Electron Scattering within SEM Specimen
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Multiple scattering normally does not occur within a thin TEM specimen but is significant within a thick SEM specimen where the primary electrons lose most or all of their energy. Table 4102 lists the thickness dependence of electron scattering from a specimen in EM (electron microscope) measurements.

Table 4102. Thickness dependence of electron scattering from a specimen in EM (electron microscope) measurements.
Scattering direction
EM method
Scattering event/angle
Scattering direction
Electrons
Wave (phase) property
Electron property
Contrast interpretation
Thin specimen TEM Less scattering events and then smaller scattering angle
Forward scattering More electrons Strong coherent signal Strong wave property Easy

Back scattering Fewer electrons Weak incoherent signal Weak particle property  
Thick specimen TEM/SEM   Forward scattering Fewer electrons Weak coherent signal Weak wave property Middle
Electron is scattered more than once (plural scattering), and then scattering angle is greater Back scattering More electrons Strong incoherent signal Strong particle property  
Very thick or bulk specimen SEM More scattering events and then greater scattering angle Forward scattering Fewest electrons Weakest coherent signal Weakest wave property Difficult
Electron is scattered >20 times (multiple scattering), and then scattering angle is greatest Back scattering Most electrons Strongest incoherent signal Strongest particle property  

 

Figure 4102 shows the coherence of various scattered electron rays from TEM and SEM specimens.

Coherence of various scattered electron rays Coherence of various scattered electron rays
Figure 4102. Coherence of various scattered electron rays: (a) Thin film specimen in TEM and/or STEM modes, and (b) Bulk specimen in SEM mode. The electron rays in red are incoherent, while the rays in green are coherent.

 

 

 

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