Eels Near Edge Structures

The beginning of EELS near edge structure work in a transmission electron microscope with particular aim at comparing results to electronic structure calculations can be traced to Egerton and Whelan [1]. Later, Grunes and Leapman [2] also applied the method to study transition metal oxides and attempted to compare the experimental results to band structure calculations. Then followed more systematic electronic structure work at much higher energy resolution (but on a dedicated spectrometer with no spatial resolution) by Fink [3]. Presently, with the development of commercially available efficient parallel spectrometers and energy filters which are attached to transmission electron microscopes the possibilities have increased as different scientist enter the field with different backgrounds to study new problems. The quality of the spectra has become comparable, in terms of energy resolution, to the current synchrotrons [4] but with the clear and incomparable advantage of very high spatial resolution which now reaches the sub-nanometer level in standard commercial instruments. The applications of EELS have thus impressively increased in the last 10 years and a significant portion of these are beyond the microanalysis applications and concentrate on the variations of fine structure to identify various compounds and to probe the local coordination. Reviews of this type of work including energy filtering for elemental mapping can be found in the references of reviews on the technique [5–9]. The second edition of the book by Egerton in 1996 [9] shows the dramatic increase in the number of application of the technique due to the availability of the instruments (parallel spectrometers and energy filters) integrated in analytical transmission electron microscopes and dedicated scanning transmission electron microscopes. In the chapters by L.M. Brown and J.M. Howe included in this book, many examples are described.