Comparative study of secondary electron emission from solids under positron and electron impacts

Secondary electron emission from gold caused by the impacts of positrons and electrons at keV or less energy is investigated by means of a Monte Carlo simulation of elastic and inelastic collision processes of the projectiles and cascade electrons inside the solid. The cross-section for the elastic collision of each particle with an atom in the solid is calculated using the partial wave expansion technique, whereas the cross-section for the inelastic collision or for the electron excitation is calculated from the Ashley's optical-data model. Because of less large-angle elastic scattering of the positron, the calculated backscattering coefficient is smaller for the positron than the electron. At low impact energies (<600 eV), however, the calculated secondary electron yield for the positron is larger than that for the electron, due to the larger inelastic energy loss of the positron and the larger number of excited electrons. The difference between the distributions for the positron and the electron calculated at such low impact energy is due to increasing emission of high-energy electrons excited by the projectile without the cascade process; which is more enhanced for the electrons than the positrons. These calculated results are consistent with the recent findings based on experiments. (C) 2000 Elsevier Science B.V. All rights reserved.