A computer simulation of slow-positron implantation depths in aluminum

The mean penetration depths and stopping profiles of positrons with inciden t energies up to 10 keV impinging on semi-infinite aluminum with normal and oblique angles of incidence are stochastically modelled within a Monte-Car lo framework. The elastic scattering cross sections have been obtained from a partial wave expansion. To model inelastic core and valence electron exc itation, we have used the Gryzinski's expression. Our simulated results agr ee very well with the available experimental data and clearly demonstrate t hat the mean penetration depths are not adequately described by the simple power law commonly used in defect profiling. This suggests that both mean p enetration depths and stopping profiles cannot generally be modelled by mat erial-independent parameters as was proposed previously. The mean penetrati on depth decreases non-monotonically with increasing the angle of incidence from 0 degrees to 80 degrees. This can be seen from the reduction of the w idth of the implantation profiles.