The oxidation state of Fe(100) after initial oxidation in O2

Using a combination of quantitative X-ray photoelectron spectroscopy (XPS) with the high energy ion beam technique elastic recoil detection (ERD), we focus on the chemical state of thin (a few nanometers) oxide films on Fe(100). We determined quantitatively the amounts of Fe2+ and Fe3+ in the oxide layer formed at room temperature and compared these with the absolute coverages of oxygen determined with ERD. For thin oxide layers (less than or equal to 4.0 x 10(15) O atoms/cm(2) corresponding to 3 ML), the oxide layer grown on Fe(100) consists of Fe2+ mainly, indicating the growth of FeO. Some Fe-0 also seems to be present in the oxide layer. For larger coverages additional Fe atoms in the oxide are in the 3 + state, which is present mainly near the oxide/vacuum interface. Annealing of the double layer system formed or oxidizing at higher temperature leads to an increase of the relative amount of Fe2+. (C) 1999 Elsevier Science B.V. All rights reserved.