COMPOSITION DEPTH PROFILES OF PLASMA-FLUORINATED POLY(ETHYLENE-TEREPHTHALATE) FIBERS

Composition depth profiles of the outer 50 angstrom of plasma-fluorina ted poly(ethylene terephthalate) fibers were obtained by angle-depende nt X-ray photoelectron spectroscopy (XPS). The effect of sample geomet ry on XPS sampling depth and the depth distribution function (DDF) was determined theoretically for cylindrical and hemispherical surfaces. The theoretical DDFs are nonexponential. For cylindrical surfaces, the effect is small, a 22% increase in surface sensitivity. The average X PS sampling depth for smooth, properly oriented fibers is shown to var y, as it does for a planar surface, as the sine of the nominal takeoff angle. The DDF appropriate for cylindrical surfaces was incorporated into a computer program for inversion of angle-dependent XPS data to o btain composition depth profiles of the fibers. Plasma-fluorinated PET fibers were used to demonstrate the use of angle-dependent XPS on fib ers. XPS results indicate that most fluorination occurs within the top few ''monolayers,'' attack is preferentially at the phenyl ring, both -CHF- and -CF2- moieties are formed, and fluorination causes partial loss of aromaticity. (C) 1994 John Wiley & Sons, Inc.