Electron microscopy
 
Twofold Axis in Crystals
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Figure 1619a shows examples of two-fold rotation axis in crystallography.

two-fold rotation axes

Figure 1619a. Examples of two-fold rotation axes (from x, y, z to -x, -y, z.).

Figure 1619b (a) shows a two-fold axis, and Figure 1619b (b) shows the two-fold, three-fold and four-fold axes in a cubic structure.

two-fold axis
two-fold, three-fold and four-fold axis
   

Figure 1619b. (a) A two-fold axis, and (b) The two-fold, three-fold and four-fold axes in a cubic structure.

A vertical glide plane results in a mirror line in the CBED pattern. At Bragg condition, a horizontal twofold axis or twofold screw axis in the ZOLZ along g presents a mirror line of symmetry onto disk g, and this line runs normal to g.

 

 

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