The influence of adsorbed N in the initial stages of oxidation of iron

The presence of a nitride layer on iron enhances the corrosion resistance. Thus, it is of great importance to investigate the thermochemistry of the Fe-N-O-H system. In this work, we report on the influence of adsorbed nitrogen in the surface region on the initial stages of room temperature oxidation of Fe(110). We combined ellipsometry and XPS with the high-energy ion beam technique elastic recoil detection (ERD). From the absolute coverages of N and O (and C and H) as determined with ERD and the results obtained with ellipsometry and AES, it appeared that adsorbed nitrogen (1.4 x 10(15) at cm(-2)) does not inluence the oxidation rate and the saturation oxide thickness. With XPS, also the chemical state of the iron atoms in the oxide layer is found to be unaffected, namely Fe2+ (corresponding to FeO). In addition, it followed that nitrogen remains under the oxide layer. This indicates that the nitrogen monolayer is an excellent marker for the study of mass transport across this interface. (C) 1998 Elsevier Science B.V. All rights reserved.