High-angle Kikuchi patterns

Abstract

A cylindrical specimen chamber and camera have been used to study the high-angle Kikuchi patterns obtained by reflexion of electrons, of energy 6 to 50 keV, from the cleavage surfaces of crystals with the sodium chloride structure. Angles of scattering ranging from 0 to 164° were covered. The relative intensity of the pattern at different scattering angles was measured using a photographic technique. The intensity distribution was found to become less steep as the energy of the incident electrons decreased. In photographs taken with a large value of the glancing angle of incidence, defect bands were found, starting near the shadow edge of the pattern; these changed to excess bands at higher angles of scattering. The most striking feature of the results is the remarkable intensity and clarity at the highest scattering angles of the pattern produced by crystals such as lead sulphide and potassium iodide, the constituents of which have a relatively high elastic scattering cross-section. In marked contrast, a relatively low intensity and low clarity was found at these angles for lithium fluoride under the same experimental conditions. An investigation of the width of Kikuchi bands, visible over the whole available angular range, showed that the electrons forming these bands had the same energy as that of the incident electrons within the experimental error of 10%. A possible mechanism is discussed by means of which electrons can be diffused through large angles with high efficiency, relative to small angles, and with relatively little loss of energy.

The Theory of Kikuchi patterns

“…Among them are those of Shinohara & Matsukawa (1933), Boersch (1937 and Pfister (1953), who observed that Kikuchi bands in transmission patterns change from defect to excess, or vice versa, with the change of the energy of the incident electrons and with the change of the thickness of the crystal. Alam, Blackman & Pashley (1954) observed a similar effect for the intensities of Kikuchi bands in reflexion patterns when the angle of incidence is changed. The failure of the present theory to cover these observations is due to our assumption that ~i(r) is very small compared with q%(r).…”

Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope

“…patterns (Alam et al, 1954;Venables and Harland, 1972;Dingley, 1981;; Dingley and Baba-Kishi, SELECTED area electron channelling patterns (Coates, 1990;Dingley and Randle, 1992;Randle, 1992;Day, 1967;Joy, 1974;Joy et al, 1982;Davidson, 1984; both provide quantitative data concerning Lloyd, 1985;1987;Schmidt and Olesen, 1989; Lloyd spatial variation of crystallographic orientations Lloyd, 1995) and electron backscatter minerals. In many problems relevant to geologists, Mineralogical Magazine, December 1996, Vol.…”

Back-scattered electron visualization of ferroelectric domains in a BiFeO3 epitaxial film

“…Scanning across ferroelectric domains will result pattern geometry and intensity variations which may be detected by our TLD detector sampling a small area of the pattern. Support for this idea comes from the early EB diffraction work of Alam et al, 27 which demonstrates that the commonly used electron backscatter diffraction orientation (EB ~70° incidence to surface normal) produces strong scattering but those patterns also exist at high angles back along the incident beam direction. For all EB diffraction from bulk samples there is combined diffuse and elastic scattering, which gives rise to the Kikuchi bands in diffraction patterns.…”