Optical Properties of Layered Superconductors near the Josephson Plasma Resonance

We study the optical properties of crystals with spatial dispersion and show that the usual Fresnel approach becomes invalid near frequencies where the group velocity of the wave packets inside the crystal vanishes. Near these special frequencies the reflectivity depends on the atomic structure of the crystal provided that disorder and dissipation are very low. This is demonstrated explicitly by a detailed study of layered superconductors with identical or two different alternating junctions in the frequency range near the Josephson plasma resonance. Accounting for both inductive and charge coupling of the intrinsic junctions, we show that multiple modes are excited inside the crystal by the incident light, determine their relative amplitude by the microscopic calculation of the additional boundary conditions and finally obtain the reflectivity. Spatial dispersion also provides a novel method to stop light pulses, which has possible applications for quantum information processing and the artificial creation of event horizons in a solid.Comment: 25 pages, 20 figures, submitted to Phys. Rev.

Genetic diversity and phylogenetic relationships among the annual Cicer species as revealed by isozyme polymorphism

There are few estimates of genetic variability within and among populations of the nine annual Cicer species and for the wild species this information is based on few accessions. The present study was undertaken to examine genetic variation within and between annual Cicer species. One hundred and thirty-nine accessions of nine annual Cicer species were used for electrophoretic analysis at ICARDA. High levels of polymorphism in all eight wild annual Cicer species was found. This is in contrast to earlier research which had shown high polymorphism only in C. reticulatum. Cicer reticulatum had the highest proportion of polymorphic loci. However, for the cultigen, among 14 loci assayed, only two were polymorphic, ADH and PGD2. The nine species formed four phylogenetic groups based on the neighbor-joining method. The first group comprised C. arietinum, C. Reticulatum and C. echinospermum, the second C. bijugum, C. judaicum and C. pinnatifidum, the third C. chorassanicum and C. yamashitae; and the fourth group consisted of one species, C. cuneatum. The phylogenetic tree developed from the neighbor-joining technique illustrated that C. reticulatum is the probable progenitor of C. arietinum and that C. echinospermum split off from a common ancestor at an earlier stage in the evolutionary history of Cicer. Genetic diversity data showed that the greatest diversity was within C. reticulatum and the lowest with the cultigen, C. arientinum. With the exception of C. reticulatum, genetic diversity increased with genetic distance from the cultigen. Little geographic variation in genetic diversity was found

Elaboration and characterization of Ti and TiN thin films and multilayers for hard coating applications

In this paper, we report on the growth of titanium and titanium nitride thin films and of Ti/TiN nanometric multilayers. The elaboration ofthese films has been carried out by high-vacuum diode r.f. sputtering. The growth was monitored in-situ by kinetic ellipsometry. The filmthickness ranged from 50 to 200 nm for the Ti and TiN single layers. For the multilayers, the thickness of each component was varied from1 nm to 10 nm and alternately repeated in order to obtain a total thickness of 200 nm. After deposition, the films were characterised by meansof X-ray diffraction, grazing incidence X-ray reflectometry, atomic force microscopy and transmission electron microscopy for structuraldetermination. A comparison is made between the microstructural and the mechanical properties of Ti and TiN films on the one hand and themultilayers on the other hand (porosity, density and so on). We show that the wear properties are increased by multilayering

Apport des techniques biochimiques et moléculaires pour la caractérisation des champignons pathogènes des légumineuses à grosses graines, dans les pays du pourtour méditerranéen.

International audienc

Etude des propriétés mécaniques des multicouches métal/céramique

International audienceMultilayers of alternative metal and ceramic (nitrid) present attractive tribological properties. The aim of this study is to correlate the hardness with the structural properties.Multilayers films of Ti-TiN with a period thickness equal 20,10,8,5 and 2.5 nm, were deposited by RF reactive sputtering on silicon substrates with a metallic target. The deposition was done at room temperature for T-TiN.The total and period thickness for all the films, were measured by Grazing X-Ray Reflectometry. The hardness was measured by nanoindention with a Berkovich diamond indentor. For T-TiN the hardness increases with decreasing period thickness to go beyond the rule-of-mixture value for samples with period thickness Lambda less than or equal to 5 nm. The maximum hardness, 1.6 times higher than the rule of mixture value, is obtained for Lambda = 2.5 nm. However a similar tribological behavior was obtain for these two systems. Wear resistance increases when the period thickness decrease and shows a maximun value for the smallest A, superior to those of monolithic layers TiN and Al2O3

Tribological Properties of Ti/Tin Nanomultilayers

AbstractThe tribological behaviour of Ti/TiN amorphous nanometric multilayers is reported in comparison with that of single Ti and TiN layers, in order to study the wear mechanism of nanostructures submitted to that one may call “macroscopic loading”. Ti/TiN nanolayers were deposited onto Si substrate by high vacuum diode r.f. sputtering assisted by in-situ kinetic ellipsometry. Transmission Electron Microscopy (T.E.M.) characterization exhibited the multilayered structure of the films, ascertained by grazing angle X-ray reflectometry and ellipsometry. Sliding wear tests against alumina in dry air showed the ceramic-typed behaviour of the multilayers, the wear of which was partly governed through a microfracture mechanism. Their wear lifetime was found to be higher than that of Ti and TiN single layers and increased with the number of layers.</jats:p