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Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2007-2008. / The processes of generalized and localized corrosion induced at a cobalt electrode polarized in slightly alkaline aqueous media (pH 7-10) have been investigated using electrochemical methods and surface analysis techniques. In buffer solutions of H2C03/HCO,/CO^ at near neutral pH (7-8), particularly aggressive corrosion phenomena have been observed. The presence of carbonic acid in solution, as well as the high solubility of the CoO oxide, were identified as being responsible for the accelerated metal dissolution. However, the addition of a low concentration of phosphate species to the corrosive environment allows an important inhibition of cobalt dissolution under the form of the Co(CO,)2_ soluble complex. Potentiodynamic experiments have shown the efficiency of benzotriazole to inhibit the active dissolution of cobalt in slightly alkaline media. Using a novel approach to obtain the SERS effect (Surface-Enhanced Raman Scattering) directly from a massive cobalt electrode, the interaction mode of benzotriazole with the metal surface has been determined. Neutral benzotriazole molecules, first chemisorbed under cathodic polarization, are thereafter deprotonated at the zero charge potential of the System. As a result, a thin polymer-like [Co(II)(BTA)2-H20]„ film, insoluble and highly protective, is found on the electrode surface. This passive film restrains the access of chemical species known to be aggressive to the active sites of the electrode. In a situation of incomplete surface coverage by benzotriazole, cobalt species which originate from further dissolution processes, are preferentially complexed to deprotonated benzotriazole species present in the bulk solution. Such a mechanism contributes to the formation of the [Co(II)(BTA)2H20]„ film. To avoid degradation of cobalt through the initiation of localized corrosion induced by chloride ions, a protection method based on the passivation of the metal has been developed. It has been demonstrated that when cobalt is submitted to specific potentiostatic conditions, a passive bilayer film composed of CoO and C03O4 is electrogenerated on the metal surface. The uniform color of that film, attributed to iridescence, shows that the layer has a constant thickness ail over the electrode surface. A complete characterization of the optical and physical properties of that film is presented. / The processes of generalized and localized corrosion induced at a cobalt electrode polarized in slightly alkaline aqueous media (pH 7-10) have been investigated using electrochemical methods and surface analysis techniques. In buffer solutions of H2C03/HCO,/CO^ at near neutral pH (7-8), particularly aggressive corrosion phenomena have been observed. The presence of carbonic acid in solution, as well as the high solubility of the CoO oxide, were identified as being responsible for the accelerated metal dissolution. However, the addition of a low concentration of phosphate species to the corrosive environment allows an important inhibition of cobalt dissolution under the form of the Co(CO,)2_ soluble complex. Potentiodynamic experiments have shown the efficiency of benzotriazole to inhibit the active dissolution of cobalt in slightly alkaline media. Using a novel approach to obtain the SERS effect (Surface-Enhanced Raman Scattering) directly from a massive cobalt electrode, the interaction mode of benzotriazole with the metal surface has been determined. Neutral benzotriazole molecules, first chemisorbed under cathodic polarization, are thereafter deprotonated at the zero charge potential of the System. As a result, a thin polymer-like [Co(II)(BTA)2-H20]„ film, insoluble and highly protective, is found on the electrode surface. This passive film restrains the access of chemical species known to be aggressive to the active sites of the electrode. In a situation of incomplete surface coverage by benzotriazole, cobalt species which originate from further dissolution processes, are preferentially complexed to deprotonated benzotriazole species present in the bulk solution. Such a mechanism contributes to the formation of the [Co(II)(BTA)2H20]„ film. To avoid degradation of cobalt through the initiation of localized corrosion induced by chloride ions, a protection method based on the passivation of the metal has been developed. It has been demonstrated that when cobalt is submitted to specific potentiostatic conditions, a passive bilayer film composed of CoO and C03O4 is electrogenerated on the metal surface. The uniform color of that film, attributed to iridescence, shows that the layer has a constant thickness ail over the electrode surface. A complete characterization of the optical and physical properties of that film is presented. / Les processus de corrosion généralisée et localisée induits à une électrode de cobalt polarisée en milieux aqueux faiblement alcalins (pH 7-10) ont été étudiés à l'aide de méthodes électrochimiques et de techniques d'analyses de surface. Dans des solutions tampons H^CO^/HCOj/CO, de pH quasi-neutres (7-8), des phénomènes de corrosion particulièrement agressifs ont été observés. La présence d'acide carbonique dans la solution, de même que la grande solubilité de l'oxyde CoO dans ces conditions de pH, ont été identifiées comme étant responsables de la dissolution accélérée du métal. Toutefois, l'ajout d'une faible concentration de phosphates dans le milieu corrosif permet d'inhiber considérablement la mise en solution du cobalt sous la forme de l'ion soluble complexe Co(C03)*\ Des expériences potentiodynamiques ont démontré l'efficacité du benzotriazole à inhiber la dissolution active du cobalt en milieux faiblement alcalins. En développant une nouvelle voie d'obtention de l'effet SERS (Surface-Enhanced Raman Scattering) directement à partir d'une électrode de cobalt, le mode d'interaction du benzotriazole avec la surface métallique a été déterminé. Les molécules neutres de benzotriazole, d'abord chimisorbées sous polarisation cathodique, sont déprotonnées au potentiel de charge nulle du système. 11 en résulte la formation d'un mince film polymérique du type [Co(Il)(BTA)2-H20]„, insoluble et hautement protecteur, qui bloque l'accès des espèces réputées agressives aux sites actifs de l'électrode. Dans une situation de recouvrement de surface incomplet par le benzotriazole, les espèces de cobalt issues des processus de corrosion subséquents sont préférentiellement complexées par les espèces de benzotriazole déprotonnées et présentes en solution, consolidant ainsi la formation du film de [Co(II)(BTA)2H20]„. Afin de lutter contre la détérioration du cobalt via l'initiation de la corrosion localisée induite par les ions chlorures, une voie de protection par passivation du métal a été mise en place. En soumettant le cobalt à des conditions potentiostatiques particulières, un film passivant composé d'une bicouche de CoO et de C03O4 a pu être électrogénéré à la surface du métal. La coloration uniforme de ce film, attribuée à un phénomène d'iridescence, montre que la couche est d'épaisseur constante sur toute la surface de l'électrode. Une caractérisation complète des propriétés optiques et physiques de ce film est présentée.

