A. Jucha

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.

X-ray absorption spectroscopy in dispersive mode and by total reflection

Abstract The association of the total reflection scheme with the dispersive mode allows one to record in short time the EXAFS and XANES spectra of the first 30 A of a surface. In situ time resolved observations of the surface modifications under chemical or electrochemical treatments are thus accessible. This promising technique is illustrated through two examples: (i) the thermal oxidation of a metallic copper surface and (ii) the electrochemical inclusion of Cu + ions within a 5000 A organic conducting polymer (poly-3-methylthiophene) electrochemically deposited on a platinum surface.

Fast and adjustable-resolution grazing-incidence x-ray liquid surface diffraction

We developed a configuration using a two-dimensional detector for grazing incidence x-ray diffraction on Langmuir monolayers and, more generally, for surface diffraction on two-dimensional powders. Compared to the classical setup using a linear detector combined with Soller slits, the acquisition time is reduced by an order of magnitude (from more than 1 h to a few minutes) using the same x-ray source (synchrotron bending magnet) with a comparable signal to noise ratio. Moreover, experimental resolution can be adjusted by varying a vertical slit (horizontal gap) and, for small values of the gap, better resolution can be achieved compared to the one obtained with the Soller slits and linear detector.

H10:: A materials and high temperature beamline at LURE/DCI

A new beamline dedicated to materials and high temperature studies, combining X-ray scattering and X-ray absorption measurements, is now in operation at LURE/DCI. The source is a bending magnet and the energy range of the beamline is 4–20 keV. Here we describe the beamline and, since a part of it (mainly the optical part) should move to the 3rd generation SOLEIL storage ring, we also present the results of a ray-tracing analysis taking into account the characteristics of the two sources (DCI and SOLEIL). Examples of experiments achieved on the beamline are shown, in particular scattering experiments on liquid Al2O3 at 22508C and absorption spectroscopy at the Ca K edge. # 2001 Elsevier Science B.V. All rights reserved.

Directly illuminated photodiode array as a position sensitive detector for synchrotron X-ray radiation

Abstract A system of a cooled directly illuminated photodiode array of 1024 pixels 25 μm apart is described. The spatial resolution has been measured and is better than 50 μm (2 pixels). The dynamic range is shown to be larger than four orders of magnitude. The downstream setup allows us to record 60 spectra before transfer to a mass storage. The radiation damage observed after irradiation is crudely estimated to be due to 10 15 −10 16 10-keV photons. Attempts to cure it using UV illumination or thermal annealing have been persued.

High-Pressure Energy Dispersive X-Ray Absorption of EuO up to 300 kbar

The cubic insulating ferromagnet EuO (TC = 69 K) is often considered as an ideal Heisenberg ferromagnet and is the subject of extensive investigations, including numerous high-pressure studies /1,2,3/. From the pressure-volume relationship, obtained by high-pressure x-ray diffraction, a pressure induced valence change from Eu2+ towards Eu3+ at 300 kbar was concluded /2/.

Time-Resolved EXAFS

When synchrotron radiation became available it has been possible to reduce the data collection time of one EXAFS spectrum from 2 or 3 weeks using the bremsstrahlung of a conventional generator down to a few minutes when using the white beam provided by a magnet of storage ring.