The Forbidden 222 Electron Reflection from Germanium

The strength of the forbidden 222 reflection in reflection electron diffraction patterns from a slightly etched (111) face of a germanium single crystal is shown to be independent of crystal orientation. It is thus due to `systematic interaction' rather than `accidental interaction'. The strength of the 222 ring from evaporated, polycrystalline germanium films has been studied as a function of particle size in the range 70 to 300 A and with accelerating voltage in the range 20 to 200 kV, and has been compared with values calculated from Hoerni's theory, and from Fujimoto's theory with Fujiwara's relativistic correction. At the larger values of λ D , at which Fujimoto's expansion cannot be used, agreement between Hoerni's theory and experiment is satisfactory. At lower values of λ D the calculated 222 intensity with relativistic correction is 50% higher than the experimental value.