LabAdviser/314/Microscopy 314-307/SEM/Nova/Transmission Kikuchi diffraction: Difference between revisions

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 = Kikuchi lines =
-The formation of Kikuchi patterns can be described as a two-step process, as shown schematically in Fig. 1.
+The formation of Kikuchi patterns can be described as a two-step process, as shown schematically in Fig. 1. The first step consists of an incoherent inelastic, large angle scattering process of the primary beam electrons, producing a point-like electron source inside of the crystal. The second step is the elastic and inelastic coherent
+scattering of these electrons by the crystal planes of the material: the electrons can be Bragg reflected at lattice planes with reciprocal lattice vector -g if the Bragg angle is ±0_B or if the direction of incidence k_0 lies on one of the Kossel cones, which have an aperture 90°- 0_B and the g direction (normal to the lattice planes) as axis. There is a pair of Kossel cones for g, another pair for 2g and so on. The intersection between the Kossel cones and the plane of observation results in the formation of Kikuchi lines. The intersection is an hyperbola, but the lines are approximately straight owing to the low value of 0_B. The formed Kikuchi lines do not have the same intensity: one line, called the excess line, is brighter than the other, called the defect line.
-[[File:Picture11.png|300px|center|thumb|Fig. 1: Schematic representation of Kikuchi lines formation.]]
-The first step consists of an incoherent inelastic, large angle scattering process of the primary beam electrons, producing a point-like electron source inside of the crystal. The second step is the elastic and inelastic coherent
+[[File:Picture11.png|400px|center|thumb|Fig. 1: Schematic representation of Kikuchi lines formation.]]
-scattering of these electrons by the crystal planes of the material: the electrons can be Bragg reflected at lattice planes with reciprocal lattice vector -g if the Bragg angle is ±0_B or if the direction of incidence k_0 lies on one of the Kossel cones, which have an aperture 90°- 0_B and the g direction (normal to the lattice planes) as axis. There is a pair of Kossel cones for g, another pair for 2g and so on. The intersection between the Kossel cones and the plane of observation results in the formation of Kikuchi lines. The intersection is an hyperbola, but the lines are approximately straight owing to the low value of 0_B. The formed Kikuchi lines do not have the same intensity: one line, called the excess line, is brighter than the other, called the defect line.