Recent trends and climatic perspectives of hailstorms frequency and intensity in Tuscany and Central Italy

International audienceThe damages from climatic extremes have dramatically increased in the last decades in Europe, as likely outcomes of climate change: floods, droughts, heat waves and hailstorms have brought local as well as widespread damages to farmers, industry, infrastructures and society, to insurance and reinsurance companies; in this work we deal with the hailstorm hazard. The NCEP-NCAR Reanalysis (2.5 by 2.5° lat-lon) over the Italian area and the hailstorm reports at several sites are used to identify few forcings for hailstorms; statistical relationships linking forcings and hailstorm frequencies are derived. Such relationships are applied to the same forcings derived from the CGCM2-A2 climate scenario provided by the Canadian Centre for Climate modeling and analysis (CCCma; resolution approximately 3.75 by 3.75° lat-lon), to evaluate the expected changes of the frequency of hailstorms. The time series of the forcings from the NCEP-NCAR Reanalysis and the CCCma climate scenario in the past decades are compared in order to assess the reliability and accuracy of the predictions of the future hailstorm hazard. It is shown that the climate scenario provides a fairly faithful representation of the past trends of the forcings relevant to the hailstorms frequency and that such quantity, hence the hailstorm hazard, is growing and will likely grow in the future over the limited area taken into consideration in this study

Raman imaging characterization of structural and electrical properties in 4H SiC

International audienceRaman imaging measurements have been used to determine the spatial distribution of the doping level in n-type 4H-SiC wafers. The carrier concentration and mobility were determined from the line shape analysis of the LO phonon-plasmon coupled mode, using know procedures. The application of the method for mapping of the doping level at the wafer scale as well as in the vicinity of defects, for example micropipes, is demonstrated

Confocal Raman imaging for the study of HPHT and CVD diamond crystals and films

International audienceRecent improvements in the implementation of the technique make Raman spectroscopic imaging possible. Different systems have been developed to reduce recording and display times to reasonable levels.In this study, we have performed Raman imaging measurements for different HPHT or CVD diamond samples, and some test experiments will be presented. Results were qualitatively interpreted in terms of residual strain fields or variations in defect concentration in the different growth sectors. They illustrate the potential of Raman mapping or imaging for revealing the detail structure of diamond crystals or films

Raman imaging analysis of SiC wafers

International audienceRecent improvements in the implementation of the technique make Raman spectroscopic imaging possible. Different systems have been developed to reduce recording and display times to reasonable levels. In this study, we have performed Raman imaging measurements for different 4HSiC wafers, and some test experiments performed on defective samples will be presented. Results were qualitatively interpreted in terms of residual strain fields and variations in the carrier concentration in the vicinity of the defects

Deep Ultraviolet Raman Imaging with Micron Resolution: Application to Chemical-Vapor-Deposited Diamond Films

International audienceDeep ultraviolet (DUV) confocal Raman spectroscopy with excitation at 244 and 229nm was used to examine a specific chemical-vapor-deposited diamond film. By scanning the surface of this film, it was possible to construct DUV Raman images with micron resolution. The results were compared with those obtained using more conventional excitations in the visible (514 nm) or near-UV (363 nm) spectral ranges, and analyzed in terms of sensitivity and selectivity. DUV Raman images with micron resolution are, to the best of our knowledge, presented for the first time

Deep ultra-violet Raman imaging of CVD boron-doped and non-doped diamond films

International audienceDeep UV (244 nm) Raman images were recorded on CVD diamond films. The different images recorded on boron-doped polycrystalline film reveal large differences on the boron level within individual crystallites. Nevertheless, inspite of an enhanced intensity of the diamond line, the UV Raman spectra are less informative than the visible Raman spectra due to the weak response of the boron-related peaks. The images recorded on an un-doped homoepitaxial diamond film reveal a defective domain exhibiting in the same areas the sp3 CHx stretching vibration component and the first and second-order optical phonons of the graphite-like phonon bands of sp2 carbons embedded in a compressive zone of polycrystalline diamond

The effect of carbon nanolayers on wetting of alumina by NiSi alloys

International audienceIonocovalent oxides such as alumina, silica or magnesia are not wetted by Si and Si-rich alloys, the contact angles being close to 90A degrees. The aim of this work is to study the effect of submicron carbon layers on wetting in this type of system. In principle, silicon reacts with carbon to form silicon carbide, a compound wettable by Si alloys. However, the formation of silicon carbide at the interface can be affected by the dissolution of this compound into the molten alloy occurring in order to saturate the melt in carbon. These phenomena are studied using a model system consisting of Ni-63 at.%Si alloy and monocrystalline alumina substrate coated with carbon layers. Wetting experiments are performed by the dispensed drop technique in high vacuum varying the parameters: thickness of coating (from 0 to 100 nm), temperature and degree of carbon saturation of the alloy. The surfaces and reactive interfaces are characterised by SEM, X-ray microanalysis and XPS

UV and Visible Raman Spectroscopy Applied to s-Si/Si_1-xGe_x and s-SOI Multi-layer Systems

International audienceMechanical strain can be used to improve electronic transport properties in advanced short gate length Si-based Metal Oxide Semiconductor Field Effect Transistors. The controlled introduction of strain in the channel area of transistors (thanks to recessed SiGe sources and drains, contact etch stop layers or to previous processing at the wafer scale) can indeed increase the carrier mobility by a factor of up to two. We have used here ultra-violet and visible Raman Spectroscopy to study the processes that can influence strain during the elaboration of strained Si On Insulator (sSOI) substrates. The results obtained during analyses of tensily-strained Si layers grown on polished Si1-xGex virtual substrates (VS) show that the strain can be preserved for 20% of Ge. However, we observed a relaxation of the strain for 40% Ge, after layer transfer onto oxidized silicon. A definite strain relaxation at the edges of lines patterned in sSOI wafers was also demonstrated. A good agreement between experimental results and simulation has been achieved

Practical aspects of carbon content determination in carburized steels by EPMA

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