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Chemische Prozesse und Phasenübergänge Vortrag: Fr., 12:10–12:30 F-V65
Coherence experiments with white synchrotron radiation
Tobias Panzner 1 , Wolfram Leitenberger 2 , Gudrun Gleber 1 , Tushar Sant 1 ,
Ullrich Pietsch 1
1 Festkörperphysik, Universität Siegen – 2 Institut für Physik, Universität Potsdam
The third-generation X-ray source BESSYII (Berlin, Germany) provides a certain
portion of coherent x-ray radiation which can be used for static and dynamic speckle
analysis. Since about three years our group follows the concept of using “white”
radiation for coherence experiments. Exploiting the exponentially decaying part of
the BESSYII emission spectrum (critical energy 1 keV) we can use energies between 5
< E < 20 keV with sufficient coherent flux.
Various experiments were performed to test and to measure the coherence properties
at the white-beam bending-magnet beamline (EDR). We measured static speckles
from plane and surface patterend semiconductor and polymer surfaces under grazingincidence
over a wide energy range simultaneous. In this scattering geometry the
Fourier-back transformation is influenced by the incindence spectrum which already
contains features of Fresnel diffraction of the coherent beam at the incident pinhole.
This apparatus function has been measured at the samples site for different incidence
conditions and was simulated in terms of Lommel formalism. Knowing this function
one is able to deconvolute measured reciprocal space maps by the apparatus function
to receive the speckle pattern of the measured surface. On the other hand one can
consider this function as input for reconstruction of the true sample surface.
Using this setup we performed first XCPS studies at polymer surfaces. On time scale
of several 10 seconds we detected the dynamics of molecular movement initiated by
laser light at the surface of light-sensitive azopolymer film. Considering the apparatus
function one can discriminate between static features due to Fresnel scattering from
incident pinhole and dynamic speckles induced by the light. Both show different autocorrelation
function as well. The features can be observed simulataneous over a broad
energy band which help to distinguish between diffusion and not-diffusion controlled
processes.