Irreversible transformation of ferromagnetic ordered stripe domains in single-shot IR pump - resonant X-ray scattering probe experiments

The evolution of a magnetic domain structure upon excitation by an intense, femtosecond Infra-Red (IR) laser pulse has been investigated using single-shot based time-resolved resonant X-ray scattering at the X-ray Free Electron laser LCLS. A well-ordered stripe domain pattern as present in a thin CoPd alloy film has been used as prototype magnetic domain structure for this study. The fluence of the IR laser pump pulse was sufficient to lead to an almost complete quenching of the magnetization within the ultrafast demagnetization process taking place within the first few hundreds of femtoseconds following the IR laser pump pulse excitation. On longer time scales this excitation gave rise to subsequent irreversible transformations of the magnetic domain structure. Under our specific experimental conditions, it took about 2 nanoseconds before the magnetization started to recover. After about 5 nanoseconds the previously ordered stripe domain structure had evolved into a disordered labyrinth domain structure. Surprisingly, we observe after about 7 nanoseconds the occurrence of a partially ordered stripe domain structure reoriented into a novel direction. It is this domain structure in which the sample's magnetization stabilizes as revealed by scattering patterns recorded long after the initial pump-probe cycle. Using micro-magnetic simulations we can explain this observation based on changes of the magnetic anisotropy going along with heat dissipation in the film.Comment: 16 pages, 6 figure

Etude des matériaux corrélés de terres rares par diffusion résonante inélastique des rayons X

PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

In situ TEM thermal annealing of high purity Fe10wt%Cr alloy thin foils implanted with Ti and O ions

International audienceODS steels are ferritic-martensitic steels reinforced with (Y,Ti) oxide dispersions to enhance the creep and radiation resistance at elevated temperatures. Their conventional fabrication is achieved by ball milling followed by high-temperature consolidation. An alternative approach of ion beam synthesis has been suggested recently to study the early precipitation stages of oxide nanoparticles. To clarify the details of Ti-based oxide nanoparticle precipitation, Ti+ and O+ ions were implanted into high-purity Fe-10 wt%Cr thin foils at room temperature and subjected to thermal annealing. Nano-size oxide particles and larger surface oxide islands with pronounced Cr enrichment were observed after in situ Transmission Electron Microscopy (TEM) annealing at 600 °C and were identified as a mixed iron-chromium spinel. The features observed after ex situ annealing at 800 °C were also identified as iron-chromium oxide, but with a certain titanium enrichment. The observations thus suggest that titanium plays no major role in the early stages of oxide precipitation

Nano-Structured Materials under Irradiation: Oxide Dispersion-Strengthened Steels

International audienceOxide dispersion-strengthened materials are reinforced by a (Y, Ti, O) nano-oxide dispersion and thus can be considered as nanostructured materials. In this alloy, most of the nanoprecipitates are (Y, Ti, O) nano-oxides exhibiting a Y$_{2}$Ti$_{2}$O$_{7}$ pyrochlore-like structure. However, the lattice structure of the smallest oxides is difficult to determine, but it is likely to be close to the atomic structure of the host matrix. Designed to serve in extreme environments—i.e., a nuclear power plant—the challenge for ODS steels is to preserve the nano-oxide dispersion under irradiation in order to maintain the excellent creep properties of the alloy in the reactor. Under irradiation, the nano-oxides exhibit different behaviour as a function of the temperature. At low temperature, the nano-oxides tend to dissolve owing to the frequent ballistic ejection of the solute atoms. At medium temperature, the thermal diffusion balances the ballistic dissolution, and the nano-oxides display an apparent stability. At high temperature, the nano-oxides start to coarsen, resulting in an increase in their size and a decrease in their number density. If the small nano-oxides coarsen through a radiation-enhanced Ostwald ripening mechanism, some large oxides disappear to the benefit of the small ones through a radiation-induced inverse Ostwald ripening. In conclusion, it is suggested that, under irradiation, the nano-oxide dispersion prevails over dislocations, grain boundaries and free surfaces to remove the point defects created by irradiation

Radiation-induced sharpening in Cr-Coated zirconium alloy

International audienceTo improve the safety of nuclear power plants, a Cr protective layer is deposited on zirconium alloys to enhance oxidation resistance of the nuclear fuel cladding during both in-service and hypothetical accidental transients at High Temperature (HT) in Light Water Reactors. The formation of the Cr2O3 film on the coating surface considerably helps in reducing the oxidation kinetics of the zirconium alloy, especially during hypothetic Loss of Coolant Accident (LOCA). However, if the Cr coating is successful to increase the oxidation resistance at HT of the zirconium substrate, for in-service conditions, under neutron irradiation, Cr desquamation has to be avoided to guarantee a safe use of the Cr-coated zirconium alloys. Therefore, the adhesion properties have to be maintained despite the structural defects created by sustained neutron irradiation in the reactor environment. This paper proposes to study the behavior of the Zircaloy-Cr interface of a first generation Cr-coated material during a specific in situ ion irradiation. As deposited, the Cr-coated sample presents a f.c.c. C15 Laves-type intermetallic phase at the interface with off-stoichiometric composition. After irradiation and for the specific conditions applied, this interfacial phase has significantly dissolved. Energy Dispersion Spectroscopy revealed that the dissolution was accompanied by a counterintuitive “sharpening” effect.</jats:p

