Kikuchi lines and bands

Now the inelastically scattered beams from P fan out in three dimensions. All the beams, such as a, and the corresponding Bragg diffracted 

In practical electron microscopy, it is often important to be able to determine accurately the deviation A0 from the exact Bragg angle 0. We now consider in some detail how we can use Kikuchi lines for doing this. 

A rotation of 20 would cause the Kikuchi lines to move through a distance X. Thus, AX] and A0j are related by the equation 

By drawing similar diagrams for higher-order reflections (3g, 4g, etc.) satisfying the Bragg condition, we can easily see that if a reciprocal lattice point G of the systematic row lies on the Ewald sphere (i.e., s g = 0), then the magnitude of the diffraction error Sg of the first-order reflection will be given by 

This equation is particularly useful when setting up for weak-beam dark field imaging, to be discussed in Chapter S. 

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