The aims of this work were two-fold - to enhance the 'latent functionality' of a silicon centre by expanding the range of functionalisation reactions available to such compounds, and to develop novel silicon-tethered transformations in order to increase the utility of this attractive synthetic strategy. 1. Aryle Silane Oxidation. Building upon the earlier work of Tamao and co-workers, we have developed a mild, functional group-tolerant oxidation of arylsilanes, allowing a wide range of phenols to be readily accessed. One key insight uncovered during this work was the observation that this oxidation could be acheived with sub-stoichiometric quantities of a fluoride promoter, thus allowing several TBS-protected substrates to be oxidised without any concomitant loss of the protecting group. 2. Silicon-Tethering Methodology. In order to utilise our recently acquired expertise in the field of alkoxy arylsilane synthesis, we sought to develop a novel silicon-tethered iron-catalysed biaryl coupling. Unfortunately, despite our considerable efforts, this methodology was found to suffer from reproducibility issues, and thus our attentions subsequently turned to silicon-tethered palladium- and platinum-catalysed processes. These investigations proved to be more fruitful, with the palladium-catalysed methodology affording a small range of silicon-tethered products. Finally, a novel platinum-catalysed hydro-silylation/electrocyclisation cascade was also developed, allowing a substituted arene to be accessed from a dienyne precursor.

This thesis describes the study of a series of platinum complexes, with particular emphasis towards hydrosilation. Platinum bis(phosphine) azodicarbonyl complexes Pt(PRI 3)2(R20CNNCOR2) (RI = Ph, Me; R2 = Ph, Me, OEt, Pri) were synthesised and studied. Multinuclear NMR spectroscopy on Pt(PRI3)2(R20CNNCOR2) revealed that the dicarbonyl substituted azo ligand is co-ordinated asymmetrically, consistent with a five membered, Pt-N-N-C-O ring. The crystal structure of Pt(PPh3)2(Pri02CNNC02Pri) shows that the co-ordination sphere of platinum is essentially square planar and co-planar with the five-membered, Pt(1)-0(1)-C(5)-N(2)-N(1) ring. The Pt(PRI 3)lR20CNNCOR2) complexes show sensitivity towards chlorinated solvents (CH2CI2, CHCI3) under photolysis conditions forming the corresponding platinum bis(phosphine) dichloride complexes; the same products are formed in a slower thermal reaction but only for complexes with azodicarboxylate ligands. Complexes with azodicarboxylate ligands also react photochemically with ethylene in ds-THF yielding Pt(PPh3)2(C2H4) but the azodiacyl analogues are inert in this respect. Azodicarboxylate compounds R02CNNC02R (R = Et, Pri, But) are inhibitors of the catalytic activity of [(Pt {174 _(CH2=CHSiMe2hO }h {.u-( CH2=CHSiMe2)20}] for the hydrosilation reaction. The inhibited species can be decomposed thermally or photoch~mically to give active hydrosilation catalysts. It was found that the bulky azo compound But02CNNC02But was the least effective inhibitor of [(Pt{ 174 - '(CH2=CHSiMe2hO} )2(P-( CH2=CHSiMe2)20)]. The photochemistry of platinum bis(phosphine) malonates and phthalates was found to be limited, and their reactivities were much lower compared to the analogous oxalate complexes. Silyl hydride complexes, cis-Pt(PCY3)2(H)(SiR3), were synthesised from the reaction of Pt(PCY3)2 and the corresponding silane. These complexes were undergo dynamic exchange in solution. Two exchange processes were identified; the first involves mutual phosphine exchange, i.e. positional interchange between the hydride and the silyl ligands. The second process occurs at higher temperatures (above 290 K) and involves the elimination and re-addition of the silane ligand HSiR3. Thermodynamic and activation parameters are obtained for cis-Pt(PCY3)2(SiR3) (R = Ph, SiR3 = SiMe2CH2CH=CH2, SiMe2Et). The reaction of Pt(PCY3)2 with the disilane HSiMe2(l,2-C6~)SiMe2H is thought to form a Pt(IV) bis(silyl) dihydride trigonal bipyramidal species of the form, Pt(PCY3)(H)2[SiMe2(1,2-C6~)SiMe2]' where the hydride ligands are in the axial positions. All of the platinum silyl hydride complexes studied degrade thermally to form trans-Pt(PCY3)2(H)2 at, or above, room temperature.