Call number: LD2668 .T4 1959 J64

published_or_final_version / Physics / Master / Master of Science

Electrolessly deposited CoWP capping layers have been demonstrated to effectively reduce electromigration of Cu at the interconnect/dielectric-barrier cap interface while reducing resistivity relative to SiCN. However, as device dimensions scale, the need for alternative methods for the selective deposition of sub-5 nm, ultrathin, conformal Co capping layers is apparent. To develop methods for area-selective atomic layer deposition (AS-ALD) of Co caps for next-generation Cu interconnects, the ALD behavior of bis(N-tert-butyl-N’-ethylpropionamidinato) cobalt(II) (CoAMD) is evaluated on Cu, SiO₂, and a porous low-k ( ~2.6) dielectric, CDO. The first and second ALD half reactions of CoAMD on the respective substrates is evaluated with H₂ coreactant by adsorbing the precursor on the substrates under ALD cycling conditions at 265 °C with and without coreactant exposure. The adsorption studies indicate that CoAMD preferentially deposits most on Cu and least on CDO. Further, CoAMD, like other amidinate precursors, readily dissociates on the Cu transition metal surface but the ultimate per-cycle coverage is self-limited by the slow desorption of amidinate ligands and fragments from the Cu surface. Co films deposited by ALD from CoAMD on Cu at 265 °C indicate that Co burrows into the lower energy Cu surface as the film grows in order to reduce the free surface energy. The Cu remains as a surfactant-like layer on the topmost Co surface up to film thicknesses of at least 16 nm. Moreover, considerable intermixing at the Co/Cu interface and Cu concentration several nm into the Co films are observed indicating high surface mobility of the two materials and Cu diffusion at polycrystalline Co grain boundaries. Finally, employing low-tempurature ALD and selectively passivating the dielectric surfaces with OH targeting passivants leads to enhanced selectivity of CoAMD for deposition on Cu versus SiO₂ and CDO. Depositing Co from CoAMD on Cu and CDO at 165 °C after 500 kTorr-s exposure to trimethylchlorosilane at 50 °C leads to a 30:1 preference for Co accumulation on Cu, a twelve times improvement compared to deposition on cleaned Cu and CDO at 265 °C. / text

