Showing papers by "Gérard Tourillon published in 1986"

X-ray absorption in dispersive mode: A new spectrometer and a data acquisition system for fast kinetics

Abstract: The photodiode array provided a position sensitive detector for powerful X-ray sources. Then the development of the energy dispersive scheme for the X-ray absorption experiments became realistic. The data acquisition system and elements of optics are discussed. Experiments in transmission mode and in total reflection mode illustrate the dramatic gain in data acquisition time as well as advantages dealing with the focussing optics.

Exafs in dispersive mode, a new tool for studying in situ kinetics : example of electrochemical inclusion of copper species in an organic conductor

Abstract: The mechanisms and t h e k ine t ics f o r t h e e lec t rochemica l i nc lus ion 01 c o p p e r spec ies i n s i d e p o l y 3me thy l t h iophene (an o rgan i c conduct ing p o l y m e r ) have been s tud ied i n s i t u b y d i s p e r s i v e x r a y abso rp t i on spec t roscopy . The EXAFS r e s u l t s compl'ement t h e t h r e e chemica l s tep$ p r e v i o u s l y deduced f r o m XANES and t h e n a t u r e of chemica l bonds formec dur ing the inc lus ions processes a r e then p rec i sed : a fas t cu2'-t cu l+ reduct ion where the CU\" ions a r e complexed by the 0 atoms coming f r o m the dopant used dur ing the po l ymer synthesis (S03CF3)-F i xa t i on of t he new synthet ized C U ' ~ ~ O ~ S on the S atoms of po l y 3methyl th iophene -Growing of ( 1 1 1 ) meta l l i c copper p la te le t s .

INVESTIGATION OF BURRIED INTERFACE (Si3N4/Ga As) BY EXAFS IN TOTAL REFLECTION AND DISPERSIVE MODE

Abstract: To reach a burried interface below the passivating film is often out of the capability of experimental technique. The X-ray absorption, spectroscopy using the total reflection scheme allows such investigation if the deposited film has a lower electronic density than the substrate one. This requirement is fulfilled with Sig N4 on Ga As. Two considered processes leads to interfaces with large differences. PECVD keeps well-defined reflecting surface, while the cathodic reactive sputtering gives rise to an island-type one, this results agree with XPS measurements. Although plasma deposited silicon nitride is widely used to passivate or encapsulate Ga As (100) wafers. little is known about the interfacial chemistrv between Ga As and the insulating laver. x-ray absorption spectroscopy using the total reflection h to tune the glancing angle. The 2inch-long Ga As wafers reflect a 100p-thick beam slice when the glancing angle is set at 0.4 mad. Hence, because of our beam vertical size a loss of intensity by a factor 20 is already achieved compared to the transmission scheme(2). It has been pointed out that optimized data are obtained when the sample orientation is adjusted to about 98-0.9 times the critical angle in order to reduce the contribution of the real part of the index to the EXAFS modulations (3). This residual effect does not affect the periodicity of the oscillations but conclusions drawn from the EXAFS amplitude would be irrelevant. The dispersive configuration concentrates the beam onto a few mm-wide band of the sample but gives our experiment more sensitive to dust or particles on windows, or reflecting surface since it affects locally the beam path and its local intensity. This last point is a concern added by the reflected scheme. An other way to produce "glitches" arises from the perfect cristallinity of the substrate which generates Bragg reflections for specific energies. Finally the dispersive scheme does not include an intrinsic calibration. The energy scale obtained in the preliminary transmission mode is useless. The surface is always slightly tilted wich induces a shift of the energy-pixel number correlation. To overcome this inherent difficulty we always used the reflected beam as a primary beam in which we inserted the homogeneous thin GaAs standard sample. A last but not least need is to know the hypothetical intensity versus photon energy given by a perfect non absorbing surface in order to calculate the absorption. A pratical way to do that is to substitute a platinum-coated float glass to the GaAs sample. Hence the geometry remains unchanged and the 10 profile can be derived. It is obvious that this technique requires mirror of very high quality.