Electron energy-loss spectrometry (EELS) is the analysis of the energy distribution of electrons that have interacted inelastically with the specimen. These inelastic collisions tell us a tremendous amount about the electronic structure of the specimen atoms, which in turn reveals details of the nature of these atoms, their bonding and nearest-neighbor distributions, and their dielectric response. In order to examine the spectrum of electron energies we almost invariably use a magnetic prism spectrometer which, when interfaced to a TEM, creates another form of AEM. The magnetic prism is a simple, but highly sensitive, device with resolving power of approximately 1 eV even when the energy of the incident electron beam is up to 400 keV. Despite its simplicity the magnetic prism is operator-intensive and there is not yet the degree of software control to which we are accustomed with XEDS. In this chapter we’ll describe the operational principles, how to focus and calibrate the spectrometer, and how to determine the collection semiangle (β). This angle is a most important parameter for interpreting your experimental data. In subsequent chapters we’ll go on to look at the spectra, the information they contain, and how we extract quantitative data and images from them. As with XEDS there are standard tests to determine that the spectrometer is working correctly, and we’ll describe these also.
David B. Williams, C. Barry Carter
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