Lattice location of 15N in Fe

The lattice position of 15N atoms in crystals of Fe was studied using measurements of backscattering yields of 0.8 MeV 1H+ and alpha particle yields from the nuclear reaction 15N(p, α)12C. The 15N atoms were introduced into the Fe by three methods: (1) implantation at 35 K or 293 K with 300 keV 15N2+ to an atomic fluence of 7.5 x 1015 atoms cm-2 in a random crystallographic direction; (2) implantation under the same conditions, but in a (100) aligned direction; (3) diffusion at 770 K followed by quenching into water at 273 K. In all cases, the normalized yield of alpha particles in a channeling analysis showed a peak at (100) alignment, superimposed on a broad dip at the level Xsub(N) approx.= 0.7. The peak-to-valley ratio was P/V = 1.9 in case 2 and 2.5 in case 3. These results indicate an octahedral or near-octahedral site for the 15N atoms. This conclusion was supported by angular scans through (110) axial and [100] planar channels. The 15N atom position was quite stable with respect to irradiation by the 0.8 MeV 1H+ beam up to fluences of 1017 ions cm-2 at 35 K. Subsequent annealing up to 300 K caused only small changes in Xsub(N)sup((100)), while reduction in dechanneling of the 1H ions indicated that considerable point defect migration had taken place. During heating following implantation at 293 K, the 15N was released or diffused away from the sub-surface region in two stages, centred at 520 K and 650 K. The first is likely due to bulk diffusion of 15N, and the second is the result of release from defect traps. (orig.)