Electron diffraction: parallel illumination

After detailing the characteristics of radiation-matter interaction and highlighting the differences between electron radiation, X-rays and neutrons in the [M 4 125] and [M 4 126] files, we will now turn our attention to electron diffraction obtained in practice with an electron microscope. These are high-energy electrons that interact strongly with the crystalline potential of a thin specimen in different experimental situations, thanks to the great flexibility of illumination conditions obtainable with a modern microscope.

Starting with a brief description of the basic principle of an electron microscope, we'll see how the conditions for diffraction at infinity (Fraunhoffer diffraction [M 4 126] ) are achieved. It will therefore be highly instructive to examine the "geometric" correspondence between a known two-dimensional object and its diffraction pattern obtained by Fourier transformation. Next, we'll look at the different ways of acquiring information in reciprocal space [M 4 125] , after briefly pointing out the fundamental consequence of fast electron diffraction.