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HIGH-TEMPERATURE OXIDATION OF ONE-COMPONENT AND 2-COMPONENT METALLIC SYSTEMS STUDIED BY IN-SITU X-RAY-ABSORPTION SPECTROSCOPY
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Do we have a probe for the initial stages of solid state reactions?
No full textThe aim of this work is to show that ReflEXAFS can be used as a tool for investigating the initial stages of solid state reactions, when local chemical equilibrium is not yet attained at the interfaces. A very classical solid state reaction, i.e. the formation of Ni-Al spinel starting from the parent oxides (NiO + Al2O3 → NiAl2O4) has been investigated by monitoring with Ni-K edge ReflEXAFS the time evolution of the local chemical environment of Ni in a reacting NiO thin layer. At temperatures above 1000°C, a progressive evolution from an NiO environment to a spinel environment has been obtained with increasing firing times. At lower temperatures (≅ 930°C) the NiO film does not react but undergoes a structural rearrangement, which is seemingly related to the process by which local chemical equilibrium is attained at the interface
Electron spectroscopy analysis on NbN to grow and characterize NbN/AlN/NbN Josephson junction
No full textThree layers, NbN based Josephson junction, has been growth by RF and by DC sputtering within the
constrain required by the photolithography technology. An interesting superconducting film with critical
temperature of Tc = 14 K, well above the temperature of the commercial cryocooler, has been obtained
reducing sputtering power and finding a proper N2 concentration in the gas mixture. The search of the
new sputtering parameters has been obtained with the help of electron spectroscopy and X-ray diffraction
analysis
The refiEXAFS station at the GILDA beamline (BM08) of ESRF
No full textThe experimental station for measuring X-ray absorption spectra in total reflection geometry operative at the GILDA CRG beamline of ESRF is described. The main features of the station are shown, namely: the possibility of detecting very small signals from thin (a few ML) samples, of depositing thin films under controlled conditions and thermal treating the samples in order to study dynamical processes. Case studies are reported in order to show the performances of the apparatus
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The valence and speciation of sulphur in glasses by X-ray absorption spectroscopy
No full textThe geochemical behavior of sulfur in magmas depends strongly on the oxidation state of sulfur, but this is not easily determined by standard analytical methods. We have measured XANES absorption spectra at the sulfur K-edge and have found that such measurements are useful to characterize the oxidation state and speciation of sulfur in silicate glasses of geological relevance. Measured spectra of a set of reference minerals show the effects of different oxidation states and coordination numbers of sulfur; there is a large shift in energy (~10-12 eV) of the sulfur K-edge between S2- and S6+. This large and easily detectable difference makes possible the measurement of the valence of sulfur in unknown samples by measuring the shift in energy of the absorption edge. This approach is applicable to both crystalline and glassy materials, and useful results have been obtained on samples with as little as 450 ppm S. We have used XANES measurements to characterize oxidation state and speciation of sulfur in a set of natural and synthetic sulfur-bearing glasses. The samples cover a range of composition from basaltic to almost rhyolitic, and some were synthesized over a range of pressure, temperature and oxygen fugacity; glass S content varies between 450 and 3000 ppm. XANES analyses, carried out in fluorescence mode at LURE, allowed determination of the sulfur oxidation state in all of the samples and clearly show that some samples contain a mixture of S2- and S6+; no other sulfur species were observed. Quantitative determination of the abundance of sulfide and sulfate shows good agreement with independent measurements based on electron-microprobe determination of the wavelength shift of sulfur Kα X-rays
Temperature modification of the Nb oxidation at the Nb/Al interface studied by reflEXAFS
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