Spectroscopic Diagnostics of DBD in Ar/Fluorocarbon Mixtures – Correlation between Plasma Parameters and Properties of Deposited Polymer Films

Abstract

AbstractSummary: Spectroscopic diagnostics of a pulse‐modulated dielectric barrier discharge (DBD) in fluorocarbon mixtures at atmospheric pressure are reported. Plasma diagnostics was performed by FTIR‐absorption spectroscopy as well as by emission/absorption spectroscopy in the UV‐vis range. The following fluorocarbon molecules have been studied: CF4, C2F6, C3F8, C2H2F4, C3HF7 and c‐C4F8. Emission and absorption spectroscopy were performed simultaneously in combination with the measurement of the electric parameters (current, voltage and phase). Surface tension measurement, FTIR‐absorption spectroscopy and XPS were applied to get information on the surface tension, chemical composition and structure of the fluorocarbon polymer films in dependence on the fluorocarbon gas applied. Substrates used were Si wafers, foils and textiles. Analysis of XPS spectra indicates that polymer films can be deposited if the F/C ratio of precursor molecule is smaller than or close to 3. FTIR‐absorption spectra of the films on Si wafers indicated an “amorphous” film structure with the main absorption peak of CF2‐groups at 1 200 cm−1. F/C ratio of precursor molecule is strongly correlated with the appearance of an “amorphous” PTFE absorption peak at 740 cm−1 in the discharge volume. XPS‐analysis and FTIR‐absorption spectroscopy show the influence of H atom content in fluorocarbon molecule or admixture of H2 molecules on the cross linking effect in the films. Depending on the experimental conditions and gas mixture, films with a smallest surface tension of about 11 mN/m could be deposited.Dependence of surface tension (total, polar and dispersive components) on effective deposition time and substrate material (PP, PET) (Ar/c‐C4F8 discharge).magnified imageDependence of surface tension (total, polar and dispersive components) on effective deposition time and substrate material (PP, PET) (Ar/c‐C4F8 discharge).