Electron energy loss spectroscopy in the electron microscope

Abstract

Abstract In a transmission electron microscope, the incident electrons travelling through the specimen thin foil can lose energy in inelastic interaction processes with the target electrons. The analysis of these energy loss transfers, designed as Electron Energy Loss Spectroscopy, is thoroughly described in this review, written in 1984. Relying on the basics of inelastic scattering theory, two major families of excitations are accounted for: (i) the low energy loss region (in the few eV range) where collective excitations (plasmons) and interband transitions of the electrons gas in the valence and conduction bands are generated; (ii) the high energy loss region (from typically 50 to a few thousand eV) where inner shell excitations detected above a continuously decreasing background, correspond to the ionization of electrons initially on atomic core levels. The intensity of these characteristic signals gives access to quantitative measurements of the number of excited atoms while their fine structures can be related to local electronic states (valence, bonding, structural environment). After a rapid survey of the latest instrumental developments at the time of writing, the review is focused onto the impact of EELS as an analytical tool for elemental analysis with high spatial resolution, addressing major issues in detection limits, minimum detectable mass and mass fraction.