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SYNCHROTRON RADIATION PLUS PHOTODIODE ARRAY : EXAFS IN DISPERSIVE MODE FOR FAST
MICROANALYSIS
E. Dartyge, A. Flank, A. Fontaine, A. Jucha
To cite this version:
E. Dartyge, A. Flank, A. Fontaine, A. Jucha. SYNCHROTRON RADIATION PLUS PHOTODIODE ARRAY : EXAFS IN DISPERSIVE MODE FOR FAST MICROANALYSIS. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-275-C2-277. �10.1051/jphyscol:1984261�. �jpa-00223975�
JOURNAL DE PHYSIQUE
Colloque C2, suppl6ment au n02, Tome 45, f6vrier 1984 page C2-275
SYNCHROTRON R A D I A T I O N PLUS PHOTODIODE ARRAY : EXAFS I N D I S P E R S I V E MODE FOR F A S T M I C R O A N A L Y S I S
E. ~ a r t ~ ~ e * , A.M. lank**, A. ~ontaine* and A. Jucha L.U.R.E., B a t . 209 C, 91405 Orsay Cedex, & m e
*&boratoire de Physique des SoZides, 91405 &say Cedex, France
**~aboratoire de M6taZZurgie Physique, Avenue du Recteur P-ineau, 86022 Poitiers, France
Resume - L I E X A F S dispersif permet d'obtenir en une seule mesure la totalit6 d'un spectre EXAFS. L'utilisation de barrettes dephotodiode comme detecteur, permet d'utiliser le faisceau intense du rayonnement synchrotron et de reduire ainsi le temps de mesure. Ceci permet des etudes cingtiques comme dans le cas de la pr6-precipitation des alliages Al-Zn.
Abstract-EXAFS in dispersive mode allows one to record simultaneausly the whole EXAFS spectrum.
The high flux of the synchrotron radiation beam is scanned with photodiode array, which yields short integration times. This allows kinetics studies, as for example the clustering of A1 Zn alloys.
Fig. 1 : schematic of the energy dispersive X-ray absorption spectrometer. The angle of incidence i of the primary X-ray beam varies continuously across the surface of the bent mono- chromator - 0 is the Bragg angle, q the focussing distance along the central ray, a is the angle between the surface of the mono- chromator and its reflecting planes - EL and E H are the lowest and highest energy rays.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984261
C2-276 JOURNAL DE PHYSIQUE
EXAFS is a local probe which can be considered as an electronic diffraction performed with an electronic source created out of one particular sort of atom in the studied sample. The new method of collecting EXAFS data in dispersive mode allows one to record simultaneously the whole EXAFS spectrum. This improved efficiency in data collection opens up the possibility of kinetics studies in material science, chemistry an d biophysics.
The principle and characteristics of the method bave been expe- rimented at Stanford (1) (2) and at LURE (3) (4) . We recall that a cylindrically curved monochromator focusses the polychro- matic and quasi parallel synchrotron radiation beam onto the absorbing sample and disperses the beam beyond the sample (fig. 1).
A detector using a cooled photodiode array collects the EXAFS spectrum. Photodiode arrays as detectors are needed since they can handle large counting rates ( l 0 ~ - 1 0 ~ C/S) and can resolve the dispersed beam to high resolution.
a r b i t r a r y u n ~ t~
r
3 1 x e \ number
Fig. 2 : X ray absorption spectra of quenched A1 Zn 6 , 8 at % Zn : a) after 5,5 s annealing time at 300 K
b) after 1145 s annealing time at 300 K
As an example of kinetic study, we show in fig. 2 the EXAFS spectra of one A1 Zn alloy 6 , 8 at % Zn quenched from the homo- genisation temperature with the procedure explained in (5), and annealed at 300 K for 5,5 s and 1145 S. The experiments were realised at LURE on the beamline D11 dedicated to small angle scattering experiments. The monochromator was a Si (111).
The data were recorded with a RL1024SFX RETICON photodiode array. This detector has a X-ray phosphor coating the input side of the fiber optic face plate. The detector was operated at -4OoC.The integration time was 100 ms. The calibration energy was obtained recording with the same device the known EXAFS
spectrum of pure Zn.
Fig. 3 shows the Fourier transforms of the spectra of Fig. 2.
One can observe the drastic change in the first peak due to the
i n c r e a s e o f t h e n u m b e r o f Zn a t o m s i n t h e f i r s t s h e l l o f n e i g h b o u r s a r o u n d o n e Zn a t o m d u r i n g t h e a n n e a l i n g . T h e n u m b e r o f Zn a n d A1 a t o m s i n t h e f i r s t s h e l l , a n d t h e i r d i s t a n c e t o t h e c e n t r a l a t o m c a n b e e a s i l y o b t a i n e d f r o m t h i s e x p e r i m e n t ( 5 ) . T h e
s h o r t t i m e o f c o l l e c t i n g t h e d a t a ( 2 X 1 0 0 ms) w i l l a l l o w a p r e c i s e s t u d y o f t h e f i r s t s t a g e s o f c l u s t e r i n g i n t h i s c l a s s o f a l l o y s .
F i g . 3 : F o u r i e r t r a n s f o r m o f t h e EXAFS s p e c t r a o f A 1 Zn 6 , 8 a t % Zn a ) a f t e r 5 , 5 s a n n e a l i n g t i m e a t 3 0 0 K
b ) a f t e r 1 1 4 5 s a n n e a l i n g t i m e a t 3 0 0 K
REFERENCES
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