Introduction of X-Ray and X-Ray Generation
- Practical Electron Microscopy and Database -
- An Online Book -

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The "perfect" characteristic X-rays are generated by the atoms of the sample in a process called inner-shell ionization at a proper overvoltage. Such generation process is:

  Beam-sample interaction at at a proper overvoltage
 
Electron of inner-shell is removed by an electron of the incident beam
   
A vacancy in the shell is generated (the atom remain ionized for 10-14 second)
     
An electron of outer-shell fills the vacancy of the inner-shell
       
During this filling transition, a X-ray photon is emitted with a characteristic energy of the chemical element and its shell ionized
         
The emitted X-ray photons are named by the shell-ionized type as K, L, M lines.... and α, β, γ... by the outer-shell corresponding to the electron that filled the inner-shell-ionized

The satellite X-ray peaks can be generated at high overvoltages. Such generation process is:

  Beam-sample interaction at at high overvoltages
 
More than one electrons of inner-shell are simultaneously removed by an electron of the incident beam
   
More than one vacancies in the shell are generated (the atom remain ionized for 10-14 second)
     
More than one electrons of outer-shell fill the vacancies of the inner-shell
       
This simultaneous filling transition causes a change in the overall structure of the energy levels
         
Produce X-rays with slightly lower energies than the normal characteristic X-rays, which are called satellite peaks

The satellite X-ray peaks can also be generated by Auger process. Such generation process is:

  Beam-sample interaction
 
Auger process
   
Produce X-rays with slightly lower energies than the normal characteristic X-rays, which are called satellite peaks

Bremsstrahlung radiation or continuum X-rays are generated by deceleration of the electron beam in the Coulombic field. Such generation process is:

  Beam-sample interaction
 
Deceleration of the electron beam in the Coulombic field of the specimen atoms
   
Bremsstrahlung radiation or continuum X-rays are produced (photons emitted with any energy value)

Two types of X-rays are induced by the incident electron beam: characteristic X-rays and Bremsstrahlung X-rays.

Table 4690. X-rays detected by EDS detectors in EMs.

X-rays Origin Intensity level Remark
Characteristic X-rays Electron beam hits at probing spot on specimen Highest Signal
Scattered electrons hit everywhere on specimen Second highest Artifact
Scattered electrons hit on EM holder, chamber, and apertures Lower Artifact
Higher-energy X-rays hit everywhere on specimen Lower Artifact
Higher-energy X-rays hit on EM holder, chamber, and apertures Lower Artifact
Sum peak Two x-rays arrive at the detector at the same time Lower Artifact
Escape peaks (Some small fraction of the counts of the main peak)

Incoming x-ray may fluoresce silicon atoms in the detector

Lower Artifact
Silicon internal fluorescent peak Incoming x-ray may fluoresce silicon atoms in the detector Very low Artifact
Bremsstrahlung X-rays (increase as X-ray energy decreases) Electron beam hits at probing spot on specimen Low Artifact
Scattered electrons hit everywhere on specimen Low Artifact
Scattered electrons hit on EM holder, chamber, and apertures Low Artifact
Higher-energy X-rays hit everywhere on specimen Low Artifact
Higher-energy X-rays hit on EM holder, chamber, and apertures Low Artifact

Figure 4690 shows the wavelengths of gamma ray, x-ray, ultraviolet, visible light, near infrared, far infrared, microwave, radio, and incident electrons in electron microscopes.

wavelengths of gamma ray, x-ray, ultraviolet, visible light, near infrared, far infrared, microwave, radio, and incident electrons in electron microscopes

Figure 4690. Various wavelengths of lights, microwave, radio, and incident electrons in EMs.

 

 

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