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Atomic Layer Etching of SiO2 using CF4 plasma in deposition mode at cryogenic temperature
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Electrical resistance of a glass-polymer bilayer under medium voltage for photovoltaic modules and related phenomena
No full textInternational audienceThe increase in voltage within photovoltaic networks enables significant reductions in CAPEX (Capital Expenditures) due to the use of smaller cable cross-sections. However, this voltage increase leads to an intensification of PID (Potential Induced Degradation) effects, which are already present at voltages below 1.5 kV. This work focuses on the electrical conduction and field distribution within PV modules through an electrical study of glass-polymer assemblies. Current measurements were carried out in a plane-to-plane configuration (with a guard electrode) on 10 cm² assemblies of a 3 mm thick glass sheet with a 500 µm laminated polymer film (encapsulant). Several assemblies of glasses and polymers were compared at different temperature and relative humidities. Monolayers of glass and polymers were also characterized. Glass-encapsulant assemblies were submitted to HVDC voltages at both polarities. The measured current is different in the two cases. Considering a soda-lime glass and a type of polyolefin, the current is at least four times larger when the glass is connected to the positive polarity than when it is connected to the negative one. Therefore, the two dielectrics do not behave like two resistors in series. In the glass, sodium ions (Na⁺) are known to migrate under the effect of the electric field. They can also enter the polymer and migrate through. If they are numerous enough, these charge migrations may change the field distribution in the dielectric. Tentative explanations of the observed differences in the steady-state current magnitudes are proposed considering these changes in the electric field distribution
Les bois d’architecture des sites birnirk et thulé (XIII-XVIIe s. de n. è.) : Développement du réseau de chronologies de largeurs de cernes dans l’ouest de l’Alaska
No full textInternational audienceAu tourant du IIe millénaire de notre ère, le détroit de Béring et le nord-ouest de l’Alaska sont le lieu d’importantes transformations culturelles, marquées par la transition des cultures Birnirk (VIII-XIIIe s.) et Punuk (IX-XIIIe s.) vers la culture Thulé (XIII-XVIIIe s.), ancestrale à la culture Inuit. Les recherches pour comprendre ces transformations sont en plein renouvellement, notamment par la dendroarchéologie. Le long des littoraux ouest-alaskiens, les bois d’architecture de sites birnirk et thulé sont très bien préservés dans les sols gelés. Dans ces régions de toundra sans arbres, les matériaux de construction sont des bois flottés, transportés par les grands fleuves et les courants marins, depuis les forêts de l’Intérieur et du Nord-ouest de l’Alaska jusqu’au littoraux. Le potentiel chronométrique et climatique de ces vestiges a été perçu dès les années 1930 par l’archéologue James Louis Giddings, pionnier de la dendrochronologie en Alaska. Ce dernier a construit une chronologie millénaire de largeurs de cernes (Picea glauca) dans le nord-ouest de l’Alaska (978-1948 de n. è.). Toutefois, l’origine multiple des bois dans les sites côtiers et l’essor de la datation radiocarbone dans les années 1950 ont conduit à l’abandon des études dendroarchéologiques en Alaska. Aujourd’hui, seule une chronologie, représentative du nord-ouest, est disponible pour réaliser la datation croisée des bois birnirk et thulé. Or, il a été montré, par l’étude du bois flotté moderne, qu’une majorité des bois échoués sur la côte ouest de l’Alaska provient de régions plus au sud, incluant le bassin du fleuve Yukon.Nous présentons ici le développement du réseau de chronologies de largeurs de cernes le long des littoraux ouest-alaskiens au cours des XIII-XVIIe s., combinant dendrochronologie conventionnelle et datation 14C wiggle-matching. Notre étude porte sur 274 sections d’épinette blanche (Picea glauca) issues des sites de Nukleet (XIII-XVIᵉ s.), de Pingusugruk (XIV-XVIIᵉ s.) et du Cap Espenberg (XIII-XVIIᵉ s.). La collection récente du Cap Espenberg (2010) fournit un bon cadre chronologique pour interpréter les schémas de croissance des bois de collections muséales plus anciennes.La dendrochronologie conventionnelle a permis de construire une dizaine de séquences flottantes, dont une commune à Pingusugruk et au Cap Espenberg dans le nord et le nord-ouest. Grâce à la datation 14C wiggle-matching, six d’entre elles, totalisant 20 bois, ont pu être placées dans un temps calendaire à résolution décennale, dépassant les imprécisions dues à la période plateau de la courbe de calibration radiocarbone (intervalles de temps de 150 à 300 ans). Les bois de Nukleet, plus au sud, se corrèlent à ces chronologies préliminaires, ce qui suggère une origine géographique partagée. Leur signal dendrochronologique est distinct de celui du nord-ouest, et ils sont très certainement issus des forêts intérieures de l’Alaska. Ces bois, associés à la séquence commune de Pingusugruk et du Cap Espenberg, forment désormais une chronologie qui s’étend du milieu du XIIIᵉ au début du XVIIᵉ siècle. Ces résultats offrent de nouvelles perspectives sur les itinéraires des bois flottés dans l’ouest de l’Alaska aux XIII-XVIIᵉ siècles. L'approche combinée dendrochronologie/14C wiggle-matching ouvre la voie au développement de chronologies de référence pour les régions intérieures, utiles à la datation croisée d’autres bois et à l’interprétation de leur signal climatique. À terme, ces chronologies renouvelées permettront d’affiner notre compréhension de l’environnement changeant dans lequel s’inscrivent les transformations culturelles à l’origine de la culture Inuit
