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-. The exposure of the VUV-damaged surface to research-grade 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 (similar to5 eV) atomic oxygen are different, as expected, because the excitation sources are quite different. (C) 2004 Wiley Periodicals, Inc.