Electron microscopy
 
Thickness of EM Samples
- Practical Electron Microscopy and Database -
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Microanalysis | EM Book                                                                                   https://www.globalsino.com/EM/        


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Table 1217a. 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  

 

Table 1217b. Optimized sample thickness for various TEM measurements.
Technique
Quality
Thickness range
Resolution
TEM
Good ≤50 nm Tool resolution
Applicable 50 ~ 70 nm  
HRTEM
Best 10 ~ 25 nm Tool resolution
Applicable 25 ~ 100 nm  
(ADF-)STEM
Best 25 ~ 50 nm ≤ 0.3 nm
Applicable 50 ~ 90 nm ≤ 1.2 nm
TEM + DSE*
Applicable 200 ~ 600 nm  
CBED for strain analysis
Applicable 200 ~ 500 nm  
Holography
Applicable 150 ~ 300 nm  
EFTEM/EELS
Best 25 ~ 50 nm (depending on V and Z)** 0.3 ~ 0.5 nm
Ok 50-100 nm  
EDS
Applicable 50~100 nm 1 ~ 2 nm
* Dopant selective etching.
** V: Beam energy, Z: atomic number.

 

 

 

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