Etching of plasma-polymerized tetrafluoroethylene, polytetrafluoroethylene, and sputtered polytetrafluoroethylene induced by atomic oxygen [O(³P)]^†

A study was carried out of the surface recession (etching) of thin films of plasma-polymerized tetrafluoroethylene (PPTFE), polytetrafluoroethylene (PTFE), and ion-beam sputter-deposited polytetrafluoroethylene (SPTFE), exposed to atomic oxygen [O(³P)] downstream from a nonequilibrium radio-frequency O₂ plasma. At 22°C, the etch rates for PTFE, SPTFE, and PPTFE were in the ratio of 8.7 : 1.0. A thin, conformal coating of PPTFE (etch rate of 0.3 nm/h at 22°C) was found to protect an underlying, cast film of a reactive polymer, cis-1,4-polybutadiene (etch rate of 0.13 mg/cm² h ≡ 1300 nm/h at 22°C), against O(³P) attack for the time required to fully etch away the PPTFE coating. From ESCA analysis, PTFE exhibited only minor surface oxidation (uptake of 0.5 atom % O) upon etching, its F/C ratio decreasing slightly from 2.00 to 1.97; PPTFE exhibited considerable surface oxidation (uptake of 5.9 atom % O) and a decrease in F/C ratio from 1.30 to 1.23; and SPTFE exhibited a surface oxidation (uptake of 2.2 atom % O) intermediate between those of PTFE and PPTFE, with a decrease in F/C ratio from 1.73 to 1.67. The O(³P)-induced etching of PTFE had an activation energy of 3.8 Kcal/mol, but no activation energy value was obtained for PPTFE which gave a nonlinear Arrhenius plot apparently because of thermally induced thinning above 50°C.