Studies of the initial oxidation of Fe-Si alloys by AES, XPS, EELS, and LEED

Polycrystalline Fe-8.75at. % Si alloys were investigated at room temperature by various surface spectroscopies, i.e., Auger electron spectroscopy (AES) (including Ar+ depth profiling), electron energy loss spectroscopy (EELS), and x-ray induced photoelectron spectroscopy (XPS), during the initial oxidation stages under very low oxygen pressure. Experiments performed include (1) scraping to see if the surface concentration of Si on the alloy is inherently different from that of the bulk, (2) AES, EELS, and XPS monitoring during both initial oxidation of pure Fe and Fe-Si, and Ar+ or Xe+ etching back to the clean surfaces to determine the relative distribution of Si in the oxide and alloy, and (3) various comparative experiments to identify oxidation states across a thin oxide layer. Fe-6.85at. % Si (110) and (111) single crystal surfaces, and a (110) surface of pure Fe were investigated at room temperature by AES and LEED during the initial oxidation stages under very low oxygen pressures, and by Ar+ AES depth profiling the oxidized surfaces back to the clean surface. Experiments performed include (1) determination of the best annealing condition for each crystal to provide the cleanest single plane surface, (2) AES monitoring during both initial oxidation of pure Fe and Fe-Si (110), the close-packed plane of bcc crystals, and Ar+ etching back to the clean surfaces to determine the relative distribution of Si in the oxide and alloy, and (3) repetition on Fe-Si (111) to see the effects of different crystallographic orientations on the initial oxidation behavior. 126 refs., 36 figs., 6 tabs