REEMITTED POSITRON SPECTROSCOPY OF NEAR-SURFACE DEFECTS

Simulations of the energy spectra of positrons reemitted from aluminum that contains subsurface defects are presented. The defects are vacancies and divacancies that have positron trapping rates which depend strongly on energy in the 1-eV energy range due to low-lying positron p-wave scattering resonances. Because of this, the energy spectra are depleted in the eV energy range when the defects are present. There is also depletion in this energy range with increasing sample temperature because the increased positron-phonon scattering at the higher temperatures impedes the motion of the positrons back to the surface. The simulations use a diffusion model of the positron energy-loss and scattering processes. The results are compared with the experimental data of Nielsen, Lynn, and Chen [Phys. Rev. Lett. 57, 1789 (1986)]. © 1990 The American Physical Society.