65 research outputs found

    Two components for one resistivity in LaVO3/SrTiO3 heterostructures

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    A series of 100 nm LaVO3 thin films have been synthesized on (001)-oriented SrTiO3 substrates using the pulsed laser deposition technique, and the effects of growth temperature are analyzed. Transport properties reveal a large electronic mobility and a non-linear Hall effect at low temperature. In addition, a cross-over from a semiconducting state at high-temperature to a metallic state at low-temperature is observed, with a clear enhancement of the metallic character as the growth temperature increases. Optical absorption measurements combined with the two-bands analysis of the Hall effect show that the metallicity is induced by the diffusion of oxygen vacancies in the SrTiO3 substrate. These results allow to understand that the film/substrate heterostructure behaves as an original semiconducting-metallic parallel resistor, and electronic transport properties are consistently explained.Comment: Improved version as accepted in Journ Phys: Cond Mat. Additional Optical measurements are presente

    SiNx:Tb3+--Yb3+, an efficient down-conversion layer compatible with a silicon solar cell process

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    SiN x : Tb 3+-Yb 3+, an efficient down-conversion layer compatible with silicon solar cell process Abstract Tb 3+-Yb 3+ co-doped SiN x down-conversion layers compatible with silicon Photovoltaic Technology were prepared by reactive magnetron co-sputtering. Efficient sensitization of Tb 3+ ions through a SiN x host matrix and cooperative energy transfer between Tb 3+ and Yb 3+ ions were evidenced as driving mechanisms of the down-conversion process. In this paper, the film composition and microstructure are investigated alongside their optical properties, with the aim of maximizing the rare earth ions incorporation and emission efficiency. An optimized layer achieving the highest Yb 3+ emission intensity was obtained by reactive magnetron co-sputtering in a nitride rich atmosphere for 1.2 W/cm2{}^2 and 0.15 W/cm2{}^2 power density applied on the Tb and Yb targets, respectively. It was determined that depositing at 200 {\textdegree}C and annealing at 850 {\textdegree}C leads to comparable Yb 3+ emission intensity than depositing at 500 {\textdegree}C and annealing at 600 {\textdegree}C, which is promising for applications toward silicon solar cells.Comment: Solar Energy Materials and Solar Cells, Elsevier, 201

    Electroluminescence efficiencies of erbium in silicon-based hosts

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    International audienceWe report on room-temperature 1.5 lm electroluminescence from trivalent erbium (Er3þ) ionsembedded in three different CMOS-compatible silicon-based hosts: SiO2, Si3N4, and SiNx. We showthat although the insertion of either nitrogen or excess silicon helps enhance electrical conductionand reduce the onset voltage for electroluminescence, it drastically decreases the external quantumefficiency of Er3þ ions from 2% in SiO2 to 0.001% and 0.0004% in SiNx and Si3N4, respectively.Furthermore, we present strong evidence that hot carrier injection is significantly more efficient thandefect-assisted conduction for the electrical excitation of Er3þ ions. These results suggest strategiesto optimize the engineering of on-chip electrically excited silicon-based nanophotonic light sources

    Réalisation d’un laser à faible courant de seuil, avec des boites quantiques InAs/InP organisées et couplées latéralement

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    Nous présentons ici la réalisation d’un laser à faible courant de seuil avec des boites quantiques (QDs) organisées et couplées InAs/InP sur subsstrat (311)B pour une émission à 1.55 m. En effet, pour des hautes densités de QDs, une organisation périodique apparaît dans le plan. Cette organisation renforce le couplage latéral inter-boites. Des expériences de magnéto-photoluminescence permettent de mettre en évidence ces effets de couplage. Ce couplage améliore l’injection des porteurs. Une émission laser avec des faibles courants de seuil est obtenue avec de telles boites

    Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

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    IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

    Apport du Heidelberg Retina Tomograph II Rostosk Cornea Module (HRT II RCM) pour l'étude de la surface oculaire

