Electron probe X-ray microanalysis - Principle and instrumentation

Electron probe X-ray microanalysis can best be described as a "chemical analysis method on the scale of $\mu m^3$ ". It involves analyzing the characteristic X-ray spectrum generated in a target by a finely focused electron beam.

The idea of using an electron beam to analyze the chemical composition of a sample was born in the 1940s and has been the subject of numerous studies in various countries (V.E. Cosslett in Great Britain, I.B. Borovski in the USSR, J. Hillier in the USA...). At the Delft Congress in 1949, Raimond Castaing (1921-1998) presented the first microprobe, which he built at ONERA under the direction of André Guinier [13][14] . This was followed in 1955 by two prototypes (one of which was installed at IRSID), and in 1958 by the first commercial instrument, designed by CAMECA under the name "MS85".

At present, a distinction can be made between :

• on the one hand, the electron probe X-ray microanalyzer, known in France as the "microsonde de Castaing", which uses X-ray spectrometers with monochromator crystals (WDS wavelength-dispersive spectrometers), but also scanning electron imaging;

• and, secondly, X-ray microanalysis as an analytical complement to scanning and transmission electron microscopy, using mainly solid-detector X-ray spectrometers (EDS energy-selective spectrometers).

In principle, there is little to distinguish a Castaing electron microprobe from a scanning electron microscope [2][15] . The electron column consists of an electron source and several electromagnetic lenses designed to focus the beam on a target (the sample to be analyzed). The X-rays generated are then analyzed by one or more X-ray spectrometers. The volume of the emission zone is typically of the order of m ³ . In addition to the small volume analyzed, the main advantage of this technique lies in the various possibilities for quantification, and in particular in the high level of precision achieved.

The present article is devoted to theoretical and instrumental aspects; applications are studied in the