Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) study of SF6 and SF6–CF4 plasma‐treated low‐density polyethylene films

Abstract

AbstractTime‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is used to monitor in a semi‐quantitative way the chemical modifications produced at low‐density polyethylene (LDPE) film surfaces by SF6 and SF6–CF4 plasma treatments. The influence of the plasma treatment time (SF6 plasma) and the gas composition (SF6–CF4 plasma) have been investigated. The ToF‐SIMS results are compared with plasma diagnostics (mass spectrometry and optical emission spectroscopy) and with some earlier XPS characterization.The ToF‐SIMS study of SF6 plasma‐treated LDPE films as a function of the treatment time shows two different structural developments. Beside the expected formation of CxFy structures due to the grafting of F atoms, ToF‐SIMS detects the presence of SFx species at the surface. Their high sensitivity to ablation, due to the plasma ions, was related to two possible interactions of plasma species with the LDPE surface: an adsorption of SFx+/− ions or a dissociative chemisorption of SFx neutral species. In the latter case, the low binding energy of the SC bond can explain the high sensitivity to ablation.In the case of SF6–CF4 plasma treatment, the incorporation of fluorine, as seen by ToF‐SIMS, is a function of the gas composition. Two maxima are observed when the second gas (either SF6 or CF4) is introduced at low concentration (∼10%). These maxima are confirmed by XPS and actinometric results and are explained with respect to the reciprocal influence of both gases in the plasma discharge.