[en] In this work, Al_xGa_1_−_xN (x = 0; 0.1; 0.3; 0.5; 0.65; 0.7; 0.8; 1) wurtzite epilayers, grown on c-plane sapphire substrates, have been irradiated with Swift Heavy Ions at GANIL facility. Modifications induced by irradiation are characterized with in-situ optical absorption spectroscopy at 15 K. Spectra of these irradiated alloys exhibit optical absorption band formation, related to new energy levels in their bandgaps, whose positions only depend on the composition of the layer. However, these absorption bands are not observed in the Al_xGa_1_−_xN with Al molar fraction less than 0.3, likely because the energy level of the corresponding defect is located above the conduction band. Moreover, using different irradiation conditions, a coupled effect between nuclear collisions and electronic excitations for these color center creation have been investigated. A synergy between these two phenomena has been shown and appears to be independent of the composition of the alloy.

[en] In Senegal 80% of the energy consumption is still in the form of wood. Therefore, a large reforestation programme is initiated for which water is necessary. Besides using water of wind pumps for tree plantations and vegetable growing projects, the windmills are used for domestic uses and drinking water for animals. Women are the best users of wind pumps. The main problem regarding the use of wind pumps is maintenance. During several years one organization was in charge of maintenance. But as distances (also between wind pumps) are very large and it formerly was a governmental organization, it did not have the power to survive. Also, many farmers did not have the money to pay this organization properly for the maintenance. The most important aspect however, is that donors only support the windpump: its installation and maintenance are excluded. In some cases it appeared that installation of wind pumps was only executed for political reasons, which resulted in no maintenance and therefore in a bad promotion of wind energy. 4 refs

[en] This paper details in-situ studies of modifications induced by swift heavy ion irradiation in α-Al2O3. This complex behaviour is intermediary between the behaviour of amorphizable and non-amorphizable materials, respectively. A unique combination of irradiation experiments was performed at the IRRSUD beam line of the GANIL facility, with three different characterisation techniques: in-situ UV–Vis absorption, in-situ grazing incidence X-Ray diffraction and ex-situ transmission electron microscopy. This allows a complete study of point defects, and by depth profile of structural and microstructural modifications created on the trajectory of the incident ion. The α-Al2O3 crystals have been irradiated by 92 MeV Xenon and 74 MeV Krypton ions, the irradiation conditions have been chosen rather similar with an energy range where the ratio between electronic and nuclear stopping power changes dramatically as function of depth penetration. The main contribution of electronic excitation, above the threshold for track formation, is present beneath the surface to finally get almost only elastic collisions at the end of the projected range. Amorphization kinetics by the overlapping of multiple ion tracks is observed. In the crystalline matrix, long range strains, unit-cell swelling, local microstrain, domain size decrease, disordering of oxygen sublattice as well as colour centre formation are found. This study highlights the relationship between ion energy losses into a material and its response. While amorphization requires electronic stopping values above a certain threshold, point defects are predominantly induced by elastic collisions, while some structural modifications of the crystalline matrix, such as unit-cell swelling, are due to contribution of both electronic and nuclear processes.

[en] Recent work has shown that electronic excitations play a role in the creation of optical point defects in AlN although the material had been considered during a long time as insensitive to electronic energy loss and radiolysis. We address here an indirect observation of the effect of electronic excitations on point defect in AlN. Unprecedented climb of screw dislocations under swift heavy irradiation in irradiated AlN is studied. This is a sign to point defect diffusion towards the dislocation, which allows the increase of the length of the dislocation line. It is demonstrated that the climb, thus the point defect creation and/or their mobility is mainly induced by electronic excitations. This happens above an electronic stopping power threshold much lower than the one for ion track formation in AlN. This climb of dislocation was also observed for the same irradiation conditions in Al_xGa_1−xN (x = 0.5; 0.7; 0.8).

[en] In this work, GaN epilayers, grown on (0 0 0 1) sapphire substrate, were studied under swift heavy ion irradiation with a broad variety of projectiles at different energies. Several characterization techniques including transmission electron microscopy, optical absorption spectroscopy and Raman scattering spectroscopy, employed for different irradiation conditions, allowed the identification and the attribution of the origin of the observed modifications. It has been established that for projectiles presenting an electronic stopping power higher than a threshold of 17 keV.nm⁻¹, there was the formation of disordered latent tracks on the ion paths. We have shown that these tracks become more continuous and are visible until a higher depth with the increase of the projectile electronic stopping power. We have also highlighted that the latent tracks induce the appearance of a biaxial stress of the order of some GPa and strongly modify the optical bandgap values. Contrary to this effect of electronic energy loss, the atomic displacements generated by nuclear energy loss process did not imply significant biaxial stress and optical bandgap closing.

[en] Like many countries in Africa, Senegal is facing economical decline, energy crisis and serious desertification problem in rural areas. These issues could be removed if renewable energy is used as a primary source of energy in rural areas. What is required is a strategy to implement renewable energy technologies at large scale. The government and many non-governmental organisations (NGOs) have tried to comprehend and have strived to address the problem of energy. This paper present a review of activities in the field of renewable energy applications in Senegal, which goes back to the mid 1970s and will discuss the socio-economic benefits that the country has derived from these environmentally sound and appropriate sources of energy. The development and trial of systems were mostly funded so far by donor agencies in collaboration with government and NGOs. Among the applications being supported are solar lighting, water pumping and small power plants. Recent efforts have been aimed at restructuring the programmes and giving them a market orientation. Future trends, some suggestion and recommendations for successful dissemination of renewable energy sources are also drawn. The present situation is seen to be much more promising and favourable for renewable energy. (Author)

[en] Nano-structuration has opened the way for designing materials with improved properties by taking advantage of multiple interfaces providing enhanced local physical properties. In this frame, nanostructured materials are envisioned for nuclear applications due to severe environmental conditions (radiation, temperature, corrosion ... ). Here we report a study based on IBA (RBS and NRA) of a nanometric Cr/Ta multilayer coating demonstrating an extremely high radiation tolerance. TEM was also performed to confirm RBS results. Multilayer coated samples were firstly implanted with helium ions, and NRA analyses revealed that an optimized geometry can accommodate up to 20 at. % of gas without noticeable damage, implanted atoms being probably stored at the Cr/Ta interfaces. Heavy ion irradiation was also performed at room temperature (RT) and 400 degrees C, mimicking nuclear reactor neutron bombardment. Although we detected the growth of mixing layers at the Cr/Ta interfaces upon irradiation, these newly created layers remain much thinner than those produced at a single interface, preserving the initial multilayer arrangement. (authors)

[en] Wurtzite GaN epilayers, grown on the c-plane of sapphire substrate, have been irradiated with swift heavy ions at different energies and fluences, and thereafter studied by Raman scattering spectroscopy, UV–visible spectroscopy and transmission electron microscopy. Raman spectra show strong structural modifications in the GaN layer. Indeed, in addition to the broadening of the allowed modes, a large continuum and three new modes at approximately 200 cm"−"1, 300 cm"−"1 and 670 cm"−"1 appear after irradiation attributed to disorder-activated Raman scattering. In this case, spectra are driven by the phonon density of states of the material due to the loss of translation symmetry of the lattice induced by defects. It was shown qualitatively that both electronic excitations and elastic collisions play an important role in the disorder induced by irradiation. UV–visible spectra reveal an absorption band at 2.8 eV which is linked to the new mode at 300 cm"−"1 observed in irradiated Raman spectra and comes from Ga-vacancies. These color centers are produced by elastic collisions (without any visible effect of electronic excitations).