AbstracL We present the 2p &,a) absorption spectra of first-mw transition metal ions in tetrahedral and octahedral clystal field symmetly. These have been calculated using a localized desaiption for the 3d" Lo 2p53d"+' excitation including electrostatic and spin-xbit interactions. The spectra are significantly different from those already presented where the 3d spin-orbit interaction was neglected. The speclral shape provider a valence-and symmctly-selective probe. Whereas it changer gradually with the cryftal field, abrupt changes in the spectra are indicative of high-spin to lowapin transitions. These spin transitions are accompanied by a stmng decrease in the Zp branching ratio. The calculated spectra provide a basis for the use ut k , s absorption spectrosmpy in materials science and biological science. The limitations of these calculations and the use of configuration interaction are discussed.
By employing polarization-and temperature-dependent near-edge x-ray-absorption fine structure ͑NEXAFS͒ studies, we show that vertically aligned carbon nanotubes when subjected to low-pressure radio-frequency ͑rf͒ glow discharge can easily be doped with nitrogen atoms at predominantly graphitelike substitutional sites and at the same time preserve their vertical alignment in contrast to commonly used wet chemical functionalization methods. The O K edge NEXAFS spectra and angle-dependent x-ray phoelectron spectroscopy measurements established the presence of a significant amount of oxygen containing functional groups localized at the outer part of the walls. The amount of oxygen adsorbed on the carbon nanotubes is dependent on the introduction of nitrogen sites and exposed edge plane defects generated by plasma N treatment. Thermal gravimetric analysis measurements revealed a lower decomposition temperature for the plasma treated carbon nanotubes, which has its origin in the presence of a large fraction of active sites induced by rf glow discharge plasma treatment that accelerates the oxidation rate of N-doped carbon nanotubes. Our results indicate that rf low-pressure glowdischarge-mediated doping of nanotubes is a promising route to control the electronic structure of nanotubes and their reactivity due to introduction of active site defects.
The present study aims to understand the reasons for the visual differences of black gloss pottery found in northern Etruria. The results obtained by conventional (scanning electron microscope, electron microprobe) and synchrotron (X‐ray diffraction, X‐ray absorption spectroscopy) techniques indicate that the thickness, porosity or chemical composition of the different types of gloss cannot be used as the principal distinguishing factor. The size of quartz or feldspar crystals may well be a critical factor responsible for the matt effect in some samples, while the range of mixtures of iron compounds indicated by XRD and XAS could be the reason for differences in colour and reflectivity. The Fe L‐edge XAS results in particular show that a correlation does exist between the oxidation state characteristics and the visual appearance. The Si, Fe and Al contents seem to further discriminate the different types of gloss that have differing visual appearances.
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