6 - Analysis in the electron microscope

Summary

Although the moving force behind the development of electron microscopes was the potential of shorter wavelength illumination to reveal finer detail than the light microscope, the richness of interactions between specimen and the illumination makes the electron microscope capable of determining much more than morphological structure. In addition to the analysis of sizes and shapes already mentioned (Image Analysis, Chapter 5) it is possible to obtain information on the elemental composition of specimens, and in the TEM about any crystalline compounds which are present. All this on a micrometre scale at worst, and at best down to sub-nanometre dimensions. On some specimens surface and bulk compositions can be distinguished and the presence and distribution of impurities can be shown.

This chapter will describe the types of analysis possible in electron microscopes, using the techniques:

Electron diffraction

X-ray microanalysis

Electron energy loss spectroscopy

Auger electron spectroscopy

Cathodoluminescence

Electron diffraction

Electron diffraction in the TEM

In the TEM the strong interaction between crystalline specimens and the electron beam can be used to derive crystallographic information in a number of different ways. Not all are possible on all microscopes.

High-resolution diffraction

It is possible to use many commercial TEM columns as conventional diffraction cameras (Chapter 2, page 52–3), with camera length typically about 300–400 mm and very well-resolved patterns because the illuminating spot can be made very small.