Effect of gas impurities on the operation of dielectric barrier discharges fed with He, Ar, and Ar-C3F6

Abstract

The influence of N2, O2, air, and water vapor feed gas impurities on the operation of an atmospheric pressure parallel plate DBD fed with helium and argon was investigated. The addition of increasing amounts of these impurities, under fixed excitation frequency and applied voltage, is responsible above certain thresholds of two distinct phenomena, namely the transition from a homogeneous to a filamentary appearance of the discharge and the contraction of the discharge volume. Among the different contaminants N 2 shows the highest threshold limit values, O2 and H 2O the lowest ones, while air generally exhibits an intermediate behavior. The effect of feed gas impurities was also studied on the PE-CVD of fluoropolymers from Ar-C3F6 fed filamentary DBDs. Contaminants addition results in a decrease of the input power and of the deposition rate as well as in a change of the film morphology, however it does not influence significantly the chemical composition of the fluoropolymer film, the monomer depletion and the distribution of by-products in the exhaust gas. In this work known concentrations of contaminants (i.e., N2, O 2, air, and H2O) were added to He and Ar fed DBDs in order to assess the discharge regime and overall stability. The deposition of fluoropolymers from Ar-C3F6 FDBDs was also investigated as a function of the feed impurity level. Contaminants addition results in a decrease of the deposition rate and in a change of the film morphology, however it does not influence significantly the chemical composition of the coating. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.