Determination of the Electron Escape Depth for NEXAFS Spectroscopy
Daniel A. Fischer, K E. Sohn, M D. Dimitriou, Jan Genzer, C Hawker, E. J. Kramer
Depth profiling using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to determine the carbon atom density as a function of depth by analyzing the post-edge signal in NEXAFS spectra. We show that the common assumption in the analysis of NEXAFS data from polymer films, namely, that the carbon atom density is constant as a function of depth is not valid. This analysis method is then used to calculate the electron escape depth (EED) for NEXAFS in a model bilayer system that contains a perfluorinated polyether (PFPE) on top of a highly oriented pyrolitic graphite (HOPG) sample. Because the carbon atom densitites of both layers are known, in addition to the PFPE surface layer thickness, the EED is determined to be 1.95nm. This EED is then used to measure the thickness of the perfluorinated surface layer of a poly(4-(1H, 1H, 2H, 2H-perfluorodecyl) oxymethylstyrene) (PFPS).