Foreign atom location by channeling in a helium irradiated Al-Mn alloy

Abstract

The results of channeling experiments on single crystals are not in all cases comparable to analytical calculations with the continuum model, in which the interactions with the individual atoms surrounding the channel are smoothed out. For interpretation of angular scans it is necessary to simulate the channeling process in a Monte Carlo program on the basis of the binary collision model. Such a program which yields the energy and flux distributions of the channeled ions by calculating their collisions with the nearest target atoms in the momentum approximation was described earlier. With this program, irradiation induced interstitial-impurity complexes in a dilute Al-0.09 at.% Mn alloy are analysed on the basis of 〈111〉 and 〈110〉 symmetrical and — for the first time published — asymmetrical angular scans measured by Swanson et al. Here, He + ions backscattered from the Mn atoms are assumed to be displaced in a 〈100〉, 〈110〉 or 〈111〉 direction from a normal lattice site. Displacements of this kind would occur in mixed dumbbells, where an impurity atom and a self-interstitial atom share one lattice site. The best fit to the experimental data has been obtained assuming the impurity atom to be displaced 0.14 nm in 〈100〉 direction. A 〈111〉 mixed dumbbell with a displacement of 0.22–0.27 nm might be possible, too. The evaluation needs the value of the stopping power in channel direction the knowledge of which is inaccurate. It will be shown that the results are not sensitive to the angular dependence of this stopping power.