Electron microscopy
  
Beam Intensities at Two-Beam Diffraction Condition
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Table 1235. Beam intensities at ideal two-beam conditions when inelastic scattering is negligible.

Sample thickness (t) Intensity of direct beam (%) Intensity of diffracted beam (%)
ξg/4 50 % 50 %
ξg/2 0 % 100 %
> ξg/2 Increases with increasing thickness Decreases with increasing thickness
ξg 100 % 0 %
*ξg: Extinction distance (see table).

Note the oscillation of direct and beam intensities give rise to the thickness or Pendellösung fringes that can be seen in TEM images if a relatively small objective aperture is used.

 

 

 

 

 

 
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