Electron diffraction in metals and alloys: convergent illumination

In the three previous dossiers, we described the conditions for electron-matter interaction [M 4 125] , the essential basics of crystallography [M 4 125] and diffraction conditions in parallel illumination situations [M 4 126] for which the incident beam is characterized by the wave vector, noted k, of a plane wave [M 4 125] . Two cases have been commented on [M 4 127] : one where the incident parallel beam is spatially extended and therefore illuminates a large area of the sample, for which the region from which we recruit diffraction information is limited by a diaphragm (this is the area selection diffraction technique), and one where the incident parallel beam is not spatially extended and illuminates a small area of the sample (the conditions are those of microdiffraction and no selection diaphragm is used).

These two conditions provide a wealth of information, and, especially in the area-selective mode, they always constitute the initial stage of observation. If the crystal is known or predictable, the examination of several orientations enables us to check that the reciprocal lattice observed corresponds to that predicted for the crystal whose elementary mesh is known or assumed. Each of the crystal orientations, accessible using the goniometric stage, corresponds to a planar...