Depth-selective conversion-electron Mossbauer spectroscopy (DCEMS): Effect of low-temperature Ar-ion bombardment on iron-surface layers

The surface of polycrystalline alpha-Fe-57 foils was bombarded by Ar+ ions of 5 keV energy (nominal total dose 1 x 10(17) ions/cm(2)) at 36 K and investigated in situ between 36 K and 300 K by depth-selective Fe-57 conversion-electron Mossbauer spectroscopy (DCEMS). A distribution P(B-hf) of magnetic hyperfine (hf) fields B-hf, was observed and assigned to. Ar-damaged near-surface Fe regions. At 36 K and directly after implantation, the depth-profile of the damaged Fe fraction was found to have a much higher concentration (greater than or equal to 55%) near the surface and to extend into far deeper regions (similar to 20 nm or more) than expected from the computed Ar-concentration depth profile. Compared to the values of pure undamaged alpha-Fe at 36 K the most probable hf field, B-hf(p), of the damaged Fe phase was observed to be similar to 1.3 T larger while the average isomer shift was found to be more positive by about 0.054 mm/s, indicating a smaller s-electron density al the Fe-57 nuclei in the damaged region. B-hf(p)(T) of damaged Fe is well described by a (1 - bT(3/2))-law, the spin-wave parameter b being 60% larger than for undamaged bulk alpha-Fe. Annealing of the damage occurs near similar to 200 K and above. (C) 1997 Elsevier Science B.V.