Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P45
Combining non-specular X-ray scattering and X-ray absorption spectroscopy
- A new method for surface science
Dirk Lützenkirchen-Hecht 1 , Patrick Keil 2 , Ronald Frahm 1
1 Fachbereich C - Experimentalphysik, Bergische Universität Wuppertal, Gauß-Str. 20,
42097 Wuppertal – 2 Max-Planck Institut für Eisenforschung - Adhesion and Thin
Films, Max-Planck-Str. 1, 40237 Düsseldorf
The atomic structure and the chemical composition of buried interfaces is of high interest
for many applications e.g. in multilayered samples such as oxidized metals, optic
and microelectronic devices. Due to the various functions of modern materials, nondestructive
testing methods are highly desirable. We will show that the combination
of grazing incidence non-specular X-ray scattering with X-ray absorption spectroscopy
enables surface-sensitive structural investigations yielding many details of thin films
or multilayered systems. More specifically, investigations of buried interaces are are
feasible.
Our new approach makes use of the distinct off-specularly scattered intensities which
appear for grazing angles in the vicinity of the critical angle of total reflection. Extensive
work in the past has shown that the intensity of this so-called Yoneda-peak is
related to lateral surface inhomo-geneities such as roughness, and that a quantitative
calculation is possible in many cases using sophisticated mathematical models such as
the distorted wave born approximation. Since the angular position of the Yoneda-peak
is strongly correlated with the density of the X-ray scattering materials, different interfaces
can be selected by the choice of the scattering angle. Therefore, by measuring
the X-ray absorption fine structure for given, well defined incidence and exit angles, it
is possible to study the atomic short range order and the chemical state of a chosen
element.
By analyzing the spectra measured for well defined model systems such as noble
metal thin films, we will first show that a quantitative description of the measured
data is possible. In a second step, structural investigations of different samples will
be presented. In the case of oxidized copper, a detailed insight into the structure of
the multilayered oxide film is accessible. For metallic double layers (copper on gold)
prepared by evaporation or sputtering, the Cu atoms at the Cu-air (vacuum)-interface
can be separated from those in the inner Cu-Au interface in an unambiguous way.