Beam Spreading in STEM Caused by Chromatic Aberration
- Practical Electron Microscopy and Database -
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In STEM mode, beam spreading caused by chromatic aberration dc can be given by,

          Beam Spreading in STEM Caused by Chromatic Aberration ---------------------------------- [2237]

where,
         ΔE -- The energy spread of the electron beam;
         E0 -- Eenergy of incident electron beam;
         α -- The convergence semi-angle;
         Cc -- The non-relativistic chromatic aberration and its coefficient.

From Equation 2237 we know that both Cc and ΔE should be low enough in order to suppress beam spreading at low acceleration voltages, especially Cc depends strongly on the accelerating voltage.

 

 

 

 

 

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