Secondary Electron Emission Spectroscopy

Abstract

When an electron with energy E _p (in practice 10 < E _p < 500 eV) is incident on a solid surface it may be scattered back into the vacuum either elastically or inelastically. Part of its energy, however, passes through a series of collisions (cascade) to other (secondary) electrons, and some of these secondary electrons are emitted from the solid. Obviously, in practice one cannot distinguish between a primary backscattered electron and an emitted secondary electron, and, therefore, the distinction between the two is made for convenience, on a rather artificial basis. This is better explained by reference to Fig. 10.1, which shows a typical energy distribution of the electrons emitted from a metal surface. The electrons in region III correspond to elastically scattered electrons and electrons which have collided with phonons losing energy of the order of a few hundredths of an eV. Electrons which lost more energy appear in region II. This region is characterized by certain peaks corresponding to inelastic collisions of the incident (primary) electron with plasmons (collective oscillations of the electrons) and with other electrons. The energy of these peaks is fixed relative to the primary energy (they lie between 2 and 50 eV below it) and is determined by the excitation energy of plasmons and of interband electronic transitions. Region I consists of the true secondary electrons which are generated by the cascade process. In this chapter we are exclusively concerned with the electrons in this region, referring to them, simply, as secondary electrons. Because of the series of (random) collisions that (presumably) occur between the initial one (involving the incident electron) and the final event, i.e., the escape of the secondary electron from the metal, the latter should retain very little information about the incident electron.