As illustrated in Part I, Bragg reflections are the only beams expected to be observed in electron diffraction patterns of crystals. In practice, diffuse scattering, distributed at non-Bragg reflection angles, is seen, and some dark and bright line pairs and bands, so-called Kikuchi lines and bands, also appear in the pattern. These features are observed experimentally, as shown by a diffraction pattern of \(\alpha -\text {Al}_{2} \text {O}_{3}\) [11 \(\overline{2} 0\) ] in Fig. 6.1. The formation of a Kikuchi pattern is attributed to the inelastic-scattering effect in electron diffraction. In high-energy electron scattering, various inelastic-scattering events, such as phonons, plasmons (or valence electrons), and atomic inner shell electrons, can be excited because of the interaction of the incident electron with electrons and nuclei in the crystal. The result of each inelastic-scattering process is a transition of the crystal state due to energy and momentum transfers from the incident electron. Figure 6.2 shows a series of energy-filtered electron diffraction patterns of Si [111] of about 50 nm thickness, which exhibit the angular distribution of electrons with different energy losses (Reimer et al. 1990). The zero-loss filtered diffraction pattern (Fig. 6.2b) is much sharper than the unfiltered diffraction pattern (Fig. 6.2a). Bragg beams are apparent, especially in the zero-loss and plasmon filtered diffraction patterns.