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

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

International audienc

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)

Gap fill enhancement with medium acid electrolyte for the 45nm node and below

International audienceCopper damascene interconnects technologies have introduced the use of electroplating in semiconductor. Several specific issues were brought by this typical application such as the necessity to plate in very narrow features and on large substrates while keeping electrical contacts on the edges. For this, sulfate based acidic solution coupled with additives allowing superfill behavior were introduced. Since the introduction of 200mm wafers, acidity of the bath was chosen as a compromise between transport efficiency and sufficient resistivity to ensure good plating uniformity on large diameters. Going to sub 65nm technologies, so called "1ow acid" electrolytes are supposed to reach their limits. In order to enhance the gap fill properties, medium acid electrolytes are being evaluated. In this study, the performances of such electrolytes are examined, first using coupons to evaluate the deposition kinetics compared to a low acid one. In order to have a first cross evaluation of their performances in integration, electrical tests are realized on 45nm node technology 300mm wafers

Effect of surface chemistry on the electrical double layer in a long-chain ionic liquid

International audienceRoom temperature ionic liquids (ILs) can create a strong accumulation of charges at solid interfaces by forming a very thin and dense electrical double layer (EDL). The structure of this EDL has important consequences in numerous applications involving ILs, for example in supercapacitors, sensors and lubricants, by impacting the interfacial capacitance, the charge carrier density of semiconductors , as well as the frictional properties of the interfaces. We have studied the interfacial structure of a long chain imidazolium-based IL (1-octyl-3-methylimidazolium dicyanamide) on several substrates: mica, silica, silicon and molybdenum disulfide (MoS 2), using atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. We have observed 3 types of interfacial structures for the same IL, depending on the chemistry of the substrate and the water content, showing that the EDL structure is not an intrinsic property of the IL. We evidenced that at a low water content, neutral and apolar (thus hydrophobic) substrates promote a thin layer structure, where the ions are oriented parallel to the substrate and cations and anions are mixed in each layer. In contrast, a strongly charged (thus hydrophilic) substrate yield an extended structuration into several bilayers, while a heterogeneous layering with loose bilayer regions was observed on an intermediate polar and weakly charged substrate and on an apolar one at a high bulk water content. In the latter case, water contamination favors the formation of bilayer patches by promoting the segregation of the long chain IL into polar and apolar domains