ARXPS study of a plasma-treated polymer surface: An example of Case II diffusion?

The Laplace transform of the Wang, Kwei and Frisch equation for the concentration depth profile of a diffusant in a glassy polymer has been derived and applied to the interpretation of ARXPS data obtained on a polystyrene film exposed to a helium/oxygen plasma. It was found that the best fit to the data was given by a rectangular oxygen profile that would be characteristic of Case II diffusion. The reliability of this finding is discussed in terms of the uniqueness of the fitted profile.