In this study the erosion of poly(ethylene tetrafluoroethylene) (ETFE) (Tefzel) by hyperthermal atomic oxygen (AO) has been examined using X-ray photoelectron spectroscopy (XPS). Initially,
the Tefzel film had F/C and O/C atom ratios of 0.74 and 0.04, which decrease to 0.17 and 0.01, respectively,
after a 2 h exposure to a flux of 2 × 1015 atoms/(cm2 s) AO with an average kinetic energy of 5 eV. The
F/C atom ratio is further reduced to 0.02 with longer AO exposures, essentially producing a graphitic or
amorphous carbon-like layer with a carbon content greater than 90 at. %. Longer AO exposures do not
alter the composition of this layer significantly. Exposure of the AO-damaged surface to O2 or air nearly
doubles the oxygen content in the near-surface region. This is due to dissociative oxygen adsorption at
reactive sites formed at the polymer surface during AO exposure. Further exposure to AO removes this
chemisorbed oxygen. C−H bonds are important sites for attack during erosion by hyperthermal AO.
In this study, the erosion of poly(tetrafluoroethylene) TFE Teflon by hyperthermal atomic oxygen (AO) has
been examined using X-ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 1.66 decreases
to 1.15 after a 2 h exposure to a flux of 2 × 1015 atoms/cm2 s AO with an average kinetic energy ∼5 eV. The
F/C atom ratio is further reduced to a value of 0.90 after a 25 h exposure. The high-resolution XPS C 1s data
indicate that new chemical states of carbon form as the F is removed, and that the relative amounts of these
states depend on the F content of the near-surface region. The states are most likely due to C bonded only to
one F atom and C bonded only to other C atoms. Exposures of the AO-damaged surface to research-grade O2
results in chemisorption of a very small amount of O (∼0.8 at. %); this indicates that large quantities of
reactive sites are not formed during the chemical erosion by AO. Further exposure to AO removes this
chemisorbed oxygen. After exposing the AO-exposed surface to air for 90 min, O2 is chemisorbed and the
F/C atom ratio is reduced to 0.68. Another 46 h of AO exposure results in removal of this O and a further
decrease in the F/C atom ratio to 0.58.
The chemical alteration of poly(tetrafluoroethylene) Teflon by vacuum ultraviolet radiation (VUV) (115-400 nm) has been examined with X-ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 1.98 decreases to 1.65 after a 2-h exposure. The F/C atom ratio is further reduced to a steady-state value of 1.60 after a 74-h exposure. The high-resolution XPS C1s data indicate that new chemical states of carbon form as F is removed and that the relative amounts of these states depend on the F content of the near-surface region. The states are most likely due to C bonded only to one F atom, C bonded only to other C atoms, and C that has lost a pair of electrons through the emission of F Ϫ . The exposure of the VUV-damaged surface to researchgrade O 2 results in the chemisorption of a very small amount of O, and this indicates that large quantities of reactive sites are not formed during the chemical erosion by VUV. Further exposure to VUV removes this chemisorbed oxygen. A comparison of the XPS data indicates that the mechanisms of chemical alteration by VUV radiation and hyperthermal (ϳ5 eV) atomic oxygen are different, as expected, because the excitation sources are quite different.
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