General considerations

Introduction

A large number of surface techniques involve the detection of electrons in the energy range 5–2000 eV which are emitted or scattered from the surface. A number of features are common to most of these techniques. In particular, all derive their surface sensitivity from the fact that electrons in this energy range have a high probability of inelastic scattering, so that if electrons are detected at an energy which is known to be unchanged by passage through the surface region of the solid, we know that they have passed only through a very thin surface layer; i.e. the techniques are surface specific. Secondly, because this surface specificity derives from a knowledge of the energy of the electrons, some form of electron energy analyser is required by most of these techniques. This piece of instrumentation is therefore common to many techniques.

Of course, no classification scheme is perfect. Electron energy analysers can also be used to determine the energy spectrum of other charged particles, notably ions as in ion scattering spectroscopy. Inverse Photoemission Spectroscopy (IPES) and Appearance Potential Spectroscopy (APS) are not strictly electron spectroscopies as ultraviolet and X-ray photons are detected, but IPES is very closely related to photoemission in the basic physics, and both share with electron spectroscopies a surface specificity which is governed by electron inelastic scattering.