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The effect of temperature on the structure of an Ir/γ-Al2O3 catalyst has been investigated. It was found that the assumption of a Gaussian Debye–Waller factor was valid for a temperature up to at least 573 K, for both the Ir–Ir and the Ir–O contributions. Theoretical references were generated using FEFF7 for the Ir–Ir and the Ir–O contributions. From the results of the EXAFS analysis, we conclude that the inter-atomic potential of very small particles forces the metal atoms to move more harmonically. Consequently the Einstein temperature, which indicates the temperature at which anharmonicity becomes important, increases. The results show that at reaction temperatures it is possible to obtain information with XAFS spectroscopy about first the structure of supported small noble metal particles and second the structure of the metal–support interface.

Both double-electron excitation (DEE) and atomic XAFS (AXAFS) contributions are shown to be present in L23 x-ray absorption spectra of Pt foil and Na2Pt(OH)6. In the Fourier transform of the spectra, the DEE feature appears at lower R values than the AXAFS feature. A background subtraction procedure is developed that leaves the DEE contribution in the background and the AXAFS in the oscillatory part of the spectrum. The separation of the DEE and the AXAFS contributions is possible only when using a cubic spline function routine in which the smoothing parameter can be continuously adjusted.

The physical principles of XAFS spectroscopy are given at a sufficiently basic level to enable scientists working in the field of catalysis to critically evaluate articles dealing with XAFS studies on catalytic materials. The described data-analysis methods provide the basic tools for studying the electronic and structural properties of supported metal, metal–oxide or metal–sulfide catalysts. These methods include (a) fitting in R-space, (b) application of the difference file technique and (c) control of the fit procedure with k 1 and k 3 weighting with the help of phase- and amplitude-corrected Fourier transforms.

The physical principles of atomic XAFS (AXAFS) are presented along with important details on how to isolate the AXAFS contribution from the experimental XAFS data. Intuitive illustrations are given showing how various interactions of the absorber atom with its neighbours influence the AXAFS contribution. Hydrogen chemisorbed on the surface of the supported metal particles is shown to have a strong influence on the amplitude of the Fourier transform AXAFS peak. The effect of the support (with different amounts and types of charge compensating ions (H+, K+), different Si/Al ratio and extra-framework Al) on the experimental AXAFS spectra of Pt dispersed in zeolites (LTL,Y) and on flat supports (Al2O3–SiO2, MgO–Al2O3) are summarised. It is shown that the essence of the metal–support interaction, as revealed in the AXAFS, is a shift in the ionisation potential of the valence d-orbital electrons brought about by the polarisation induced primarily by the changing charge on the support oxygen atoms.

EXAFS measurements on RbBr at the Br absorption edge and different temperatures were carried out. Conventional analysis of the data using the Daresbury EXCURV92 code shows with increasing temperature a decrease in nearest neighbour distance. Also large differences are found in the coordination numbers for k and k' weighted EXAFS with increasing temperature. Using cumulant expansion when fitting the data results in a small increase in nearest neighbour distance with temperature, as expected from thermal data.

This paper was published as Journal de Physique IV, 1997, 7 (C2), pp. 151-152. It is available from http://jp4.journaldephysique.org/index.php?option=article&access=doi&doi=10.1051/jp4/1997146. Doi: 10.1051/jp4/1997146

Using a newly developed reflectometer we have measured the reflectivity of crystalline silicon and SiO x coated float glass at the silicon K absorption edge. The reflectometer can be used without the need for ultra high vacuum. The critical angle of total reflection was determined and the reflection as function of the energy was measured below the critical angle. EXAFS analysis of the data reveals the oxygen content in the samples, and the local structure around the silicon absorbers. The measurements show the strength of ReflEXAFS as a technique to study surfaces under “real” conditions.

The problems inherent in the fabrication of short period multilayer mirrors are discussed and results of the synthesis of multilayer structures with nanometer period are presented. The shortest period observed is 13 A for WSi and WB 4 C sputtered multilayers. Measurements of near normal incidence reflectivity at λ = 31–32A are presented for WSc multilayers with a period approximately 16 A. The measured reflectivity reaches a maximum of 3.3% and is in good agreement with theoretical modeling after the inclusion of interfacial roughness.

In this paper we discuss two techniques to optimize the quality of multilayer x-ray mirrors, namely optimization of the temperature of the substrates during deposition and ion-bombardment of the layers. We produced Mo/Si multilayers applying both methods and present the effect on the near normal incidence reflectivity for λ = 13–14 nm radiation. Furthermore an analysis of the homogeneity of the deposited layers is given.

The X-ray emission from laser-produced plasmas at an X-ray wavelength of approximately 10.4 nm was measured for Al and Gd target materials. The laser power density on the target surface was varied between 1.5 × 1010 and 3 × 1012 W/cm2 to obtain different electron temperatures. The output from the plasma was measured using an X-ray reflecting Pd-C multilayer coating as a wavelength-selective element and a diamond photoconductive detector. The emission at 10.4 nm is strongest at the low end of the power density range investigated. A strong increase is found for Al targets due to a contribution of line radiation, which is not present in the Gd plasmas. The measured conversion efficiency for Al plasmas was (4.5 ± 1)% in a 3% bandwidth at an X-ray wavelength of 10.4 nm.

Using a newly developed reflectometer we have measured the reflectivity at the silicon [ital K] edge for different silicon compounds. Combining these measurements with silicon [ital L] edge reflectivity measurements carried out on a different reflectometer we determined the binding energy of core excitons at the [ital L] edge. The results show that it is possible to carry out reflectivity measurements with the resolution necessary for the determination of the exciton parameters. Comparison with literature values shows that a rigid Kramers--Kronig analysis is not needed when the angle of incidence is well below the critical angle of total external reflection.

This study focuses on explaining differences in soft X-ray reflectivity observed for Mo/Si multilayers produced by e-beam evaporation with two different additional methods: ion etching of the Si layer and optimization of the substrate temperature during deposition. A 32-period multilayer made with ion etching has a near normal incidence reflectivity of 50%, while the one made at an optimum deposition temperature shows only 41%. The values for the interface roughness or layer thickness errors obtained from the analysis of small angle reflectivity measurements cannot explain this difference, but a different morphology of the Si and Mo layers could. Extended X-ray absorption fine structure (EXAFS) experiments have been carried out at the Si-K and the Mo-K edge to obtain information on the multilayer structure and chemical composition. The results of these EXAFS measurements on the two types of multilayers indicate that both the Si and the Mo have an amorphous structure and that no Mo-Si compounds are formed at the interfaces. However, it is found that multilayers made with ion etching have a reduced fraction of oxygen (less than or equal to 0.5%) in the Si layer compared to layers produced without etching (4.7%). The latter fraction of oxygen, originating from the background gas in the deposition system, results in higher absorption of soft X-ray radiation and therefore affects the near normal incidence reflectivity. Although both the Si and Mo layers produced with the three different deposition methods are amorphous, some structural differences have been found using the EXAFS analysis.

The increasing reflectivity of multilayer mirrors has made the use of reflective soft x-ray optical systems, e.g. in soft x-ray microscopy and soft x-ray projection lithography [1,2] possible. However, the use of multi-mirror systems [3] in industrial applications can only be successful if such a system has sufficient throughput. It is therefore necessary to optimize the reflectivity to the highest value possible.

A new method for the determination of the absolute brightness of pointlike soft-x-ray sources is proposed, and an example of its application is shown at a laser-plasma source for a wavelength band from 0.8 to similar to 1.7 nm.