The intent of this investigation was to directly measure the amount of carbon contamination in a single silicon crystal and, in so doing, develop a mathematical procedure that would be applicable to other contaminants in other substances.

Evidence is presented that apparent silene products obtained from the metalation of cyclopentadienyldimethyl - chlorosilane either with tert-butyl1ithium or with methylenetriphenylphosphorane actually arise from the metalated starting material, a silenoid, rather than from a silafulvene intermediate. Trimethylmethoxysi1ane is shown to be an effective trap for dimethylsilafulvene. A new dimethylsilafulvene precursor, bis(dimethylmethoxysi1yl) cyclopentadiene, which gives high yields of dimethyldimethoxysi1ane and the silafulvene at temperatures as low as 240°C is reported.

When E- or Z-l-methyl-l-phenyl-2-neopentylsilene was generated by the retro-Diels-Alder vacuum-sealed tube thermolysis of its corresponding anthracene adduct, in the presence of various alkoxysilanes, only one diastereomeric adduct was formed in each case, showing that the reactions are stereospecific. An x-ray crystal structure of the methoxytriphenylsilane adduct of the E-silene confirmed its relative configuration as (R,S) or (S,R). This demonstrated that the addition of alkoxysilanes to silenes is stereospecific and syn. The relative configurations of similar alkoxysilane and alkoxystannane adducts to E- and Z-l-methyl-l-phenyl-2-neopentylsilene were assigned based on a combination of xray structures and *3C NMR data. A strong, nonbonded oxygen-metal interaction is apparent in all of those compounds studied. Treatment of the alkoxystannane adducts with alkyl lithium reagents results in tin-lithium exchange in some cases. The results indicate that the resulting <x-lithio alkoxysilanes are not configurationally stable in either THF or hydrocarbon solvents. The reaction of tert butyl lithium with a-trimethylsilylvinylmethylphenylchlorosilane in hydrocarbon solvents yields E- and Z-l-methyl-l-phenyl-2-neopentyl-2-trimethylsilylsilene. In the absence of any traps these silenes undergo a novel tert butyl lithium catalyzed rearrangement to 2-phenyl-3-trimethylsilyl-5,5-dimethyl-2-silahex-3-ene. These silenes were also trapped as their [4+2] cycloadducts with anthracene. The Z-isomer of the anthracene adduct was separated and its stereochemistry confirmed by an x-ray crystal structure. The anthracene adducts of both E- and Z-l-methyl-1-phenyl-2-neopentyl-2-trimethylsilylsilene undergo a facile, stereospecific decomposition at temperatures as low as 190°C to regenerate their respective silenes, the mildest stereospecific route to a silene yet reported. The E- and Z-silenes react stereospecifically with methanol under vacuum-sealed tube conditions. The stereochemistry of the addition is syn and a common mechanism is proposed for the addition of alcohols and the addition of alkoxysilanes to silenes.

The silicon based sensor is able to detect part per trillion ionic silver in 0.0098% hydrofluoric acid based on the open circuit potential (OCP) measurement. The OCP jump of 100 ppt ionic silver solution is up to 120 mV. The complex agent can effectively suppress the ionic silver concentration and suppress the OCP signal. The ability of complex agent to suppress the OCP signal depends on the formation constant of the complex with silver. The complex adsorbed on the sensor surface induces a second OCP jump, the height of the second jump depends on the formation constant of the complex. The MINEQL chemical equilibrium modeling program is used to calculate the ionic silver concentration when complex agent presents, a discrepancy is found between the MINEQL simulation result and the OCP signal of the silicon based sensor. The toxicity of ionic silver to C. dubia is studied parallel to the OCP signal of silicon based sensor. Less toxicity is found when the complex agent is present similar to the OCP signal. Another discrepancy is found between the MINEQL simulation and the toxicity test when MINEQL simulation is used to predict and control the ionic silver concentration. The data from both biosensor C. dubia and silicon based sensor support each other and both are not in agreement with MINEQL simulation prediction.

