Impact of catalytic surfaces on atmospheric RF plasma dynamics

Abstract The combination of plasma and catalysis allows flexible solutions for species conversion. Any plasma catalysis synergism can constitute either of plasma conversion enhanced by a surface process or a surface process enhanced by plasma-excited species as reaction partners. The first case of the impact of a catalytic surface on plasma dynamics is investigated using phase-resolved optical emission spectroscopy (PROES) in RF helium and argon discharges with nitrogen, hydrogen, and oxygen admixtures. Different surfaces are being employed, and the electron energetics are monitored by measuring the temporal and spatial development of the helium emission line. Surfaces with high secondary electron emission coefficients (SEEC or γ e ) lead to increased electron densities in front of the surface, thereby enhancing plasma conversion. Higher SEEC promotes the transition of the discharge from α -mode to γ -mode, but the emission strength is also governed by electron energy distribution, surface charge dynamics, and surface roughness. The γ e values for a specific material from the former literature cannot necessary directly used, because the SEEC depends also on the microstructure of the surface, which may vary. Consequently, the PROES measurements presented here provide realistic γ e values, which better reflects the performance of the catalytic coating under actual discharge conditions, and show the impact on discharge dynamics.