A computer simulation of slow-positron implantation depths in aluminum

The mean penetration depths and stopping profiles of positrons with incident energies up to 10 keV impinging on semi-infinite aluminum with normal and oblique angles of incidence are stochastically modelled within a Monte-Carlo framework. The elastic scattering cross sections have been obtained from a partial wave expansion. To model inelastic core and valence electron excitation, we have used the Gryzinski's expression. Our simulated results agree very well with the available experimental data and clearly demonstrate that the mean penetration depths are not adequately described by the simple power law commonly used in defect profiling. This suggests that both mean penetration depths and stopping profiles cannot generally be modelled by material-independent parameters as was proposed previously. The mean penetration 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 width of the implantation profiles.