Cette thèse porte sur une étude expérimentale et théorique de surfaces micro-structurées de silicium, obtenues par traitement dans un plasma SF6/02 à des températures cryogéniques. La texturation qui résulte de ce traitement confère à ces surfaces des propriétés remarquables. L'une d'entre elles est la capacité de piéger et absorber la lumière, qui se traduit par une couleur noire de ces surfaces, d'où l'appellation Black Silicon. Cette propriété qu'on retrouve dans la gamme spectrale du visible et du proche infra-rouge, présente un intérêt particulier pour la conversion d'énergie solaire, aussi bien par voie photovoltaïque que par voie photo-thermique. L'étude que nous avons menée a toutefois porté sur une gamme spectrale plus large, s'étendant jusqu'aux Térahertz. A cet effet, différentes techniques de caractérisation spectrales ont été mises en œuvre. L'analyse des résultats a été effectuée également au moyen de simulations électromagnétiques. Des corrélations ont été mises en évidence entre les propriétés optiques et les caractéristiques morphologiques des surfaces micro-structurées. L'analyse d'images prises au microscope électronique a permis d'esquisser une théorie pour tenter d'expliquer le mécanisme de formation des microstructures de Black Silicon. Enfin, un microcomposant a été réalisé en vue de mettre en œuvre le premier volet applicatif de ce travail. Il s'agit d'un dispositif de conversion photo-thermique qui incorpore des thermo-résistances en platine sur une surface de Black Silicon réalisée sur une membrane thermiquement isolée / This thesis deals with an experimental and theoretical study of micro-structured silicon surfaces, obtained by processing in SF6/02 plasma at cryogenic temperatures. Texturing which results from this treatment gives remarkable properties to these surfaces. One of them is the ability to trap and absorb light, resulting in a black color of the surface, hence the name of Black Silicon. This property that we find in the visible and near infrared spectral ranges, is of particular interest for solar energy conversion, both through photovoltaic and photo-thermal means. The study that we conducted, however, covered a much wider spectral range, extending to the Terahertz. For this purpose, different spectral characterization techniques have been implemented. Analysis of the results was also done using electromagnetic simulations. Correlations were found between the optical and morphological characteristics of micro-structured surfaces. The analysis of images taken by electron microscopy allowed sketching a theory attempting to explain the mechanism of formation of the microstructures of Black Silicon. Finally, a micro-component has been fabricated towards implementing the first part of this application work. It is a photo-thermal conversion device that incorporates platinum thermo-resistance on a surface of Black Silicon, realized on a thermally insulated Silicon membrane

The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, > 8m(2) effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e. g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.

Call number: LD2668 .T4 1950 W56 / Master of Science

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Johannesburg, 2015. / In this thesis electron transport properties of silicon nanowires are studied. The devices are synthesized using a laser ablation technique. The catalysts used in the synthesis are nickel nanoparticles. The silicon nanowires are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Dielectrophoresis is used to align and contact nanowires across two electrodes to create two-terminal devices. In addition four-terminal devices are fabricated using PMMA lift-off based electron beam lithography. Electron transport properties of the fabricated devices have been studied using dc measurement techniques. Resistance of the silicon nanowires has been measured as a function of temperature and magnetic field. These measurements have been accomplished using a Cryogenics system at low temperature, and high magnetic field. Temperature dependent studies reveal that Arrhenius type thermally activated transport behavior is the dominant transport mechanism in measurements at zero magnetic field. Magnetic field dependent measurements show a weak positive linear magnetoresistance. There are also strong oscillations in magnetoresistance curves. The temperature and field independence of the oscillations has been attributed to quantum interference effects.