The paper studies non‐thermal dielectric barrier discharges (DBD) operated in a parallel plate reactor (6 cm width and 16 cm long) under atmospheric pressure in Ar/HMDSO and Ar/HMDSO/O2 mixtures at different O2 to HMDSO ratio and different power. Emission spectroscopy and FT‐IR absorption spectroscopy were applied to get information on the reaction products in the DBD. The spectroscopic analysis was performed at three residence time. The properties of the polymer films deposited on silicon wafer were measured by FT‐IR absorption spectroscopy, AFM and XPS analysis. Surface tension was obtained from contact angle measurements with water and CJ2H2. The correlation between properties of plasma and the results of thin film diagnostics has been investigated.

Summary: 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.

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Measuring the second derivatives of electron retarded current characteristics of a plane probe at different angle positions, the coefficients f*i(ε) of the velocity distribution function developed as a Legendre polynomial are determined for the anisotropic plasma of a hollow cathode arc discharge. The integral values deduced from this for the electron concentration ne and the mean electron energy ε̄, as well as the drift velocity vd, show only a limited dependence on the number of angle positions used for measurement. Even for measurements at a single angle position (Druyvesteyn method), the values obtained for ne, ε̄, and vd differ by less than 10% from the corresponding values measured with the multiposition method, so long as vdrift ≤ vthermal. On the contrary, the shape of f*i(ε), like the angle dependence f*(θ)ε=const, is clearly affected by the number of angle positions used. A Maxwell distribution superimposed by a group of directed fast electrons proves to be a sufficient model for the plasma investigated here.

The role of different CFx-radicals in plasma polymerization in fluorocarbon mixtures has not been determined yet. Therefore spectroscopic investigations of dielectric barrier discharges (DBDs) in argon/fluorocarbon mixtures at atmospheric pressure were conducted with the focus on measurement of the concentration of CFx-radicals. The following diagnostic procedures were applied: FTIR absorption spectroscopy to diagnose stable compounds in the discharge, optical emission spectroscopy of the DBD in the UV and visible range and measurement of the CF2 concentration by UV absorption spectroscopy. The DBD was running in argon with the following admixtures: CF4, C2F6, C2H2F4, C3F8, C3HF7, c-C4F8. The relative concentration of the CF3-radical and the absolute concentration of CF2 in Ar/fluorocarbon mixtures were measured by emission spectroscopy and by absorption and emission spectroscopy, respectively. Emission and absorption spectroscopy were performed simultaneously in combination with electrical measurements of the discharge characteristics. The influence of small amounts of hydrogen or oxygen added to the argon/fluorocarbon mixtures was investigated.