allows obtaining detailed knowledge about energy levels and possible transitions—
a key information from the point of view of effective laser working. UV-Vis
spectroscopy is also widely used in analytical chemistry, e.g., to determine the
concentration of ions, molecules, or functional groups responsible for individual
absorption peaks.
Electron spectroscopy methods [9–12] (XPS—X-ray photoelectron spectroscopy, UPS—ultraviolet photoelectron spectroscopy, or AES—Auger electron
spectroscopy) measure the kinetic energy of electrons emitted from the material as a
result of exposure to high energy ionizing radiation or high energy particles
bombardment. The main difference between XPS and UPS methods is in the atomic
shells which can be studied: The inner shells electrons can be ejected using higher
energy X-rays (frequencies around 10
18 Hz), while valence shells electrons can be
ionized using lower energy ultraviolet light with the frequencies about 10
16 Hz. The
kinetic energy of electrons measured by these methods is equal to the difference
between the energy ht of the used incident radiation and the binding energy
(ionization potential) of the emitted electron and depends strongly on the type of
atom from which the electron was emitted, its oxidation state, and its immediate
environment; whereby it is possible to use these techniques to identify the atoms of
a given element in the material, providing the basis for electron spectroscopy for
chemical analysis (ESCA) developed by Siegbahn et al. [13].
The method directly related to the XPS and UPS spectroscopy is the Auger
electron spectroscopy [11, 14], in which emitted electrons are not the electrons
primary ionized by X-ray or ultraviolet radiation, but the product of secondary
processes, i.e., decay of ionized atoms from excited states to lower energy states
associated with emission of a photon, which can be emitted (and measured by XPS
or UPS) or absorbed by the electron from outer shells, resulting in the emission of
such secondary ionized electron (called the Auger electron). Electron spectroscopy
methods are very important and useful methods to determine energy levels in atoms
and molecules. In the case of solids, they are particularly useful for studying the
local structure of the surface of materials, since due to the relatively low energy of
emitted electrons and their strong dissipation in the material, in practice it is possible to observe only electrons ejected from the surface layer with a thickness of up
to 5 nm.
Even higher energies than those used in electron spectroscopy require processes
of transitions between energy levels of atomic nuclei (around 10
19 Hz). The method
that examines such processes is the Mössbauer spectroscopy [15, 16], based on the
Mössbauer effect (i.e., resonant and recoil-free emission and absorption of c-rays by
atomic nuclei in a solid). In Mössbauer spectroscopy, three types of nuclear
interactions are observed:
• Isomer shift (energy shift of the absorption peak resulting from the modification
of the energy levels of the nucleus by changes in the distribution of electron
density in the atom, due to the changes in the local environment of the atom; this
shift may, e.g., correlate with the electron density at atomic nucleus of the outer
s shells electrons);
4
A. Koleżyński
a key information from the point of view of effective laser working. UV-Vis
spectroscopy is also widely used in analytical chemistry, e.g., to determine the
concentration of ions, molecules, or functional groups responsible for individual
absorption peaks.
Electron spectroscopy methods [9–12] (XPS—X-ray photoelectron spectroscopy, UPS—ultraviolet photoelectron spectroscopy, or AES—Auger electron
spectroscopy) measure the kinetic energy of electrons emitted from the material as a
result of exposure to high energy ionizing radiation or high energy particles
bombardment. The main difference between XPS and UPS methods is in the atomic
shells which can be studied: The inner shells electrons can be ejected using higher
energy X-rays (frequencies around 10
18 Hz), while valence shells electrons can be
ionized using lower energy ultraviolet light with the frequencies about 10
16 Hz. The
kinetic energy of electrons measured by these methods is equal to the difference
between the energy ht of the used incident radiation and the binding energy
(ionization potential) of the emitted electron and depends strongly on the type of
atom from which the electron was emitted, its oxidation state, and its immediate
environment; whereby it is possible to use these techniques to identify the atoms of
a given element in the material, providing the basis for electron spectroscopy for
chemical analysis (ESCA) developed by Siegbahn et al. [13].
The method directly related to the XPS and UPS spectroscopy is the Auger
electron spectroscopy [11, 14], in which emitted electrons are not the electrons
primary ionized by X-ray or ultraviolet radiation, but the product of secondary
processes, i.e., decay of ionized atoms from excited states to lower energy states
associated with emission of a photon, which can be emitted (and measured by XPS
or UPS) or absorbed by the electron from outer shells, resulting in the emission of
such secondary ionized electron (called the Auger electron). Electron spectroscopy
methods are very important and useful methods to determine energy levels in atoms
and molecules. In the case of solids, they are particularly useful for studying the
local structure of the surface of materials, since due to the relatively low energy of
emitted electrons and their strong dissipation in the material, in practice it is possible to observe only electrons ejected from the surface layer with a thickness of up
to 5 nm.
Even higher energies than those used in electron spectroscopy require processes
of transitions between energy levels of atomic nuclei (around 10
19 Hz). The method
that examines such processes is the Mössbauer spectroscopy [15, 16], based on the
Mössbauer effect (i.e., resonant and recoil-free emission and absorption of c-rays by
atomic nuclei in a solid). In Mössbauer spectroscopy, three types of nuclear
interactions are observed:
• Isomer shift (energy shift of the absorption peak resulting from the modification
of the energy levels of the nucleus by changes in the distribution of electron
density in the atom, due to the changes in the local environment of the atom; this
shift may, e.g., correlate with the electron density at atomic nucleus of the outer
s shells electrons);
4
A. Koleżyński