The Basic Principles of Eels

Abstract

Electron energy-loss spectroscopy (EELS) studies the energy distribution of electrons that have been transmitted through a thin sample. By combining electron spectroscopy and transmission electron microscopy, the analytical power of EELS is coupled with the ability to select, image, and obtain diffraction patterns from small areas. Although the use of EELS as a microanalytical technique was first discussed and demonstrated forty years ago by Hillier and Baker (1944), it is only recently that advances in microscope instrumentation and vacuum technology have made it a practical proposition for routine laboratory use. Like the technique of energy-dispersive x-ray spectroscopy (EDXS) discussed in the previous chapters, electron energy-loss spectroscopy provides a way to identify the elements in the sample and to quantify the amount of each. Since EELS can also detect low-atomic-number elements with high sensitivity, it can offer important advantages over EDS in some applications. In addition, EELS can provide detailed information about the electronic state and chemical bonding of the sample. This chapter describes the principles and practice of obtaining and interpreting EEL spectra, and the following chapters discuss the application of these ideas to problems in materials science and biology.