Introduction

In 1949, Castaing and Guinier combined for the first time the technique of electron optics and X-ray analysis for the production of the first electron probe analyser (Castaing & Guinier, 1949). Developments continued during the years from a static beam instrument into a scanning device. However, all the analysis was initially limited to thick specimens and it was only at a later date that the first prototype microanalyser was specifically developed for thin specimens (Duncumb, 1962). The detection and counting of X-rays was done by using conventional wavelength dispersive crystal spectrometers. A major breakthrough in X-ray analysis came in 1968 with the development of the solid state energy dispersive X-ray detector (Fitzgerald, Keil & Heinrich, 1968). This type of detector provided higher collection efficiency than the wavelength dispersive spectrometer as well as more reproducible results because mechanical movements were no longer necessary.

Nowadays X-ray microanalysis is a well used technique for analysis of biological material in combination with the transmission and scanning electron microscopes. In this chapter new developments on the energy dispersive detectors will be discussed. Special attention will be given to the advantage of using a high purity germanium crystal instead of Si(Li) crystal in the EDS detector.

X-ray generation

When a focused electron beam hits a specimen several processes occur at the surface and in the specimen. In Fig. 1.1 a schematic presentation of the different interactions is presented.