The aim of the work carried out in this thesis is to develop new efficient catalytic systems for the synthesis of enantioenriched secondary alcohols. The access to this class of important synthetic intermediates is possible either by nucleophilic addition of organometallic reagents to aldehydes or by reduction of prochiral ketones catalysed with chiral complexes. We have thus developed two new catalytic systems for the asymmetric hydrosilylation of ketones using polymethylhydrosiloxane (PMHS) as an inexpensive reducing agent. A first approach is based on the synthesis of new N, S ligands and zinc complexes bearing a ferrocenyl backbone with planar chirality. Those compounds were prepared and evaluated first in the addition of diethyl zinc to aldehydes, reaching enantiomeric excesses up to 74%. The precatalysts were also evaluated in the reduction of prochiral ketones with PMHS. In that case, a good reactivity was observed and enantioselectivities up to 61% could be reached. It is assumed that a zinc hydride complex formed by thermal ß-elimination of the corresponding ethyl complex is the active species. This catalytic system also allows the hydrosilylation of dialkyl ketones, a challenging goal in asymmetric catalysis. In a second part of this work, we have developed a new catalytic system for hydrosilylation of ketones based on the hypothetical formation of a chiral cobalt hydride catalyst. This intermediate is supposed to be formed by reaction of the corresponding neutral cobalt (II) complex with tetrabutyl ammonium triphenyldifluorosilicate (TBAT) as activator and a silane. Following a preliminary screening, salen type ligands were found to be the most efficient when activated with TBAT in presence of PMHS. Modifications on this structure by replacing the phenol group of the ligand by various sulfonamide groups led, after optimisation of the reaction parameters, to a highly efficient catalytic system with enantioselectivities reaching 84 % for the reduction of tetralone. This work should thus open new perspective for the design of highly enantioselective and low cost catalytic systems for the hydrosilylation of prochiral ketones.

Glyphosate (N-(phosphonomethyl)glycine) is the phytotoxic reagent in the widely used Roundup® herbicide. Its mode of action in plants is the disruption of the Shikimate pathway, part of an important route to the biosynthesis of essential aromatic amino acids. It is well documented that glyphosate can be degraded by soil microorganisms after contact of the herbicide solution with the soil. It is also accepted that glyphosate, an excellent ligand, is readily absorbed to metal ions, such as Fe(III), that can be abundant in soils. There have been many accounts on the microbial degradation of glyphosate, and several metal-glyphosate complexes have been synthesised and characterised. Surprisingly, given the degree of adsorption to metal ions in the soil, there have not, to date, been any reports in the literature on the reactivity of metal-glyphosate complexes. The behaviour of these types of complexes under various reaction conditions may give us an insight into the mechanisms present when glyphosate degrades. In order to explore the behaviour of metal-glyphosate adducts, we have prepared several new cobalt-PMG complexes in the lab. These complexes have been characterised by NMR, mass spectrometry, elemental analysis, and in some cases X-ray crystal structure determination. We chose to synthesise complexes where the PMG ligand is bidentate or tridentate, filling the remaining four or three (respectively) coordination sites with an ancillary, nitrogen-containing ligand. We have subjected the complexes to photolytic and basic conditions, as we are interested in ascertaining how coordinated PMG might behave when irradiated with UV light, and when it is C-deprotonated. Metal-glyphosate complexes in nature may be exposed to UV light, so we are concerned with how the coordinated ligand might react under these circumstances. We have found that the prepared cobalt-PMG complexes are reactive when exposed to UV light, and that this appears to result in the degradation of the complex, and in some cases, the PMG ligand itself. The reactivity of C-deprotonated PMG is also an area of interest to us. It is possible that elevations in soil pH can lead to C-deprotonation of glyphosate, then further reactivity that may contribute to the degradation of the compound. Furthermore, when the herbicide is held in the active site of an enzyme within a microbe, it may become deprotonated, and this may aid in its microbial degradation. We have found that, under basic conditions, the reactivity of the prepared PMG complexes depends on the ancillary ligand attached - π-acidic, pyridine-containing ancillary ligands appear to increase the reactivity of coordinated PMG. It seems that amine-containing ligands hinder the reactivity of the coordinated PMG such that the complex remains intact. It is hoped that the results of the research described in this thesis will assist in the future investigations into the reactivity of the herbicide glyphosate.

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