Implantation profiles and depth distribution of slow positron beam simulated by Geant4 toolkit

The positron implantation profiles and depth distribution in metal, semiconductor, and polymer surfaces are simulated using the Monte-Carlo-method-based Geant4 toolkit. As per the slow positron beam technique, the monoenergetic positron beams (in the range from 1 to 35 keV) with 1.5 mm radius is injected into semi-infinite samples in the present work. The implantation profile of 3.1 keV positrons in Fe is in good agreement with the Makhovian profile. The mean depth and depth resolution exhibit a general negative correlation with the material densities and incident position energy, respectively, while the fixed peak energy of backscattered positrons exhibits a net correlation with atomic number Z. Furthermore, the implantation profiles present better z-axis resolution with increasing incident angle, and this effect is more prominent for low-density materials. The results can provide theoretical support for new measurement methods based on the slow positron beam technique, such as segment measurements and micro-beam scanning measurements.