Threshold Al KLL Auger spectra of oxidized aluminium foils

Threshold Al KLL Auger electron spectroscopy and K‐edge x‐ray absorption fine structure spectroscopy have been used to examine technical purity (99.5%) aluminium foil before and after chemical treatment that altered the thickness and degree of hydroxylation of the oxidized layer. Comprehensive surface chemical characterization was effected by means of monochromatized Al Kα‐excited photoelectron spectroscopy. Threshold Al KL_{2, 3}L_{2, 3} spectra were obtained for three of the foils investigated and these spectra were in broad agreement with those observed previously for pure Al foil. The relative intensities of the spectral components for two of the foils were clearly consistent with the previously proposed assignment of the resonantly enhanced Auger component, situated between those arising from the metal and Al(III) oxide, to a thin interfacial layer. The threshold Auger spectra from the aluminium foil bearing the thickest and most hydroxylated oxidized layer were not obviously consistent with the interfacial layer model but O K‐edge spectra revealed that this surface layer was fundamentally different from the others and could have had a greater interfacial surface area. Copyright © 2003 John Wiley & Sons, Ltd.     

Characterization of aluminum–organic‐stabilized platinum–colloid networks with electron and photon spectroscopies

We have measured and interpreted the ultraviolet (HeI) and X‐ray photoelectron spectra and the metastable impact electron spectra (MIES) from aluminum–organic‐stabilized platinum–colloids and colloid networks, deposited on silicon substrates and characterized by X‐ray photoelectron spectroscopy, scanning Auger electron microscopy and transmission electron microscopy. MIES, in particular, gives information on the electronic structure of the spacer molecules interconnecting the colloids. In addition, changes in the electronic structure of the platinum clusters that are induced by different spacer molecules were identified by means of X‐ray absorption near‐edge structure measurements at the platinum L_III‐edge of these materials. This combination of techniques was also employed to follow the chemical changes that occur upon heating of the network in situ. It turns out that the thermal decomposition of the network is driven by the disintegration of the spacer molecules. Moreover, less sintering of the colloidal particles occurs in the networked systems than in unconnected particles. Most of the networked platinum–particles are still present in their original shape even after the destruction of spacer molecules. This observation could be linked to the encapsulation of these platinum particles into an (Al? O) protecting shell. Copyright © 2003 John Wiley & Sons, Ltd.     

X‐ray absorption study of the local structure at the NiO/oxide interfaces

This work reports an X‐ray absorption near‐edge structure (XANES) spectroscopy study at the Ni K‐edge in the early stages of growth of NiO on non‐ordered SiO₂, Al₂O₃ and MgO thin films substrates. Two different coverages of NiO on the substrates have been studied. The analysis of the XANES region shows that for high coverages (80 Eq‐ML) the spectra are similar to that of bulk NiO, being identical for all substrates. In contrast, for low coverages (1 Eq‐ML) the spectra differ from that of large coverages indicating that the local order around Ni is limited to the first two coordination shells. In addition, the results also suggest the formation of cross‐linking bonds Ni—O—M (M = Si, Al, Mg) at the interface.     

Magnesium K‐edge XANES spectroscopy of geological standards

Magnesium K‐edge X‐ray absorption near‐edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg‐bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.     

Observation of phase transition of cesium manganese hexacyanoferrates by X-ray absorption spectroscopy

Cesium manganese hexacyanoferrates exhibit an interesting phenomenon of temperature-induced phase transition accompanied by a variation in the magnetic susceptibility. We observed the variation in the electronic state of Mn during the phase transition by using X-ray absorption spectroscopy. The results of the analyses showed that the content ratio of Fe^II-CN-Mn^III and Fe^III-CN-Mn^II systematically varied during the phase transition. However, the ratio of Fe^II-CN-Mn^II remained constant at almost all temperatures. These results suggest that the charge transfer between Fe and Mn ions in the Fe^III-CN-Mn^II or the Fe^II-CN-Mn^III bond produces the phase transition.     

Structural investigations of tungsten silver phosphate glasses by solid state NMR, vibrational and X-ray absorption near edge spectroscopies

Glasses were prepared in the pseudo-binary system (1 − x)AgPO₃-xWO₃ (0≤ × ≤ 0.6 mol%). The structural evolution of the vitreous network was studied as a function of composition by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), Raman scattering, high resolution ³¹P solid state NMR and XANES at the W-L₁ absorption edge. For compositions with x ranging from 0 to 0.5 a pronounced increase in the glass transition temperature is observed, suggesting a significant increase in the glass network connectivity. At the same time Raman spectra indicate that tungsten atoms are linked to non-bridging oxygen atoms (W-O- or W=O bonded species) whereas the ³¹P MAS-NMR spectra indicate the successive formation of new P-O-W linkages. The formation of some anionic tungsten sites (if these are revealed by the presence of W-O terminal bonds) implies an increase in the average degree of polymerization of the phosphate network, which is consistent with the compositional evolution of the ³¹P MAS-NMR spectra at low x values. For higher x-values, the Raman spectra indicate the presence of W-O-W linkages. W-L₁ XANES data indicate that at least 90% of tungsten atoms are octahedrally coordinated.     

Identification of minority compounds in natural ilmenites by X-ray absorption spectroscopy

Natural ilmenites are used all over the world as raw materials in white pigment (TiO₂) production. Besides the FeTiO₃ in the raw material many other compounds are present. The chemical compounds based on the minority elements influence quality of the final product and are difficult to identify. The knowledge about chemical bonding of the minor elements enables to properly adjust chemical reactions during production processes and to improve quality of the final product. In this paper the X-ray absorption spectroscopy (XAS) identification of the chemical compounds formed by Mg, Mn and Cr in natural ilmenites originating from different places is presented.     

EXAFS and XANES Studies on 3d Transition Metal Intercalation Compounds M x TiS2

Abstract

EXAFS and XANES spectra of Ti K-edge have been measured for 3d transition metal intercalation compounds M _x TiS₂ (M = Mn, Fe, Co and Ni; x ≤ 0.33). We have found that the interatomic distance between Ti and the first nearest neighbor S atoms, R(Ti-S), increases with the guest concentration x. The variation in XANES spectra with x reveals the reduction of the valence state of Ti atoms upon intercalation of M. From these results as well as the M K-edge EXAFS data studied previously, we have proposed a simple model on the local structure of M _x TiS₂ to reproduce the observed values of R(Ti-S) by averaging local shift of S atoms caused by intercalation.     

X-ray absorption study of Cu,Zn SOD under high pressure

Abstract

We have investigated Cu, Zn Superoxide Dismutase (Cu, Zn SOD) metal sites at high pressure using X-ray absorption. XAS (X-ray Absorption Spectroscopy) gives information on local structure and it is particularly suited to metal site investigation. To the best of our knowledge, this is the first time that protein conformational states have been investigated using the high pressure XAS technique. Cu, Zn SOD catalyses the dismutation of toxic oxygen radicals produced in cells; this reaction occurs at the copper metal site. Structural changes around the copper, induced by pressure, can be directly related to protein substates. Their characterisation is thus important in the understanding of protein activity.

The high-pressure device was a Paris-Edinburgh large volume cell.

Experiments were performed on lyophilised Cu, Zn SOD between 0 and 48 kbar at the copper and zinc K-edges. The two metal local atomic environments have a different behaviour as pressure increases: copper exhibits a more flexible environment; on the contrary, zinc shows small structural modifications. We have identified a state, formed between 3 and 8 kbar, which is stable up to 48 kbar.