Unravelling the Stability Stressors of Atomically Dispersed Fe–N–C Oxygen Reduction Catalysts
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Development of a Scintillation-Based Fast Neutron Multiplicity Counter for Nuclear Safeguards
No full textInternational audienceNondestructive assay measurements in the context of nuclear safeguards aim to estimate the parameters that characterize neutron multiplication in an interrogated system. Typical devices utilized in these assays consist of arrays of He-3 proportional counters inserted in a polyethylene lattice for neutron moderation. This process significantly increases the neutron mean lifetime against detection due to scattering in the detector, and thereby, it obstructs the measurement of the multiplying system time characteristics. Recently, it has been demonstrated that this issue may be overcome through the development of scatter-based detector arrays, which are sensitive to fast neutrons and do not require thermalization. This paper outlines the development of a new scatter-based neutron multiplicity counter composed of stilbene crystals and presents early results of the study. Data post-processing algorithms were developed in order to generate the neutron detection timeline using pulse shape discrimination. Physical parameters related to multiplication are inferred from the timeline analysis using the Feynman-alpha method. We produced a first Feynman-Y curve from a simple measurement of a Cf-252 source, alongside an MCNP model of the setup that accounted for the said measurement, showing a 33 % mean deviation between the two curves. Approximations in the modeling of the detection efficiency, which translates into a deviation of the simulated convergence value (), properly explain this discrepancy. In addition, the simulation consistently replicated the experimental neutron prompt decay constant (◻). We could therefore validate the simulation model and its associated algorithms, which will be used to dimension the final multiplicity-counting device. The detector performance parameters, such as the false neutron-counting rate, will also be studied in a near future
Experimental evaluation of the hydricity of hydrosilanes
No full textInternational audienceDespite their widespread use as reductants, the thermodynamic hydricities of hydrosilanes have not been determined experimentally. We report the hydricities of three triarylsilanes determined by a combination of hydride-exchange reactions and electrochemical measurements of the corresponding silylium cations. The hydricities in acetonitrile for Xyl3SiH (89.0 kcal·mol–1, Xyl = 2,6-dimethylphenyl), Mes3SiH (86.6 kcal·mol–1, Mes = 2,4,6-trimethylphenyl), and PEMP3SiH (80.5 kcal·mol–1, PEMP = pentamethylphenyl) were estimated from the one-electron reduction potentials of the silylium ions in 1,2-difluorobenzene and are higher than previously reported values obtained by calculations. The reaction of [PEMP3Si][B(C6F5)4] with cycloheptatriene (CHT) in 1,2-difluorobenzene/C6D6 (4:1) attained an equilibrium (K ≈ 1.3), indicating similar hydricities for CHT and PEMP3SiH
European NUCOBAM Project – Nuclear Components Based on Additive Manufacturing – Dispersion of Characterization in process qualification
No full textInternational audienceNUCOBAM aims at developing the qualification process and provide the evaluation of the in-service behaviour of additively manufactured austenitic stainless steel components in current nuclear installations, as a promising technique to tackle obsolescence challenges in operating reactors and manufacture new components with optimized design, for increased safety and efficiency. Among the different AM technologies that are currently available, NUCOBAM will focus on Laser Powder Bed Fusion (L-PBF) technology. The European consortium, composed of 13 partners, is combining its skills and resources to meet two major challenges of nuclear power plant components: the thermal ageing and corrosion of components, and the neutron irradiation effects in the core of the reactors for long in-service periods.The variability of the process is one another challenge specific to the process. For L-PBF process qualification, four partners have manufactured specimens and components as good as possible with their internal know-how without communicating on the parameters of the