Optical, structural and aging properties of Al/Sc-based multilayers for the extreme ultraviolet

International audienceThis manuscript presents the structural characterization of Al/Sc-based periodic multilayer coatings for the extreme ultraviolet (EUV) spectral range. Based on transmission electron microscopy and electron diffraction as well as grazing-incidence and large-angle x-ray diffraction, a model for the layer structure and the interfacial effects of Al/Sc coatings is built. The onset of crystallization in nanoscale Al and Sc layers as a function of thickness is also revealed in these characterizations. The Al/Sc layer model is validated and further refined by fitting in-band and out-of-band EUV reflectance measurements across 5 orders of magnitude in an extended wavelength range from 17 to 80 nm. The same type of EUV reflectance measurements is used to test the Al/Sc aging properties and to demonstrate the spectral response of optimized two- and tri-material multilayers including Al/Sc, Al/Sc/SiC and Mo/Al/Sc

Towards the synthesis of mixed oxides with controlled stoichiometry from Prussian blue analogues

International audienceControlling the synthesis of mixed oxides is of great interest since their stoichiometry influences the properties. We present here the transformation of the Co4[Fe(CN)6]2.7 Prussian blue analogue (PBA) into the mixed Co1.8Fe1.2O4 spinel oxide, with a detailed characterization of the final phase (obtained by calcination in air at 900 °C for 2 hours) and an emphasis on the calcination process by TDA/TGA, X-ray diffraction, (high-resolution) TEM and energy-filtered TEM. Single-crystalline particles with a homogeneous distribution of Fe and Co ions within each particle are observed, with the same Co : Fe ratio as in the PBA. The calcination mechanism is a 2-step transformation, with first the elimination of water molecules and then the cyanide decomposition. XRD and TEM at intermediate temperatures additionally show the occurrence of a phase separation between 500 °C and 850 °C before the formation of the single final phase. We demonstrate also through the calcination of intermediate PBAs between Co4[Fe(CN)6]2.7 and Co4[Co(CN)6]2.7 that this synthesis route leads to the perfect control of the oxide stoichiometry through control of the PBA. The versatility of this synthesis route is finally illustrated through the successful synthesis of Co1.8Fe1.2O4 nanoparticles (diameter ∼5 nm) from PBA nanoparticles confined within the pores of a mesoporous silica monolith

Electrochemical study and experimental simulation of the synergistic effect of a formulation based on Ficus pumila Linn. Leaves extract and zinc sulfate on the XC38 steel corrosion inhibition in NaCl solution

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Comparison between Lacunary and Saturated Keggin POMS as Steel Corrosion Inhibitors in Chloride Solution: Contribution of the Lacuna in the Inhibition Mechanism Process and Elucidation of the Protection Mechanism

International audiencePW 11 O 39 ].14H 2 O and K 9 [AlW 11 O 39 ].15H 2 O) on the corrosion inhibition of XC38 steel in NaCl 0.1 M was investigated. Electrochemical methods (polarization curves and electrochemical impedance spectroscopy) showed that the presence of controlled amounts of these compounds improved protection of the steel against corrosion. These results were supported by surface analysis, where only a minor amount of rust was produced on metal surface in the presence of polyoxometalates (POMs). The lacunary POMs were more efficient compared to their saturated species, highlighting the key role played by the lacuna on the inhibition process. Efficiency of POMs (both saturated and lacunary) was explained by their ability to increase the Fe(II)/Fe(III) molar ratio in greenish protective oxide layer formed upon steel oxidation. The mechanism proposed clearly explains the higher efficiency observed with lacunary POMs, in relation to their ability to react with free Fe(III) to yield a substituted structure

BIODETECT 2014 campaign in Paris area : Overview of the experimental strategy and preliminary results

During summer 2014 (June to August) the BIODETECT 2014 campaign took place at two sites in the region of Paris, France: CEA/Saclay (suburban) and Paris/ LHVP (urban). A set of innovative fluorescence instruments have been deployed to compare their ability to detect and characterize in real time the bioaerosol present in urban and suburban atmospheres. All on line fluorescence instruments were calibrated with the same, fresh sets fluorescent polystyrene latex (PSL) spheres at the start, middle, and end of the campaign for quality control. To understand atmospheric and biological processes involved in the fluorescent particulate matter observed, microscopic identification and collection onto species-specific agar gelwas performed every 30 minutes during several periods of the campaign. Analysis of chemicals tracers (e.g. arabitol, mannitol) was performed by a novel real-time technique to track specific fungal spores events by coupling a Particle Into Liquid Samples (PILS) to a triple quad mass spectrometer (ABSCIEX). The sampling sites were often impacted by anthropogenic sources and pollution events from Paris. To constrain the data set a full range of instruments commonly used in atmospheric science were used. PM1 mass in each of several common chemical fractions (e.g. sulfate, nitrate, organics, chloride) was provided via ACSM. Also recorded was: size distribution of particle number between 10 nm to 20 µm (TSI, SMPS and APS), total aerosol mass (TEOM-FDMS), combustion tracers (Aethalolmeter AE33), and traces gases measurements like VOC (PTRMS) NOx and Ozone (Teledyne). Ice nuclei (IN) studies have been performed to identify size-resolved concentrations of IN. We present here our preliminary results on the inter-comparison methods to detect bioaerosols in the atmosphere