Ultra-low reflection porous silicon nanowires for solar cell applications

International audienceHigh density vertically aligned Porous Silicon NanoWires (PSiNWs) were fabricated on silicon substrate using metal assisted chemical etching process. A linear dependency of nanowire length to the etching time was obtained and the change in the growth rate of PSiNWs by increasing etching durations was shown. A typical 2D bright-field TEM image used for volume reconstruction of the sample shows the pores size varying from 10 to 50 nm. Furthermore, reflectivity measurements show that the 35% reflectivity of the starting silicon wafer drops to 0.1%, recorded for more than 10 µm long PSiNWs. Models based on cone shape of nanowires located in a circular and rectangular bases were used to calculate the reflectance employing the Transfert Matrix Formalism (TMF) of the PSiNWs layer. Using TMF, the Bruggeman model was used to calculate the refractive index of PSiNWs layer. The calculated reflectance using circular cone shape fits better the measured reflectance for PSiNWs. The remarkable decrease in optical reflectivity indicates that PSiNWs is a good antireflective layer and have a great potential to be utilized in radial or coaxial p-n heterojunction solar cells that could provide orthogonal photon absorption and enhanced carrier collection

Unified model for Mullins effect and high cycle fatigue life prediction of rubber materials

Proceedings of the 8th European Conference on constitutive models for rubbers (ECCMR VIII), San Sebastian, Spain, 25-28 June 2013International audienceThe study describes the basic principles of a general damage model (GDMF) for Mullins effect and high cycle fatigue loadings of rubber materials and demonstrates its prediction possibilities for simulating the complete fatigue failure phenomenon. The present paper focuses on stiffness modelling of rubber materials for uniaxial and multiaxial static and fatigue loadings with a minimal number of material parameters in order to ensure robustness of the identification. The proposed hyperplastic model is expressed in terms of classical independent strain invariants. Mullins effect and high cycle fatigue loadings are both modelled according to a continuum damage mechanics approach

SECM study of a chromium-free anticorrosion adhesion primer for aluminum 2024

International audienceHexavalent chromium, largely used for anticorrosion surface treatments of aluminum in aeronautics, will soon be completely banned due to its high toxicity (REACH regulation). Looking for an innovative solution, regarding both anticorrosion and adhesion properties, a chromium free replacement treatment directly inspired by the diazonium chemistry has been developed by the CEA (LICSEN). The evolution of the surface electrochemical properties was followed before and after grafting by means of scanning electrochemical microscopy (SECM). These studies showed that the native aluminum oxide layer is etched during the organic grafting step, which is performed in sulfuric acid. SECM also evidenced that the polymeric grafted film is porous enough to allow the reconstruction of this native aluminum oxide layer after the treatment. On the strength of these results, we decided to extend the thickness of the aluminum oxide layer by an anodization treatment, in the idea that Al$_2$O$_3$ could be formed through the organic layer without altering it. In that purpose, SECM was used to characterize the films and allow the determination of the best parameters for the organic coating (concentration, immersion time, diazonium function, rinsing, cleaning, additives…) and for the anodization process (duration, applied tension…). Thus, bi-functional coatings were obtained, giving very satisfying results both in terms of corrosion protection and adhesion with painting. This simple and low cost process has been patented . It validates standardized tests and could be swiftly industrializable

Radio Detection of Cosmic Ray Air Showers with Codalema

Studies of the radio detection of Extensive Air Showers is the goal of the demonstrative experiment CODALEMA. Previous analysis have demonstrated that detection around $5.10^{16}$ eV was achieved with this set-up. New results allow for the first time to study the topology of the electric field associated to EAS events on a event by event basis.Comment: 6 pages, 4 figures Proceedings of the Rencontres de Moriond, Very High Energy Phenomena in the Universe, La Thuile, Italy (March 12-19, 2005

Radio Detection of Extensive Air Showers with CODALEMA

The principle and performances of the CODALEMA experimental device, set up to study the possibility of high energy cosmic rays radio detection, are presented. Radio transient signals associated to cosmic rays have been identified, for which arrival directions and shower's electric field topologies have been extracted from the antenna signals. The measured rate, about 1 event per day, corresponds to an energy threshold around 5.10^16 eV. These results allow to determine the perspectives offered by the present experimental design for radiodetection of UHECR at a larger scale.Comment: 4 pages and 3 figures. To appear in the Proceedings of the 29th ICRC, Pune (2005

Symmetry of Magnetically Ordered Quasicrystals

The notion of magnetic symmetry is reexamined in light of the recent observation of long range magnetic order in icosahedral quasicrystals [Charrier et al., Phys. Rev. Lett. 78, 4637 (1997)]. The relation between the symmetry of a magnetically-ordered (periodic or quasiperiodic) crystal, given in terms of a ``spin space group,'' and its neutron diffraction diagram is established. In doing so, an outline of a symmetry classification scheme for magnetically ordered quasiperiodic crystals is provided. Predictions are given for the expected diffraction patterns of magnetically ordered icosahedral crystals, provided their symmetry is well described by icosahedral spin space groups.Comment: 5 pages. Accepted for publication in Phys. Rev. Letter

Radio Detection of Cosmic Ray Extensive Air Showers: present status of the CODALEMA experiment

Data acquisition and analysis for the CODALEMA experiment, in operation for more than one year, has provided improved knowledge of the characteristics of this new device. At the same time, an important effort has been made to develop processing techniques for extracting transient signals from data containing interference.Comment: september 200

Plasticity, elasticity, and adhesion energy of plant cell walls: nanometrology of lignin loss using atomic force microscopy

International audienceThe complex organic polymer, lignin, abundant in plants, prevents the efficient extraction of sugars from the cell walls that is required for large scale biofuel production. Because lignin removal is crucial in overcoming this challenge, the question of how the nanoscale properties of the plant cell ultrastructure correlate with delignification processes is important. Here, we report how distinct molecular domains can be identified and how physical quantities of adhesion energy, elasticity, and plasticity undergo changes, and whether such quantitative observations can be used to characterize delignification. By chemically processing biomass, and employing nanometrology, the various stages of lignin removal are shown to be distinguished through the observed morphochemical and nanomechanical variations. Such spatially resolved correlations between chemistry and nanomechanics during deconstruction not only provide a better understanding of the cell wall architecture but also is vital for devising optimum chemical treatments

Radiodetection of Cosmic Ray Extensive Air Showers

We present the characteristics and performance of a demonstration experiment devoted to the observation of ultra high- energy cosmic ray extensive air showers using a radiodetection technique. In a first step, one antenna narrowed band filtered acting as trigger, with a 4 $\sigma$ threshold above sky background-level, was used to tag any radio transient in coincidence on the antenna array. Recently, the addition of 4 particle detectors has allowed us to observe cosmic ray events in coincidence with antennas