optimum process. An extensive mechanical test program was built on more than 700 L-PBF specimens: tensile tests, hardness, Charpy impact, fracture toughness, fatigue, inter-granular corrosion, SCC testing (U-bend, SSRT), creep. The aim is to compare the austenitic stainless steel (SS 316L) obtained with L-PBF to the conventional SS 316L and to take into account the heterogeneity of material that may occur in a manufacturing and between manufacturers. In this paper, we will focus on the variability and heterogeneity of L-PBF 316L material. For this, tensile samples and charpy impact samples has been produced extensively to cover several orientation axis in the whole volume of the machine capability. The usual physical parameters: hardness, density, chemical composition were also extensively measured.Specific builds have been defined to be representative of the most severe condition (nest factor, high structure…) allowing to catch a real range of properties obtained with L-PBF process. All the four manufacturings were analyzed in terms of Tensile and Resilience properties by CIEMAT partner. Density, metallography and chemical composition were also recorded. This paper is focused specifically on CEA manufacturer, which have the particularity to have worked with two different powder approvals (same specification), the same machine, but two different operators. CEA deviated from the initial manufacturing plan, but also it makes the opportunity to study others parameters (powder approval & human factor). The qualification methodology has been defined with the three others manufacturers (with a same powder batch).The final deliverable at the end of NUCOBAM project (end of 2024) is the Qualification methodology for nuclear-grade L-PBF SS 316L materials & components. This document will provide requirements for all aspects for producing a safety-classified component via L-PBF
Understanding UV-induced degradation mechanisms in SHJ solar cells and their reversibility: The role of hydrogen and doping
No full textInternational audienceSilicon heterojunction solar cells are among the leading PV technologies for high-efficiency modules, but their sensitivity to UV radiation raises durability concerns for outdoor deployment. In this study, we investigate the UV-induced degradation of silicon heterojunction cell precursors by isolating the impact of subcell layers under controlled UVA and UVB irradiations. Our results identify the front hydrogenated amorphous silicon (i/n)a-Si:H layers as key degradation sites, exhibiting significant losses in minority carrier lifetime and iV (>40 mV). Fourier-transform infrared (FTIR) spectroscopy indicated a selective degradation of high stretching mode Si–Hn bonding configurations, creating defects at the c-Si/a-Si:H interface and releasing free hydrogen. These mobile and reactive hydrogen species intensely degrade both passivation mechanisms (chemical and field-effect) by electrically inhibiting dopants via P–H complex formation. Light soaking treatments combining thermal and light activation enable significant passivation and conductivity recovery through hydrogen redistribution, though reversibility diminishes at high UVA doses, indicating a photon-dose-dependent degradation threshold. These findings provide mechanistic insights into UVID pathways and highlight the importance of hydrogen management and UV attenuation strategies for long-term SHJ module reliability
Impact of collective effects on beam stability in the FCC-ee main rings and the high-energy booster
No full textInternational audienceThe electron positron Future Circular Collider (FCC-ee) is considered the primary contender for the next major particle accelerator within the European Strategy for particle physics, aiming to achieve unprecedented luminosities to enable precise measurements of Z, W, and H bosons along with the top quark. Despite its potential, the FCC-ee project faces significant operational and design challenges, especially in managing collective effects such as space charge, wake fields, coherent synchrotron radiation, intra-beam scattering, and beam-beam interactions. The FCC-IS Feasibility Study brings together experts to address these challenges under one umbrella. This paper presents an updated status of the collective effects studies for FCC-ee main ring and high-energy booster, examining their implications and exploring potential mitigation strategies to prevent resulting instabilities
Rotational bands in Md
No full textInternational audienceRotational structures in 249 Md have been observed for the first time. One set of states forms a pair of strongly coupled bands with relatively strong E2 transitions and no identifiable M1 transitions between the two signature partners. Another set of states suggests a decoupled sequence of E2 transitions. These bands are assigned as based on the 7/2−[514] and on the favored signature of the 1/2−[521] Nilsson level, respectively. Based on previous decay studies, these levels are thought to be the ground state and first excited state of 249 Md , which also agrees with theoretical predictions