Introduction

Abstract

Studies of low-energy backscattered electrons, secondary electrons and absorbed electron depth distribution, have all been of great interest for many analytical techniques. Indeed, a better understanding of the collision events occurring in the surface layers before the emission of backscattered and secondary electrons, should allow a more general comprehension of surface physics. The problem of backscattered and secondary electron emission from solids irradiated by a particle beam is of crucial importance, especially in connection with the analytical techniques that utilise secondary electrons to investigate chemical and compositional properties of solids in the near surface layers, i.e. Auger electron spectroscopy and X-photoelectron spectroscopy. The electron backscattering coefficient is a quantity which, for slow primary electrons and for supported and unsupported thin films, requires theoretical, numerical and experimental investigation. The energy spectra of secondary electrons emitted by solid targets and stimulated by particle beams are very complicated because many features appear in the spectra due to the different collision processes involved prior to low-energy secondary electron emission. Accurate knowledge of the depth distribution of trapped electrons in dielectric materials (biological materials, ceramics, glass) is necessary to solve the diffusion equation in order to investigate the charging phenomena, while the study of positron depth distribution in solids is required for positron annihilation spectroscopy, a technique that allows non-destructive investigations of structural defects at surfaces and interfaces.