ELABORATION PAR CROISSANCE CZOCHRALSKI, CARACTERISATION SPECTROSCOPIQUE ET PROPRIETES LASER DE MONOCRISTAUX DOPES PAR L'YTTERBIUM

CETTE ETUDE S'INSCRIT DANS LA RECHERCHE DE NOUVEAUX LASERS SOLIDES POMPES PAR DIODES POUR L'EMISSION AUTOUR DE 1 M. DANS CE CADRE, LES MATERIAUX ACTIVES PAR L'YTTERBIUM OFFRENT DES PERFORMANCES ACCRUES PAR RAPPORT AUX LASERS AU NEODYME. LE CHOIX DE NOUVEAUX MATERIAUX REPOSE SUR PLUSIEURS CRITERES. LE PREMIER EST LEUR FACILITE D'ELABORATION. LA METHODE DE CZOCHRALSKI CONSTITUE UNE TECHNIQUE DE CHOIX POUR OBTENIR DE GROS MONOCRISTAUX D'EXCELLENTE QUALITE OPTIQUE. POUR CETTE RAISON, L'UN DES ASPECTS DE CE TRAVAIL A ETE LA MISE AU POINT D'UNE MACHINE D'ELABORATION DE MONOCRISTAUX. UNE ATTENTION PARTICULIERE A ETE PORTEE A LA REGULATION DE LA CROISSANCE. SUR LE PLAN SPECTROSCOPIQUE, L'ECLATEMENT DU NIVEAU FONDAMENTAL DE L'YTTERBIUM PAR LE CHAMP CRISTALLIN DOIT ETRE SUFFISANT POUR OBTENIR UN FONCTIONNEMENT LASER QUASI-4-NIVEAUX. DE PLUS, UN DESORDRE STRUCTURAL EST SOUHAITABLE POUR ELARGIR LES RAIES DE TRANSITIONS ET AMELIORER L'EFFICACITE DU POMPAGE PAR DIODES. LES COMPOSES RETENUS DANS CETTE ETUDE COMBINENT CES CARACTERISTIQUES. CE SONT LES BORATES M 3TR(BO 3) 3 (M = BA, SR TR = LU, Y) ET CA 3TR 2(BO 3) 4 (TR = Y, GD), ET LES SILICATES Y 2SIO 5(YSO), SRY 4(SIO 4) 3O (SYS) ET CA 2AL 2SI 2O 7 (CAS). L'ETUDE DE L'INFLUENCE DES CONDITIONS DE CROISSANCE A PERMIS D'OBTENIR DANS LA PLUPART DES CAS DES CRISTAUX DE GRANDES DIMENSIONS (PLUSIEURS CM 3) ET DE BONNE QUALITE OPTIQUE. DANS TOUS CES MATERIAUX, LES NIVEAUX D'ENERGIE DE L'YTTERBIUM SONT FORTEMENT ECLATES. L'UTILISATION DU MODELE PCEM PERMET DE CONFIRMER LES DIAGRAMMES DE NIVEAUX D'ENERGIE EXPERIMENTAUX, ET IL EST MONTRE QUE CE MODELE PEUT ETRE EMPLOYE DANS UNE DEMARCHE PREDICTIVE. CELA PERMETTRAIT D'ACCELERER LA DECOUVERTE DE NOUVEAUX MATERIAUX POTENTIELLEMENT INTERESSANTS. ENFIN, L'OSCILLATION LASER A ETE OBSERVEE POUR LA PLUPART DE CES COMPOSES SOUS POMPAGE PAR UN LASER SAPHIR-TITANE, AVEC UN SEUIL GENERALEMENT FAIBLE ET DES RENDEMENTS TRES PROMETTEURS. DE PLUS, L'EMISSION LASER PEUT ETRE ACCORDABLE SUR UNE LARGE GAMME DE LONGUEUR D'ONDE.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

High-temperature contactless viscosity measurements by the gas―film levitation technique: Application to oxide and metallic glasses

International audienceno abstrac

An Efficient, Versatile, and Safe Access to Supported Metallic Nanoparticles on Porous Silicon with Ionic Liquids

The metallization of porous silicon (PSi) is generally realized through physical vapor deposition (PVD) or electrochemical processes using aqueous solutions. The former uses a strong vacuum and does not allow for a conformal deposition into the pores. In the latter, the water used as solvent causes oxidation of the silicon during the reduction of the salt precursors. Moreover, as PSi is hydrophobic, the metal penetration into the pores is restricted to the near-surface region. Using a solution of organometallic (OM) precursors in ionic liquid (IL), we have developed an easy and efficient way to fully metallize the pores throughout the several-µm-thick porous Si. This process affords supported metallic nanoparticles characterized by a narrow size distribution. This process is demonstrated for different metals (Pt, Pd, Cu, and Ru) and can probably be extended to other metals. Moreover, as no reducing agent is necessary (the decomposition in an argon atmosphere at 50 °C is fostered by surface silicon hydride groups borne by PSi), the safety and the cost of the process are improved

Physical investigation of the impact of electrolessly deposited self-aligned caps on insulation of copper interconnects

