12.3 Electron Microscopy 293
• Deceleration of the electrons in the electric field of the atomic nucleus, leading
to the emission of “bremsstrahlung” (radiation of deceleration). Bremsstrahlung is characteristic of the deceleration process; however, it is not characteristic
of the specimen. Bremsstahlung has a continuous spectrum with a maximum
energy equal to the energy of the incoming electrons.
• Ionization of inner shells of the atoms. This process leads to the emission
of characteristic X-rays. This emission is characteristic of the elements in
the specimen and is used for qualitative and quantitative analysis of the
specimen.
Ionization of an inner shell leads an electron vacancy in an inner shell; which
is filled by transfer of an electron from a more outer-lying shell. This process is
connected to an emission of the excess energy as an X-ray photon, which is characteristic of the emitting atom. Depending on the shell from where the electron was
expelled, and the one delivering the electron to fill this vacancy, characteristic X-rays
are grouped into different series. Figure 12.12 displays the system graphically.
Complementing Figure 12.12, Table 12.1 gives a compilation of some of the
X-ray emission series for elements, where the largest principal quantum number
n = 4. In the periodic system of the elements, this system of emission series is
continued up to a maximum principal quantum number n = 7.
The emitted characteristic X-rays allows unequivocal identification of the atoms
in the specimen. The wavelength of the emitted X-rays follows Moseley’s law:
ν α
β
=
−
(
)
Z
2
.
(12.17)
In Eq. (12.17) ν is the frequency of the emitted X-ray line, Z the atomic number
of the emitting element and the quantities α and β are constants depending on
Figure 12.11 Electrons and photons leaving the specimen after passage of energy-rich
electrons for image formation. Each one of these signals carries specific information about the
specimen and its composition.
Primary
electrons
Auger
electrons
InelasƟcally
scaƩered electrons
Specimen
ElasƟcally
scaƩered electrons
X-rays
Secondary
electrons
• Deceleration of the electrons in the electric field of the atomic nucleus, leading
to the emission of “bremsstrahlung” (radiation of deceleration). Bremsstrahlung is characteristic of the deceleration process; however, it is not characteristic
of the specimen. Bremsstahlung has a continuous spectrum with a maximum
energy equal to the energy of the incoming electrons.
• Ionization of inner shells of the atoms. This process leads to the emission
of characteristic X-rays. This emission is characteristic of the elements in
the specimen and is used for qualitative and quantitative analysis of the
specimen.
Ionization of an inner shell leads an electron vacancy in an inner shell; which
is filled by transfer of an electron from a more outer-lying shell. This process is
connected to an emission of the excess energy as an X-ray photon, which is characteristic of the emitting atom. Depending on the shell from where the electron was
expelled, and the one delivering the electron to fill this vacancy, characteristic X-rays
are grouped into different series. Figure 12.12 displays the system graphically.
Complementing Figure 12.12, Table 12.1 gives a compilation of some of the
X-ray emission series for elements, where the largest principal quantum number
n = 4. In the periodic system of the elements, this system of emission series is
continued up to a maximum principal quantum number n = 7.
The emitted characteristic X-rays allows unequivocal identification of the atoms
in the specimen. The wavelength of the emitted X-rays follows Moseley’s law:
ν α
β
=
−
(
)
Z
2
.
(12.17)
In Eq. (12.17) ν is the frequency of the emitted X-ray line, Z the atomic number
of the emitting element and the quantities α and β are constants depending on
Figure 12.11 Electrons and photons leaving the specimen after passage of energy-rich
electrons for image formation. Each one of these signals carries specific information about the
specimen and its composition.
Primary
electrons
Auger
electrons
InelasƟcally
scaƩered electrons
Specimen
ElasƟcally
scaƩered electrons
X-rays
Secondary
electrons