Investigations of Fundamental Plasma Chemistry and Surface Interactions

Research seminar abstract

With increasing concern about environmental health and climate change, there is a greater need for fundamental studies investigating the 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.  Plasma assisted catalysis (PAC) provides one avenue for improving catalyst performance.  Further advancement of PAC in real-world applications like mitigation of vehicle exhaust, however, requires fundamental understanding of interactions between plasma species and comprehensive characterization of complex plasma chemistry phenomena.

In this work, inductively-coupled argon plasmas were studied to examine foundational plasma principles, specifically characterizing the role of electrons within these discharges through determination of electron temperature and density.  Subsequently, inductively-coupled NxOy plasma systems were investigated to determine relationships between precursor chemistry and gas-surface interface interactions utilizing a range of substrate materials and morphologies. Feed gas chemistry was probed via gas-phase diagnostics; time-resolved optical emission data elucidated NO(g) and N2(g) kinetics from NxOy source gases and steady-state emission and absorbance data provided information on energy partitioning between different degrees of freedom (e.g. vibrational and rotational modes).  We have determined rotational (TR) and vibrational (TV) temperatures for N2 (B3Πg ↔ C3Πu) and NO (X2Π↔ A2Σ+) and find TR and TV for both molecules show strong positive correlations with applied rf power, as well as a negative correlation with system pressure.  Notably, TV is significantly higher than TR for both N2 and NO, regardless of precursor, with TV ranging from ~2000 K to >3000 K and TR having values between ~300 K and 1000 K. 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.  Similarly, interface studies explored the influence of both non-catalytic (e.g. Si wafers) and catalytic (e.g. zeolites, Pt foil) substrates on the gas-phase chemistry in the NxOy systems. X-ray photoelectron spectroscopy and scanning electron microscopy analyses of surface oxidation and morphological changes, respectively, resulting from plasma processing will also be presented. Our holistic approach to studying the plasma, the surface, and the gas-surface interface suggests a more thorough evaluation of plasma processing for NxOy emission control.

Division(s): Physical

Speaker: Angela Hanna

Speaker Institution: Colorado State University

Event Date: 02-28-2018

Event Time: 4:00 PM

Event Location: Chemistry A101

Mixer Time: 3:45 PM

Mixer Location: Chemistry B101E

Host: E. Fisher