The uppermost atomic layers of a substance determine what it looks like, how it reacts and what it can be used for.
At surfaces and ot he interfaces, where different phases are in contact with each other, a number of important physical and
chemical processes take place: physe transitions like growth, melting, dissolving, evaporation, mechanical and chemical
attack like abrasion, corrosion, passivation and chemical reaction, catalysis. This is due to the fact that an atom or molecule that
is situated at an interface has a different atomic surrounding than one that is located in the bulk. Also nanomaterials behave
different that solids with more volume and often, nanostructures that are technologically interesting are located at surfaces.
X-ray scattering is a nearly ideal tool to study for example mechanisms of crystal growth. The
interplay of the X-rays with matter is of great importance, since it allows a destruction free
measurement and a simple mathematical analysis, because multiple scattering can be neglected.
To look at thin films and surfaces, we need synchrotron radiation to reach the needed signal strength
in spite of low interactions. By varying the wave angle the interaction depth can be changed from
some Ångströms to many micrometers, so that both extremely surface sensitive measurements
and the analysis of thick stacks of layers are possible.
Many important physical, chemical or biological processes take place at buried interfaces , i.e.
interfaces that are conceiled under a solid or fluid layer and there are not accessible by surface sensitive methods.
For example, the function of many technologically relevant electronic components is based on processes at buried interfaces,
e.g. in semiconductor-structures like solar cells or illuminating diodes or in magnetic border layer systems.
While the structure studies of bureid layers have reached a high development status, so far only in adequate single cases
spectroscopical studies of such interfaces were done. Those studies are of central interest for the understanding
of the chemical and electronic properties. An important contribution comes from X-ray emission spectroscopy (XES) with
soft X-rays (< 1 keV): since the modern synchrotron radiation sources with hight brilliance are available, it is possible
to study the electronic structure of bulk samples and buried layers within specific to the atom and the chemical surroundings with
high energy resolution.
An advantage of synchrotron radiation compared to imaging methods is that it alow teh determinataion of mean interfaces properties over large areas.
Yet, also extremely small structures can be studied, as for example "quantum dots",
tiny clusters of atoms which can be observed and also manipulated. One possible application would be to use quantum
dots as minute lasers which emit colours that cannot be produced in other ways. Research in nanotechnology certainly
looks set to revolutionise consumer electronics of the future, paving the way for such things as quantum computers and
flexible ultra-flat screens.
Sources: Kleine Enzyklopädie Physik, Verlag Harri Deutsch / SNI2006, Wolfgang Braun / Brochure "European Research in Grenoble" / KFS-Broschüre "Forschung mit Synchrotronstrahlung in Deutschland"