Surface and bulk compositional characterization of plasma‐polymerized fluorocarbons prepared from hexafluoroethane and acetylene or butadiene reactant gases

The surface tension and surface and bulk composition of plasma-polymerized fluorocarbon films (PPFCs) prepared from hexafluoroethane (HFE) and either acetylene or butadiene reactant gases were determined. Increasing the HFE reactant gas content from 0 to 100% gave an increase in the amount of fluorine incorporated in the films and a shift to incorporation of more highly fluorinated species at the film surface, according to X-ray photoelectron spectroscopy (XPS ) data. Hydrogen levels in the films were determined by forward recoil spectrometry (FRS) and were shown to be inversely dependent on HFE concentration in the reactant gas feed and dependent on hydrocarbon co-reactant type. The compositional changes were mirrored by changes in the surface tension from 52 to 20 mN/m. XPS and surface tension results demonstrated that fluorine incorporation at the surface of the PPFCs is significantly reduced when butadiene, rather than acetylene, is used as a co-reactant gas with HFE. The differences are attributed to higher concentrations of hydrogen, which acts as a scavenger for reactive fluorine atoms and as an inhibitor in the CF x → CF x+1 reaction, and of carbon, decreasing the F/C ratio, when butadiene is used as the hydrocarbon source. Furthermore, potential changes in surface composition due to energetic ion bombardment are discussed. Three factors were suggested as strongly influencing the composition and the properties of the PPFCs: 1) the energy input into the plasma polymerization reaction, 2) the amount and type of fluorine scavenging reagent introduced with the HFE, and 3) the elemental composition of the reactant gases.