The distribution of F-containing species in atmospheric nanosecond He/CF₄ plasma with downstream dielectric material

Abstract

A two dimensional self-consistent model has been established in order to investigate the distribution of F-containing species in He/CF4 APPJ and the effect of CF4 concentration on the reactive F-containing species. A portion of electron energy is consumed whenever an F is ionized from the CF4, resulting that the average densities of CF4+, CF2+ and CF+ decrease sequentially. The density of CF3+ is greater than CF4+ density due to Penning ionization of He* with CF4 and He+ + CF4 → CF3+ + F + He. In the case of He + 0.5% CF4 at 200 ns, the electron impact reactions mainly concentrate on the streamer head on the dielectric surface. The Penning ionization of He* with CF4 dominates in the region of 0 < r < 2.2 mm benefits from long-lived He* of high density and the high concentration CF4 in this region. As gas flow gradually mixes with ambient air (r > 2.2 mm), the Penning ionization of metastable He with N2 and O2 dominates in this area. As the CF4 concentration increases from 0.1% to 1%, the densities of F-containing positive ions all increase significantly. CF3, F and F2 also show the upward trend while there is little change in the spatial densities of CF2 and CF. The F-containing neutral species flux benefits from two factors: the diffusion and the conversion of positive ions. In the case of 0.1% CF4, due to the low density of CF2+, CF+ and F+ and the diffusion of F, the F flux for is consistent with CF2 and is greater than CF. However, when CF4 concentration exceeds 0.5%, the concentration of CF3+, CF2+ and CF+ are much higher than F+. The quenching of positive ions dominates on the dielectric surface in the case of 0.5% and 1% CF4, resulting that the flux of F is lower than that of CF2 and CF.

Effect of CF4 additive on dynamic surface charge deposited on dielectric by helium atmospheric pressure plasma jet

“…The mechanism of modification has not yet reached a unified understanding. To make up for the quantitative observation, numerical approaches are adopted to research the plasma-surface interaction (PSI) process between APPJ and surface under the excitation of the pulsed voltage [20,[26][27][28][29]. While obtaining the distribution of ions in a fluorocarbon plasma and giving a parametric control method, the simulation model does not adequately characterize the ions interacting with surfaces in PSI.…”

Effect of CF4 concentration on the discharge dynamics and reactive species distribution of atmospheric nanosecond pulsed He plasma jet

“…They determined the main negative ion species and ionization mechanism in the reaction process. In our previous work [43][44][45], the effect of CF 4 ratio on APPJ with downstream dielectric material was researched, the effect of small amount of CF 4 addition on He/Ar APPJ was compared, the differences between the discharge dynamics of He/Ar + CF 4 APPJ were investigated and the effect of the relative permittivity of the downstream dielectric material on plasma-surface interaction was studied. It was found that the introduction of small amount of CF 4 would enhance the jet strength of He APPJ while significantly reduce the jet strength of Ar APPJ.…”