DETERMINATION OF PHOTOELECTRON ATTENUATION LENGTHS IN THIN OXIDE-FILMS ON IRON SURFACES USING QUANTITATIVE XPS AND ELASTIC RECOIL DETECTION

Thin oxide films play an important role in the corrosion of metals. Us ing XPS it is possible in principle to obtain information on the chemi cal state of near-surface atoms, the stoichiometry of the surface laye r and its thickness. A problem is the quantification of XPS spectra, d ue to the large uncertainty in the value of both electron attenuation lengths as well as sensitivity factors. By applying the Tougaard backg round subtraction method and comparing only peak intensities of the Fe 2p and O 1s peaks with those of Fe, FeO and Fe2O3 reference samples, we determined the stoichiometry of the oxide layer grown on Fe(100) an d Fe(110) at 200 degrees C and room temperature to be Fe0.90 +/- 0.05O . We combined XPS with the high-energy ion-beam technique of elastic r ecoil detection (ERD). By comparing the absolute coverages of oxygen d etermined by ERD with the intensities of different XPS peaks, we were able to determine the attenuation lengths for kinetic energies of 776 eV (Fe 2p) and 957 eV (O Is) to be 93 x 10(15) and 9.9 x 10(15) Fe0.9O molecules cm(-2), respectively. (C) 1998 John Wiley & Sons, Ltd.