The Microionizer - A Solid State Ion Source for High Pressure Mass Spectrometry Public Deposited

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Last Modified
  • March 20, 2019
Creator
  • Cavanaugh, Craig
    • Affiliation: College of Arts and Sciences, Department of Applied Physical Sciences, Materials Science Graduate Program
Abstract
  • This work describes the development of a novel, microfabricated solid-state ionization source (a “microionizer”) for use with high pressure mass spectrometry (HPMS). HPMS is intended for miniature, low-cost, portable instrumentation. As such, the microionizer is designed as a small, low-power ion source compatible with the 1 Torr air environment of HPMS. The microionizer is a field effect device based upon silicon-on-insulator technology that functions as a dual-source, producing field emission for internal electron impact ionization (EI) and external field ionization. External ion injection into the miniature cylindrical ion trap (mCIT) was performed in helium, nitrogen, or air buffer gases at 1 Torr using traditional ion sources (thermionic emitter and glow discharge) for proof-of-concept experiments. Further studies in helium and air examined the effects of pressure, ion kinetic energy, and ion trap potential well depth changes with drive radiofrequency (RF) signal frequency and amplitude. Results indicated that mass spectral signal intensity can be maximized at pressures ranging from 10 to 1000 mTorr by tuning ion kinetic energy between 20 to 250 eV and increasing potential well depth aids external ion injection. Nine generations of microionizers were fabricated to optimize microionizer performance. The first generation microionizer was coupled with HPMS as a field emission source and generated helium and air-based high pressure mass spectra. However, high current draw limited the microionizer lifetime and prevented field strengths necessary for field ionization. Generations two through nine encompassed processing variations of device fabrication procedures, development of robust electrical contacts, and microionizer device incorporation into the ion trap electrode stack, leading to improved microionizer signal intensity and low power (< 1 mW average power) consumption. The ninth generation microionizer demonstrated operation as both a field emission and field ionization source in air buffer gas at 1 Torr. Electric field strengths for field emission were near 1 MV/cm, while field ionization required greater than 1.8 MV/cm. The microionizer generated mass spectra of volatile organic compounds (such as benzene and dimethylaniline) in both modes and lifetime was found to be 9 h for field emission and 490 h for field ionization under continuous mass spectral acquisition.
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Rights statement
  • In Copyright
Advisor
  • Falvo, Michael
  • Washburn, Sean
  • Warren, Scott
  • Glish, Gary
  • Ramsey, J. Michael
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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