma impedance was measured using Smith chart. Furthermore, the background emission of the miniature ICP sources was monitored to investigate the species in the carbon dioxide, argon, and helium miniature ICPs. Ethylene, neon, and hydrogen were introduced separately into the miniature carbon dioxide ICP for qualitative identification. Distinguishable peaks were observed at approximately 431, 585, and 656 nm for ethylene, neon, and hydrogen, respectively. Second, a miniature ICP operating under conditions mimicking the Martian atmosphere was investigated. The miniature ICP source was able to generate a stable plasma, operating at a pressure range of 4 to 16 Torr and a power requirement of less than 3.5 W. The quantitative analysis of trace amounts of methane sample was performed by interfacing the miniature ICP with a quadrupole mass spectrometer. The effects of pressure, plasma power, and skimmer voltage were investigated and optimized for obtaining analytical results. Excellent calibration curves were obtained for CH3+ at m/z of 15. A detection limit of 0.15 ppm for CH3+ at 16 Torr was achieved using a quadrupole mass spectrometer. In addition, a magnetic loop antenna was used to produce an atmospheric pressure micro plasma at ultrahigh frequencies for operation in air. Pulse modulation of the input signal resulted in reduced power consumption for igniting and sustaining the plasma. The nature of excited species in the plasma was not altered due to pulse modulation. Furthermore, an atmospheric-pressure argon plasma jet was produced using the magnetic loop. Fast photography revealed that the plasma jet was formed by a fast moving U-shaped plasma arc. To explore the effects of plasma on biofilms, an epidermal onion membrane was treated by the plasma jet. After treatment, the shape and the hydrophobicity of the membrane were altered. The optical emission spectroscopy of the plasma jet was used to study the dominant species that interact with the surface under treatment. Subsequently, the developed plasma jet was used as ambient ionization for mass spectrometry of volatile organic compounds. It is demonstrated that the developed plasma jet is an effective source for ambient ionization of volatile organic compounds.
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Taghioskoui_gwu_0075A_11198.pdf | 2018-01-16 | Open Access |
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