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

Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P46
Time-resolved X-ray absorption spectroscopy - recent advances and new
applications
Dirk Lützenkirchen-Hecht 1 , Bernd Griesebock 1 , Ronald Frahm 1
1 Fachbereich C - Experimentalphysik, Bergische Universität Wuppertal, Gauß-Str. 20,
42097 Wuppertal
Time-resolved X-ray absorption spectroscopy (QEXAFS) yields structural information
during fast chemical decomposition reactions, thin film deposition, solid-state reactions,
phase transformations etc. This presentation will outline the technical developments
of the QEXAFS technique, its current state and the most challenging results. More
specifically, we will present results obtained using a cam-driven oscillating doublecrystal
monochromator (DCM) with a channel-cut crystal. This DCM has been used
at various synchrotron radiation sources worldwide, e.g. at HASYLAB, the ESRF,
LURE, ANKA and the APS. Depending on the available photon flux and sample
quality, repetition rates of about 100 Hz can be realized for XANES measurements,
while the acquisition of full EXAFS spectra with a scan range of more than 1 keV
and a repetition rate of 10 Hz are feasible. Using cryogenic cooling, the silicon crystal
can cope with the full heat load from third generation undulator sources. Excellent
data quality can be obtained. Since a fast sequential energy scanning technique is
used, the detection of fluorescence radiation or surface sensitive techniques such as
reflection mode EXAFS can be applied, and a reference sample can be monitored
simultaneously with each measurement. This permits to detect even very small changes
of the edge position - and thus the chemical valency of the species of interest - with a
high accuracy. XANES-microtomography with a lateral resolution in the micrometerscale
becomes feasible by combining the fast scanning monochromator with refractive
X-ray lenses for beam focusing. Furthermore, the combination of time-resolved Xray
absorption spectroscopy (Quick-XANES) with additional techniques such as UV-
Vis, Raman-spetroscopy or differential scanning calorimetry (DSC) is feasible. We
will different applications of the new technique ranging from solution chemistry to
heterogeneous catalysis and biological sample systems.