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Extended energy loss fine structures (EELFS) above the carbon K-edge in CF4 studied at different momentum transfer
No full textAtomic bonding and thermodynamic properties of pseudo-binary semiconducting alloys
No full textThe short-range order of the Cd1-xZnxTe, Hg1-xCdxTe and HgSexTe1-x alloys has been investigated with EXAFS measurements, and a bi-modal distribution of nearest-neighbour bond lengths is found. This behaviour is determined by the minimisation of the bond distortion with respect to the pure compounds, as the authors demonstrate with the use of a thermodynamic model. The same model also allows them to discuss the deviation from the randomness and phase diagrams. The mixing enthalpy hm is determined from the distortion energies of the five tetrahedra which form the basic lattice framework of these solutions. The configurational entropy sm is described by a III-order quasi-chemical approximation using the same tetrahedra as basic clusters. The minimisation of the free energy gm=hm-Tsm determines the equilibrium configuration. The computed distributions of bond lengths in several II-VI and III-V pseudo-binary alloys are in perfect agreement with the experiment and the thermodynamic properties also agree quite well with the existing experimental data. A sharp distinction is made between the behaviour of lattice-matched and lattice-mismatched alloys. The former have a binary-like phase diagram and tend to segregate below the critical temperature. The latter have more structured phase diagrams. In this case the stabilising effect of the elastic strain is outlined and the tendency to form ordered phases is identified
Local structure and thermodynamics of II-VI and III-V semiconductors by EXAFS
No full textL'ordre à courte distance des solutions solides II-VI a été étudié par EXAFS. Les énergies de distorsion des cinq tétraèdres formant le réseau de ces solutions ont été évaluées par un simple modèle VFF (Valence Force Field). Nous avons calculé, dans ce modèle, les énergies libres de mélange, les distributions de probabilité et les diagrammes de phases pour différents alliages II-VI et III-V, à partir de l'approximation quasi chimique du III ordre.The short-range order of II-VI substitutional solid solutions is investigated experimentally using the EXAFS technique. The distortion energies of the five tetrahedra which form the basic lattice framework of these solutions are evaluated by a simple Valence-Force-Field (VFF) model. Within the modified (III order) Quasi Chemical Approximation, we compute the free energy of mixing, the probability distribution and the coherent phase diagrams of several II-VI and III-V pseudobinary alloys
ANGLE-RESOLVED EXTENDED ENERGY-LOSS FINE-STRUCTURE ON CO2 - ANALOGIES AND DIFFERENCES WITH PHOTOABSORPTION RID G-7348-2011
No full textAN ANGULAR RESOLVED ELECTRON-ENERGY-LOSS INVESTIGATION OF HIGHLY ORIENTED PYROLITIC GRAPHITE ELECTRONIC-STRUCTURE RID G-7348-2011
No full textAngular resolved electron energy loss measurements on highly oriented pyrolitic graphite have been performed in reflection kinematics and at grazing incidence angles. Because of the selected kinematics it has been possible to change, almost independently, either the momentum transfer parallel to the surface (q(parallel-to)) or the angle between the momentum transfer and the graphite c axis (q^c). The present measurements have proved to be very sensitive to the surface structure of the sample and have allowed the assignment of the prominent loss at about 6 eV to a pi --> pi* excitation mainly localized perpendicular to the c axis. Possible contributions from surface localized states have also been detected. This transition shows negligible dispersion in q(parallel-to) and its energy centroid appears to be shifted with respect to previous surface and bulk measurements. Furthermore, the measured cross-sections are brought to the same relative scale for each grazing angle, and the loss and scattering functions are derived from data taken in reflection kinematics. The relevance of the kinematic prefactor in deriving transition energies from loss spectra is discussed with an emphasis on the role of q(parallel-to) zeroes
Corrosion Behaviour of Al, Cu, and Fe Alloys in Deep Sea Environment
Get PDFCorrosion Behaviour of Al, Cu, and Fe Alloys inDeep Sea EnvironmentG. Luciano, P. Letardi, P. Traverso, L. BelsantiThe aimof this study is to investigate deep sea environment effects on the corrosion of Al, Fe, and Cu alloys, employedin the KM3NeT project, a deep sea infrastructure designed to host a neutrino telescope. Alloys commonly used inseawater, as well as less widely employed materials were studied. Samples were immersed at the NEMO site (locatedoff Capo Passero, Italy; 3365 mdepth) for consecutive time periods of 6, 12 and 18 months. A representative set ofsamples was recovered and laboratory tests performed to evaluate the type and degree of corrosion attack. Stainlesssteels reported the best performance in terms of weight loss, corrosion rate, and corrosion morphology. However, alsoAl 5093 and Al 6082 performed satisfactorily, in terms of weight loss and corrosion rate. This prescreening will bepartially employed in selecting buildingmaterials for the KM3NeT structure
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
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