Role of plasmon decay in secondary electron emission in the nearly-free-electron metals. Application to aluminum

Abstract

In this paper, a theoretical analysis of secondary electron emission in the nearly-free-electron (NFE) metals is presented. Restricting ourselves to excitation of secondary electrons (SE's) from the valence (or conduction) band only, we investigate the roles played by screened electron-electron scattering and by volume- and surface-plasmon decay in the excitation of SE's. Using the complex dielectric constant in the random-phase approximation we demonstrate that an important source of low-energy SE's may arise from the decay of long-wavelength surface and volume plasmons via near vertical interband transitions. A simple transport theory based on the work of Berglund and Spicer is developed to treat the SE escape problem approximately assuming an idealized model of the solid-vacuum surface barrier. Model calculations of the external SE energy distribution curve (EDC) and its derivative are presented for aluminum. The results are in reasonable agreement with some recent experimental EDC's obtained by a number of authors on clean al samples. We tentatively conclude that an appreciable contribution to the total number of low-energy SE's emitted from NFE metals under kilovolt electron bombardment may come from the decay of surface and volume plasmons into single-electron excitations.