BEHAVIOR OF NITROGEN-IMPLANTED INTO ZR AT HIGH FLUENCE

In order to evaluate the depth profiles of ions implanted at high fluence, the behavior of nitrogen implanted into Zr samples was studied in detail by nuclear reaction analysis using the N-15(p, alphagamma)C-12 reaction at E(p) = 429 keV. Zr samples were implanted with N-15 ions of 50 keV to a total fluence of 10 X 10(17) ions/cm2 at room temperature and 500-degrees-C. It was found that the nitrogen concentration exceeded 50% on both sides of the mean projected range (R(p)) for a fluence of 7 x 10(17) ions/cm2. The layers of over-stoichiometry were removed by subsequent ion implantation and then a trapezoidal profile was obtained for a fluence 10 x 10(17) ions/cm2. Moreover N-14 and N-15 implantations were superimposed on Zr samples in order to measure the atomic migration of pre-implanted N-15 caused by the subsequent N-14 implantation. It was found that nitrogen atoms near R(p) moved to both sides of R(p) by the collision cascade and the peak of the depth profile of N-15 split into two peaks with increasing N-14 ion fluence. These experimental results on the depth profile were compared with the theoretical results obtained by Monte Carlo simulation of the dynamic SASAMAL code, in which excess atoms over stoichiometry are assumed to diffuse depending on the degree of the radiation damage. Good agreement with theoretical results was obtained.