Aggregation effects in the energy loss of swift H and He ions in SiC and TiC

Abstract

We use the dielectric formalism to evaluate the electronic energy loss of swift H and He ions in SiC and TiC targets, as a function of the projectile energy. The electronic properties of these materials are described by the MELF-GOS model, where the excitation of outer electrons is characterized by a linear combination of Mermin-type energy-loss functions (ELF), whereas the contribution due to the target inner-shell ionizations is included through hydrogenic generalized oscillator strengths (GOS). In this scheme, the differences between the energy loss of the projectile in the compound clearly differ from that calculated from its elemental component when applying Bragg’s additivity rule, which assumes that the energy loss in each species is unaffected by the state of aggregation. Our calculations show that the results provided by Bragg’s additivity rule fails near and below the stopping power maximum due to aggregation effects, which affect mainly the outer electrons excitation spectrum. We obtain that aggregation effects in the energy loss are more important for H projectiles in TiC targets. A good agreement with available experimental data is obtained.