A new method was used to reconstruct the depth profile of defects in an ion-irradiated sample by the use of slow positrons. The depth profiles of vacancy-type defects, in stainless steel which had been bombarded with 250keV Ar ions to a dose of 7.5 x 1019/m2 at room temperature, were deduced from Doppler-broadening S-parameters that were measured as a function of positron energies of up to 16keV. Without assuming any particular shape (such as Gaussian) for the defect profiles, profiling was carried out by using a least-squares fitting method. The resultant profile suggested that, in as-irradiated steel samples with lower C contents, the defect distribution peaked at a depth that was 4 times greater than that of the ion range. After annealing (1253K, 0.5h), the fitted profile showed that the peak around the average ion range was greatly enhanced. In the case of steel with 0.3wt% of added Ti, the profile exhibited almost no peak after annealing at 1073K. The results indicated that bombardment-generated vacancy clusters were more effectively stabilized by implanted Ar atoms in Ti-free steel than in Ti-added steel.

T.Aruga, S.Takamura, K.Nakata, Y.Ito: Applied Surface Science, 1995, 85, 229-38