Kikuchi Patterns in a High Voltage Electron Microscope

In a high voltage electron microscope, the Kikuchi patterns from low index planes change considerably as the accelerating voltage is raised above 100 kV. These changes, which result from many-beam interactions among the systematic reflections, are studied in detailat' 100 to 1000 kV in f.c.c, b.c.c., and h.c.p, metals having a wide range of atomic numbers. In addition, a new method for calculating both conventional and high voltage Kikuchi patterns is given. The method is based on a simple theoretical relationship between Kikuchi patterns and many-beam rocking curves, and thus avoids the mathematical complications of previous theories of Kikuchi patterns. This method also leads to considerable physical insight into Kikuchi patterns and into their relation to the diffraction channelling behavior of electrons in crystals, and explains, for the first time, the anomalous 100 kV Kikuchi patterns from the (111) planes of diamond cubic materials.