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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:
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Beam-sample interaction at at a proper overvoltage |
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Electron of inner-shell is removed by an electron of the incident beam |
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A vacancy in the shell is generated (the atom remain ionized for 10-14 second) |
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An electron of outer-shell fills the vacancy of the inner-shell |
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During this filling transition, a X-ray photon is emitted with a characteristic energy of the chemical element and its shell ionized |
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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:
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Beam-sample interaction at at high overvoltages |
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More than one electrons of inner-shell are simultaneously removed by an electron of the incident beam |
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More than one vacancies in the shell are generated (the atom remain ionized for 10-14 second) |
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More than one electrons of outer-shell fill the vacancies of the inner-shell |
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This simultaneous filling transition causes a change in the overall structure of the energy levels |
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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:
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Beam-sample interaction |
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Auger process |
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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:
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Beam-sample interaction |
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Deceleration of the electron beam in the Coulombic field of
the specimen atoms |
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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.
Figure 4690. Various wavelengths of lights, microwave, radio, and incident electrons in EMs.
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