International audienceWith the miniaturization of ULSI circuits and the associated increase of current density up to several MA/cm2, copper interconnects are facing electromigration issues at the top interface with the dielectric capping layer SiC(N). A promising solution is to insert selectively on top of copper lines a CoWP metallic self-aligned encapsulation layer, deposited using a wet electroless process. We study the impact of this process on electrical line insulation as a function of cap thickness at the 65 nm technology node and we investigate the physical origin of leakage currents. Below a critical thickness, only a slight leakage current increase of less than one decade is observed, remaining within the specification for self-aligned capping layer processes. Above this critical thickness, large leakage currents are generated due to the combined effect of lateral growth and the presence of parasitic redeposited nodules. We show that a simple phenomenological model allows to reproduce the experimental data, to assess quantitatively the contribution of parasitic defects, and to predict that the self-aligned barrier technology should be extendible up to the 32 nm node, provided that a thin cap layer of less than 8 nm is used

Magnetic, Structural, and Chemical Properties of Cobalt Nanoparticles Synthesized in Ionic Liquids

International audienc

Electrochemical Behavior of Copper in Post-Via-Etch Cleaning Solutions

International audienceThe actions of glycolic acid and BTA on copper have been investigated by electrochemical methods. Different concentrations in glycolic acid were investigated: 1%wt, 2%wt, 3%wt and 4%wt. Results show that the cleaning action of glycolic acid results from smooth corrosion of the metal. Copper dissolution increases with glycolic acid concentration due to the formation of a copper complex which precedes copper dissolution. In the presence of BTA, a corrosion inhibitor of copper, a [Cu(I)BTA] complex is formed on the surface which blocks copper dissolution. In a mixture of glycolic acid and BTA (1%wt/ 0.1%wt), an intermediary behavior is observed. A competitive action occurs between the film formation due to the interaction between BTA and copper and the superficial etching of the metal by glycolic acid which removes the inhibitor-copper film

Direct extraction of platinum nanoparticles from fuel cells with ionic liquids: Part 1. Implementation and optimization of the process parameters

International audienceThe cost of proton-exchange membrane fuel cell (PEMFCs) comes mainly from the platinum nanoparticles, which are used as catalyst; it represents 40 % of the stack price for a large-scale production. It is thus crucial to reduce their cost to produce cheaper devices, which could compete with fossil energy on the industrial market. One way to reach this goal would be to recover the Pt catalyst from the membrane electrode assembly (MEA) for further recycling. For now, current end-of-life (EoL) technologies are mainly based on hydrometallurgical and pyro-hydrometallurgical processes for recovering platinum which are identified to be energy demanding generate high amounts of toxic liquids and gaseous effluents. To meet sustainability and circular economy criteria in the recycling of noble metals, our approach was based on the use of ionic liquids (ILs) to both extract and stabilize platinum in the form of metallic nanoparticles (Pt NPs), thus avoiding the emissions of hydrofluoric acid (HF) and the use of strong acids, which make the waste management of conventional processes complicated. Thirteen different ILs were selected to investigate how their structural composition as well as their physico-chemical properties may affect the extent of Pt extraction, and their ability to stabilize detached nanoparticles. This screening study showed that ionic liquids could interact with all the elements of the active layer and allowed us to delineate the key parameters that ILs should possess to achieve the best extraction performance: hydrophilicity, the hydrogen bonding ability, the coordinating ability of the anions.The best result was obtained with the trihexyltetradecylphosphonium chloride (P66614Cl) (commercial Cyphos® IL 101) (120 °C and 6 h) which not only led to an extraction extent up to > 90 % of the Pt present initially on the catalytic layer, but also allowed in a single step to detach the Pt NPs from the carbon support. The metallic Pt NPs suspended in P66614Cl were found stable with diameter around 2-3 nm as evidenced by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) analyses. Compared to conventional processes, this safer and convenient route to recover Pt catalyst from MEAs directly in their metallic form by simple immersion of the electrode in the appropriate IL opens up new perspectives in term of rare earth metal recycling from material composites

PROCÉDÉ DE RÉCUPÉRATION DE PARTICULES DE PLATINOÏDE CONTENUES DANS UN SUPPORT ÉLECTRIQUEMENT ISOLANT

Procédé de récupération de particules (122) de platinoïde contenues dans un support électriquement isolant, le procédé comprenant une étape d'extraction au cours de laquelle le support électriquement isolant contenant les particules de platinoïde est plongé dans une solution liquide ionique comprenant un premier liquide ionique, de manière à extraire les particules (122) de platinoïde du support électriquement isolant

Impact of Surface Chemistry on Copper Deposition in Mesoporous Silicon

CAPLUS AN 2016:1100917(Journal; Online Computer File)An easy, efficient, and safe process is developed to metalize mesoporous Si (PSi) with Cu from the decompn. of a soln. of mesitylcopper (CuMes) in an imidazolium-based ionic liq. (IL), [C1C4Im][NTf2]. The impregnation of a soln. of CuMes in IL affords the deposition of metallic islands not only on the surface but also deep within the pores of a mesoporous Si layer with small pores <10 nm. Therefore, this process is well suited to efficiently and completely metalize PSi layers. An in-depth mechanistic study shows that metal deposition is due to the redn. of CuMes by surface silane groups rather than by Si oxidn. as obsd. in aq. or H2O-contg. media. This could open a new route to the chem. metalization of PSi by less-noble metals difficult to attain by a conventional displacement reaction. [on SciFinder(R)