The diffraction pattern

In electron backscatter diffraction (EBSD) a beam of electrons is directed onto a tilted crystalline sample in a scanning electron microscope (SEM).  The electrons undergo various interactions with the atoms in the crystal lattice and some of the electrons emerge from the sample.  If a fluorescent phosphor screen is placed close to the sample a pattern is formed on the screen  because the intensity of the emerging  electrons varies slightly with direction.   This pattern is called a diffraction pattern and its appearance is very striking.

Unfortunately, there is no simple analogy in the everyday world for the physical phenomena of diffraction that causes the patterns .  The symmetry and appearance of the pattern is related intimately to the crystal structure at the point where the beam meets the sample.    If  the crystal rotates (in other words its orientation changes) the diffraction pattern will be seen to move .  If a different type of material is placed under the beam, the diffraction pattern will change completely.  So the diffraction pattern can be used to measure crystal orientations and to identify materials.