Kikuchi patterns in high voltage electron microscopy

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Abstract
Kikuchi diffraction patterns (K-patterns) from low index planes of various crystals were studied as a function of electron accelerating voltage and planar inclination to the beam of a 100 to 1100 kv electron microscope. These patterns, many of which are shown for the first time, are predicted semi-quantitatively by a simple theory that relates K-patterns to electron transmission rocking curves. Although intended mainly to account for the effects of many-beam systematic interactions at high voltages and multiple inelastic scattering important in relatively thick crystals, the theory also gives new insight into such features of conventional 100 kv K-patterns as excess-deficit K-line pairs, thickness oscillations of K-line contrast, and fine structure. It also predicts and explains in terms of electron transmission behaviour, the vanishing of K-lines at ‘critical’ voltages, a new critical voltage effect from (111) planes of diamond cubic crystals, and the characteristic behaviour of K-patterns accompanying important changes in the transmission and defect image contrast at high voltage. Computer-generated K-pattern facsimiles have been used extensively to facilitate comparison of predicted and experimental patterns.