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  Kikuchi Lines - 2     6 of 8

Kikuchi Line Construction 1(1) Electrons which have been inelastically scattered can subsequently be diffracted, but only if they are now travelling at the Bragg angle, qB to a set of planes.

(2) Two sets of electrons will be able to do this - those at +qB and those at -qB.

(3) This diffraction results in intensity changes in the background.  Because there are more electrons at A than B  (since electrons passing through A are closer to the incident direction than those through B) one bright line is developed (the excess line) together with one dark line (the deficit line).

Kikuchi "Cones"(4) Because the electrons are inelastically scattered in all directions, the diffracted electrons will form a cone, not a beam.  Hence we observe Kikuchi lines - not Kikuchi spots!

(5) The spacing of the pair of Kikuchi lines is the same as the spacing of the diffracted spots from the same plane.  However, the position of the lines is very sensitively controlled by the orientation of the specimen and Kikuchi lines are often used to set the orientation of a crystal in the TEM to an accuracy of 0.01 degrees.



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