100 lines
5.1 KiB
ReStructuredText
100 lines
5.1 KiB
ReStructuredText
############
|
||
Introduction
|
||
############
|
||
|
||
Spectroscopies are among the most widely used techniques to study the physical
|
||
and chemical properties of materials. They are now extensively present in many
|
||
fields of science such as physics, chemistry or biology. The term
|
||
“spectroscopy” which was still characterizing the study of light by means of a
|
||
prism in the 19th century, has now, since the advent of quantum theory, a much
|
||
wider meaning. Indeed, according to the 15th edition of The New Encyclopaedia
|
||
Britannica, “spectroscopy is the study of the absorption and emission of light
|
||
and other radiation, as related to the wavelength of the radiation”. If we add
|
||
scattering to the two previous physical processes, the quantum nature of
|
||
particles makes this definition cover most types of experiment that can be
|
||
performed nowadays. Such a typical experiment is sketched below. It should
|
||
be noted that the incoming and outgoing particles are not necessarily the same.
|
||
When they are of an identical nature, the corresponding technique can be
|
||
performed either in the reflection or in the transmission mode.
|
||
|
||
.. figure:: intro_fig1.png
|
||
:align: center
|
||
:width: 50%
|
||
|
||
Typical spectroscopic experiment
|
||
|
||
The idea behind these spectroscopies is that information about the sample can
|
||
be obtained from the analysis of the outgoing particles. Depending on the type
|
||
of spectroscopy, this information can be related to the crystallographic
|
||
structure, to the electronic structure or to the magnetic structure of the
|
||
sample. Or it can be about a reaction that takes place within the sample. With
|
||
this in mind, the type and energy of the detected particles will directly
|
||
determine the region of the sample from which this information can be traced
|
||
back, and therefore the sensitivity of the technique to the bulk or the
|
||
surface. For instance, low-energy electrons or ions will not travel much more
|
||
than ten interatomic distances in a solid while electromagnetic radiations will
|
||
be able to emerge from much deeper layers. In diffraction techniques using
|
||
significantly penetrating particles, surface sensitivity can nevertheless be
|
||
achieved with grazing incidence angles. Note also that the counterpart to
|
||
detecting particles with a small mean free path is the necessity to work under
|
||
ultra high vacuum conditions so that the outgoing particles can effectively
|
||
reach the detector. The figure below gives the variation of the electron mean free path
|
||
:math:`\lambda_e` in solids as a function of the electron kinetic energy. We see
|
||
clearly here that in the range 10–1000 eV, electrons coming from within a
|
||
sample do not originate from much deeper than 5 to 20 Angströms.
|
||
As a consequence, spectroscopies detecting
|
||
electrons in this energy range will be essentially sensitive to the surface structure
|
||
as the particle detected will carry information from the very topmost
|
||
layers.
|
||
|
||
.. figure:: intro_fig2.png
|
||
:align: center
|
||
:width: 80%
|
||
|
||
The electron mean free path as a function of the energy
|
||
|
||
Although, as we have just seen, many techniques can provide information
|
||
on a sample and its surface (if any), we will mainly restrict ourselves here
|
||
to some of them specifically related to synchrotron radiation: x-ray spectroscopies.
|
||
X-ray spectroscopies are characterized by the fact that the incoming
|
||
beam is composed of photons in the range of about 100 eV to 10 keV. Higher
|
||
energies, in the :math:`\gamma`-ray region, will not be considered here as in this latter range
|
||
photons will be scattered significantly not only by the electrons but also by
|
||
the nuclei [2] giving rise to entirely different spectroscopies such as Mössbauer
|
||
spectroscopy. The next, taken from [3], gives a sketch of the electromagnetic
|
||
spectrum with some common photon sources and the spectroscopies corresponding
|
||
to the various energy ranges.
|
||
|
||
.. figure:: intro_fig3.png
|
||
:align: center
|
||
:width: 70%
|
||
|
||
The electromagnetic spectrum, along with the common photon sources and
|
||
some spectroscopies based on photons.
|
||
|
||
|
||
.. seealso::
|
||
|
||
*This introduction is taken from:*
|
||
|
||
X-ray and Electron Spectroscopies: An Introduction
|
||
Didier Sébilleau, Lect. Notes Phys. **697**, p15–57 (2006)
|
||
`[doi] <http://link.springer.com/chapter/10.1007/3-540-33242-1_2>`__
|
||
|
||
*For a more complete theoretical background about multiple scattering, see (and references herein):*
|
||
|
||
Multiple-scattering approach with complex potential in the interpretation of electron and photon spectroscopies
|
||
D. Sebilleau, R. Gunnella, Z-Y Wu, S Di Matteo and C. R. Natoli,
|
||
J. Phys.: Condens. Matter **18**, R175-228 (2006)
|
||
`[doi] <https://doi.org/10.1088/0953-8984/18/9/R01>`__
|
||
|
||
*For a description of the MsSpec code package, see:*
|
||
|
||
MsSpec-1.0: A multiple scattering package for electron spectroscopies in material science
|
||
D. Sébilleau, C. R. Natoli, G. M.Gavaza, H. Zhao, F. Da Pieve and K. Hatada,
|
||
Comput. Phys. Commun., **182** (12), p2567-2579 (2011)
|
||
`[doi] <https://doi.org/10.1016/j.cpc.2011.07.012>`__
|
||
|
||
|
||
|