An Introduction to Electron Energy-Loss Spectroscopy

Abstract

Electron energy-loss spectroscopy (EELS) involves analyzing the energy distribution of initially monoenergetic electrons, after they have interacted with a specimen. This interaction may take place within a few atomic layers, as when a beam of low-energy (100–1000 eV) electrons is “reflected” from a solid surface. Because high voltages are not involved, the apparatus is relatively compact, but the low penetration depth implies the use of ultrahigh vacuum; otherwise information is obtained mainly from the carbonaceous or oxide layers on the specimen’s surface. At these low primary energies, a monochromator can be used to reduce the energy spread of the primary beam to a few millielectron volts (Ibach, 1991), and provided the spectrometer has a comparable resolution, the spectrum contains features characteristic of energy exchange with vibrational modes of surface atoms, as well as valence-electron excitation in these atoms. The technique is therefore referred to as high-resolution electron energy-loss spectroscopy (HREELS) and is used for studying the physics and chemistry of surfaces and of adsorbed atoms or molecules. Although it is an important tool of surface science, HREELS uses concepts which are substantially different to those involved in electron-microscope studies, so it will not be discussed further in the present volume. The physics and instrumentation involved are dealt with by Ibach and Mills (1992).