Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: I. Flat surfaces

In atmospheric pressure discharges, ion energies are typically thought to be thermal with values dominantly <1 eV. In the heads of filaments in dielectric barrier discharges (DBDs), electric fields can exceed 200 kV cm−1 when the filament is far from a surface. As the filament approaches and intersects a dielectric surface, much of the applied potential is compressed into the voltage drop across the head of the filament due to the high conductivity of the trailing plasma channel. When the filament strikes the surface, this voltage is transferred to the resulting sheath and into the material of the surface. The degree of electric field compression depends on the dielectric constant ε/ε0 of the surface. Upon intersection of the filament with the surface, the electric fields in the resulting sheath can exceed 400–800 kV cm−1, with larger values corresponding to larger ε/ε0. When accelerated in these fields, ions can gain energies across their mean free path (0.5–1μm) up to 20 eV for dielectrics with low ε/ε0 and up to 150 eV for dielectrics with high ε/ε0, albeit only for the duration of the intersection of the streamer with the surface of a few ns. In this paper we report on results from a computational investigation of the ion energy and angular distributions (IEADs) incident on dielectric flat surfaces resulting from the intersection of DBD filaments sustained in atmospheric pressure air. We describe the transient and spatially dependent IEADs as the filament spreads across the polymer. (Some figures in this article are in colour only in the electronic version)