Investigations of fundamental nitrogen oxide plasma chemistry & surface interactions

With increasing concern about environmental health and climate change, there is a greater need to investigate fundamental reactivity of pollutant species. Improving the effectiveness of substrates used in vehicular emissions abatement hinges on the ability to discern the contributions of gas-phase species in surface reactions. A fundamental understanding of interactions between plasma species is essential to characterizing complex plasma chemistry phenomena. Inductively-coupled NxO
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plasma systems were investigated to determine relationships between precursor chemistry and gas-surface interface reactions with different substrates. Precursor chemistry was probed via gas-phase diagnostics; time-resolved optical emission data elucidated NO(g) and N2(g) production kinetics from NxO
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source gases, whereas steady-state emission and absorbance data provide information on energy partitioning between different degrees of freedom (e.g. vibrational and rotational modes).
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We have also explored the role of electrons within these discharges through the analysis of Ar emission lines. Ultimately, these data afford significant insight into understanding of molecule formation and decomposition pathways, as well as overall plasma chemistry in nitrogen and oxygen containing plasma systems of interest to pollution abatement. Additionally, these gas phase studies were performed in the presence of flat, micro- and nanostructured materials. Specifically, interface studies explored the influence of both non-catalytic (e.g. Si wafers, glass slides) and catalytic (e.g., Pt foil, Au films, zeolites) substrates on both the kinetics and energetics within various NxO
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discharges. Optical spectroscopies were employed to measure the relative gas phase density of NO, N2, and OH as a function of plasma operating parameters (i.e. applied rf power, gas mixture, substrate architecture). X-ray photoelectron spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy were utilized to assess surface chemistry, substrate morphology, and bulk characteristics of the material, respectively, before and after plasma exposure. Our holistic approach to studying the plasma, the surface, and the gas-surface interface suggests a more thorough evaluation of plasma processing for NxO
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emission control.