The membrane properties of a Nafion surface can be modified by ion implantation with N+ or F+. The results are presented of an X-ray photoelectron spectroscopy (XPS) study of implanted surfaces. For the interpretation of the XPS spectra, calculations using a semiempirical quantum chemical formalism (AM1) have been applied, in conjunction with a charge-potential model, to predict the C,, cote electron binding energies. (C) 2003 Wiley Periodicals, Inc.