Links in this section:

Introduction
Fundamentals of the TEM technique
Beam-sample interaction
The Analytical TEM
Detector Protection
Qualitative Analysis
Quantitative Analysis
Microanalysis Examples (1)
Microanalysis Examples (2)
Microanalysis Examples (3)
Summary

Basics of electron beam-sample interaction in the TEM

While the overall concept remains the same, Energy Dispersive X-ray Analysis in Transmission Electron Microscopy reveals some marked differences from EDS analysis in the Scanning Electron Microscope (SEM). Normally, SEM samples are thick enough for the focussed probe to be contained within the sample, i.e. complete absorption of the primary beam. This causes the beam to spread within the material and leads to a number of different phenomena that affect the analytical treatment of raw X-ray counts obtained from the material. These include atomic number (Z), absorption (A) and fluorescence (F) effects, which are dealt with by applying matrix corrections. The incident beam energy, material density and take off angle therefore have a profound affect on X-ray intensity and quantitative results in the SEM.

In contrast, TEM samples should be thin enough to be beam transparent, so the ionization volume formed by a focussed probe is much smaller and, therefore, there is much less electron scattering (Figure 2). High beam energies (commonly between 100kV - 400kV) utilized in the analytical TEM also reduce beam scattering. However, due to the relatively small ionization volume, X-ray generation is much lower than for thick samples. When analyzing thicker samples in TEM, absorption corrections may be made if the material density and thickness at the point of analysis are known, whereas these corrections are not always necessary in thin samples.

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