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    De nouveaux systèmes de microscopie confocale in vivo comme le Heidelberg Retina Tomograph II Rostock Cornea Module (HRT II RCM) permettent aujourd hui une analyse de l ensemble de la surface oculaire du centre à la périphérie mais aussi des tissus les plus superficiels jusqu aux plus profonds. L analyse de la conjonctive est désormais possible avec des applications multiples comme l évaluation de la cicatrisation après chirurgie du glaucome. Par une meilleure résolution, une plus grande rapidité d acquisition et un traitement informatique des images simplifié, cette technique d exploration s est révélée extrêmement prometteuse pour l exploration des pathologies cornéennes. Cette approche in vivo, quasi-histologique et facilement accessible aux cliniciens des très nombreuses pathologies de la surface oculaire constitue une aide précieuse dans leur prise en charge. Enfin en recherche, cette technique non invasive et simple ouvre de très nombreuses perspectives dans le domaine de l expérimentation animale. L analyse en microscopie confocale in vivo de la cornée, mais aussi maintenant de l ensemble de la surface oculaire normale et pathologique ne fait donc que commencer.PARIS6-Bibl.Pitié-Salpêtrie (751132101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

    Transfert d énergie entre nanoclusters de Silicum et Erbium dans des matrices oxydes et nitrures de Si (applications à des diodes électroluminescentes)

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    Ce travail de thèse est basé sur l analyse et l optimisation d un matériau alternatif aux interconnexions métalliques des circuits intégrés. Ce matériau est une matrice de SiO2 contenant des nanoclusters de silicium (nc-Si) et des ions erbium (Er3+). Grâce à un transfert d énergie entre nc-Si et Er3+, la forte absorption des nc-Si dans la gamme du visible permet l excitation indirecte des ions Er3+ qui émettent ensuite à 1,5 m. L objectif est d optimiser les propriétés d émission de l erbium à 1,5 m, et pour ce faire de maximiser le transfert entre nc-Si et Er3+. Dans un premier temps les travaux sont axés sur les traitements thermiques pendant et après le dépôt. Ensuite, nous analysons l effet de l épaisseur de la couche mince sur les propriétés optiques du matériau et nous montrons que les couches très minces (< 150 nm) présentent un manque de sensibilisateurs qui réduit le nombre d erbium excités. Nous démontrons alors que ce problème peut être résolu en augmentant la concentration en silicium, augmentant ainsi le nombre de sensibilisateurs au sein des couches les plus minces. Il est ensuite montré que les ions Er3+ bénéficient d une excitation multi-niveaux par les sensibilisateurs nc-Si. Une deuxième partie du travail de thèse consiste à réaliser des diodes électroluminescentes (DELs) et à en optimiser l émission à 1,5 m. Nous montrons qu épaisseur et excès de silicium doivent êtres choisi conjointement pour l optimisation des propriétés optiques et électriques des DELs. Une dernière partie montre que les propriétés des DELs peuvent êtres améliorés par l utilisation de matrices hôtes oxynitrures et nitrures pour les nc-Si et Er3+.This work is based on the analysis and optimization of an alternative material to replace metallic interconnections of integrated circuits. This material is an SiO2 matrix containing Silicon-nanoclusters (Si-nc) and Erbium ions (Er3+). Thanks to an energy transfer between Si-nc and Er3+, the strong absorption of Si-nc in the visible range results in the indirect excitation of Er3+ ions that thus emit at 1.5 m. The goal is to optimize the emission properties of Er3+ at 1.5 m, and for that, to maximize the energy transfer between Si-nc and Er3+. First, the work is directed on thermal treatments during and after the deposition. Then, we analyze the influence of the film thickness on the material s optical properties and we show that thinnest films (< 150 nm) contain a low number of that reduces the number of excited erbium. We demonstrate that this problem can be overcome by increasing the silicon concentration, hence raising the number of sensitizers for Er3+. It is also shown that Er3+ ions benefit from a multilevel excitation by Si-nc sensitizers. A second part of the work consists in the realization of light-emitting diodes (LEDs) and to optimize their emission at 1.5 m. We show that thickness and silicon excess must be chosen concomitantly to optimize optical and electrical properties of LEDs. In a last part we show that LEDs properties can be enhanced using nitrogen-based matrices like oxynitrides or nitrides as hosts for Er3+.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF
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