Effect of small amount of CF4 addition on He and Ar atmospheric pressure plasma jet and influence of relative permittivity of downstream material on plasma–surface interaction.

CF₄ is an important source of fluorine groups in atmospheric pressure plasma jet (APPJ). In order to obtain reactive fluorine species under atmospheric pressure, noble gas (Ar or He) and CF₄ are usually mixed and used as the working gas of APPJ. In this paper, the differences in the discharge dynamics on He/CF₄ APPJ and Ar/CF₄ APPJ are investigated experimentally. Meanwhile, combined with simulation, the effects of downstream targets with different relative permittivity on the radial propagation range of the plasma plume and the distribution of F-containing reactive species are studied. It is discovered that the addition of a small amount of CF₄ (20 sccm) will increase the intensity of He/CF₄ APPJ due to the contribution of Penning ionization of metastable He with CF₄. Differently, the addition of CF₄ will continuously lead to a significant decrease in the intensity of Ar/CF₄ APPJ. The radial propagation range of He/CF₄ APPJ on the target surface decreases with the increase in the relative permittivity of the downstream target. The smaller relative permittivity inhibits the axial propagation speed of APPJ, but it increases the radial propagation range of reactive species. The larger relative permittivity promotes the production of F-containing reactive species and their flux intensity on the target surface. [ABSTRACT FROM AUTHOR]