Study of metals by transmission electron microscopy (TEM)

This dossier takes a practical look at the formation of the overall image in transmission electron microscopy (TEM), which is obtained in a number of different ways. The key point is the position of the contrast diaphragm, which lies in the focal plane of the objective lens. The various types of contrast, including diffraction, interference (phase contrast) and Z-contrast (used in STEM, transmission scanning electron microscopy) are listed in this text.

Electron energy and source quality (field emission, LaB ₆ emissive cathode, etc.) are also of prime importance. Correcting lens aberrations, particularly spherical aberration, greatly improves resolution, since it can now be better than a tenth of a nanometer (it can reach 0.05 nm).

It has been shown that the contrast of an image is profoundly linked to the various reflections that make up the diffraction pattern (for example, in the study of precipitates).

The high-resolution mode (interference contrast) allows us to observe the so-called structural image which, depending on the microscope's resolution, reveals columns or small groups of atomic columns. In this approach, crystalline defects can be observed and their characteristics determined, but a number of precautions must be taken, depending on the level of information required. The use of image simulation codes has become indispensable.

The dossier briefly touches on holography, which can be used, for example, to study electrical potential distributions in thin sections of transistors.