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.

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

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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

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

Mechanical properties of Al/Al2O3 nanolaminated films: correlation to microstructure

peer reviewedaudience: researcher, professional, studentWear resistance and the hardness of Al/Al2O3 nanolaminated films were investigated in this study. Monolithic films and multilayers were deposited on a silicon substrate with two different substrate temperatures: T-s= 25 degrees C and T-s= -90 degrees C. The period thickness of multilayers was lowering from 40 to 2 nm. From nanoindentation measurements, it appears that the hardness of multilayers has an intermediate value between those of metal (Al) and ceramic (Al2O3). The tribological test was conducted by the pin-on-disc method. The T-s=25 degrees C deposited multilayers, as well as single films, demonstrated poor wear resistance. The best wear resistance was obtained for multilayers deposited at the lowest substrate temperature (T-s= -90 degrees C). The results are ill good agreement with structural characterization. X-ray reflectometry demonstrated that the multilayer character of Al/Al2O3 is more pronounced for T-s= -90 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved

Nanoindentation investigation of Ti/TiN multilayers films

peer reviewedThe hardness of Ti/TiN nanolaminated films is investigated in this study. Monolithic Ti and TiN films and Ti/TiN multilayers were deposited on silicon substrates by radio-frequency sputtering. The period thickness of multilayers was decreased from 20 to 2.5 nm. Grazing x-ray reflectometry showed that the modulation of composition of Ti/TiN multilayers exists for all the period thickness considered. From nanoindentation measurements, we determined the hardness and Young's modulus of multilayers. Hardness increased with decreasing period thickness to go beyond the rule-of-mixture value for samples with period thickness of Lambda less than or equal to 5 nm. The maximum hardness, 1.6 times higher than the value obtained by the rule of mixture, is obtained for Lambda=2.5 nm. Our results are compared to a dislocation-based model previously introduced by Lehoczky. (C) 2000 American Institute of Physics. [S0021-8979(00)09411-1]

Infrared properties of YBa 2 Cu 3 O 7 and Bi 2 Sr 2 Ca n − 1 Cu n O 2 n + 4 thin films

International audienceWe report room-temperature optical reflectivity and transmission measurements on a variety ofYBa2Cu307 and Bi2Sr2Can -1CUn02n +4 thin films in the 500-25000 cm-1 frequency range. Reflectivitydata when not biased by the substrate are used to compute the optical conductivity. A comparison ofour results with published reflectivity data on single-domain YBa2Cu307 crystals suggests an overwhelmingcontribution of the CU02 planes {with respect to the chains} to the optical conductivity. The datacan be analyzed in terms of a Drude low-frequency contribution and a so-called midinfrared band. However,the anomalous infrared response appears to be uniquely described by a generalized Drude response:for all the samples investigated, the relaxation rate (which increases linearly with frequency) and theeffective mass are found to be the same as a function of frequency