Effect of VUV radiation and reactive hydrogen atoms on depletion of fluorine from polytetrafluoroethylene surface

Modification of polytetrafluoroethylene (PTFE) surface upon treatment with reactive species from hydrogen plasma (ions, neutral atoms, and UV/VUV) as well as synergistic effects are presented and explained. PTFE samples were either directly exposed to hydrogen plasma or separately to UV/VUV radiation or atomic hydrogen, and the resulting evolution of the surface composition was determined by X-ray photoelectron spectroscopy. High-density plasma was created by an inductively-coupled radiofrequency discharge in the H-mode. Samples placed in specially designed holders were covered with various optical windows (magnesium fluoride, quartz glass, or borosilicate glass), to allow for separate treatments with either VUV, UV or visible radiation. Rapid fluorine depletion was observed either at a direct exposure to plasma or to VUV; however, the best results were observed at a combined treatment with VUV/UV and atomic hydrogen. For direct treatment, a minimum in the F/C ratio was observed at the shortest time of 1 s. The F/C dropped from 2.2 to 0.4, whereas at longer times it increased to 1. For treatment with UV/VUV and for the combined treatment with UV/VUV and atoms, the F/C decreased with treatment time and stabilized at 0.6 and 0.4, respectively. Exposure to the afterglow did not result in significant modification.