Direct Observation of Propagating Gigahertz Coherent Guided Acoustic Phonons in Free Standing Single Copper Nanowires

We report on gigahertz acoustic phonon waveguiding in free-standing single copper nanowires studied by femtosecond transient reflectivity measurements. The results are discussed on the basis of the semianalytical resolution of the Pochhammer and Chree equation. The spreading of the generated Gaussian wave packet of two different modes is derived analytically and compared with the observed oscillations of the sample reflectivity. These experiments provide a unique way to independently obtain geometrical and material characterization. This direct observation of coherent guided acoustic phonons in a single nano-object is also the first step toward nanolateral size acoustic transducer and comprehensive studies of the thermal properties of nanowires

Structure and microstructure evolution of Al-Mg-Si alloy processed by equal-channel angular pressing

An ultrafine grained Al–Mg–Si alloy was prepared by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Samples were ECAPed through a die with an inner angle of F = 90° and outer arc of curvature of ¿ = 37° from 1 to 12 ECAP passes at room temperature following route Bc. To analyze the evolution of the microstructure at increasing ECAP passes, X-ray diffraction and electron backscatter diffraction analyses were carried out. The results revealed two distinct processing regimes, namely (i) from 1 to 5 passes, the microstructure evolved from elongated grains and sub-grains to a rather equiaxed array of ultrafine grains and (ii) from 5 to 12 passes where no change in the morphology and average grain size was noticed. In the overall behavior, the boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 5 passes and at a lower rate from 5 to 12 passes. The crystallite size decreased down to about 45 nm with the increase in deformation. The influence of deformation on precipitate evolution in the Al–Mg–Si alloy was also studied by differential scanning calorimetry. A significant decrease in the peak temperature associated to the 50% of recrystallization was observed at increasing ECAP passes.Peer ReviewedPreprin

Severe plastic deformation for producing superfunctional ultrafine-grained and heterostructured materials: An interdisciplinary review

Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life

Analyse de mesures radiométriques de simulation SPOT en milieux méditerranéens aride et sub-humide

International audienceDes mesures radiométriques au sol et aéroportées ont été réalisées le long de transects en milieux méditerranéens arides (Haut Atlas oriental, Maroc) et sub-humide (Garrigues du Montpelliérais, France). Les résultats présentés concernent les valeurs de réflectances mesurées dans les 3 bandes spectrales de SPOT : mesures ponctuelles mesurées au sol pour les espèces végétales dominantes et valeurs moyennes observées par télédétection aéroportée pour les unités de végétation. L'analyse le long de transects permet également de mettre en évidence les structures spatiales des couverts végétaux étudiés

THE GROWTH OF V2O5 FLASH-EVAPORATED FILMS

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LITHIUM INTERCALATION IN MOO3 - A COMPARISON BETWEEN CRYSTALLINE AND DISORDERED PHASES

We report properties of lithium-intercalated MoO3 crystalline and thin-film which are potential cathode materials for high energy density batteries. Discharge and charge reactions of MoO3 electrodes in a non-aqueous Li+-electrolyte have been studied. The kinetically accessible discharge range amounts to 0 less-than-or-equal-to x less-than-or-equal-to 1.5 for Li insertion in LixMoO3. Transport parameters such as the Li+ chemical diffusion coefficient, thermodynamic factor and ionic conductivity are investigated during the Li+ insertion process and discussed with respect to the crystallinity of the cathode material.59217317

THE GROWTH AND ELECTROCHEMICAL PROPERTIES OF V6O13 FLASH-EVAPORATED FILMS

The growth of V6O13 films is reported for the first time. We have investigated the structural, optical, and electrical properties of flash-evaporated polycrystalline films and how these properties are affected by different thin-film preparation conditions. The highest quality films were grown on silicon substrate maintained at 250 degrees C. Microbatteries fabricated with cathode formed at moderate temperature exhibit a monotonous discharge voltage curve, indicating that the material remains in a single phase even for high degree of lithium intercalation. For cathode films prepared at 250 degrees C, lithium diffusivity is 10(-13) cm(2) s(-1) in LixV6O13.764167113314

Validation of actual evapotranspiration simulations with satellite thermal IR data

International audienc

A comparison of LANDSAT-MSS, HCMM and NOAA-AVHRR features for identifying dominant vegetation patterns in mediterranean areas.

International audienc