Nanowires of Zinc oxide and bismuth oxide were grown on silicon substrates using vapor-liquid-solid (VLS) and unbalanced magnetron sputtering. Characterization using x-ray diffraction (XRD) and scanning electron microscopy (SEM) was conducted to investigate how growth conditions influence the structural and morphological properties of the materials. Optical properties were investigated using photoluminescence (PL), direct absorption spectra and cyclic voltammetry. The physical properties of sputtered ZnO were found to be dependent on oxygen flow rate, temperature, and the initial foreign metal catalysis seed layer. Nanowires were grown using a two-step process whereby an initial Au layer was deposited followed by Zn with oxygen. Doped ZnO-TiO2 nanostructures were created by sputtering Ti and Zn simultaneously. Homo- and hetero-structured ZnO-ZnO and ZnO-TiO2 were created using additional sputtering cycles. A systematic approach was taken to produce nanoarrays of Bi2O3 by adjusting initial seed layer thickness and oxygen flow rates. A two step process involving variable oxygen flow rates was found to create the highest density of Bi2O3 nanowires in the array. Top-view and cross-sectional SEM micrographs suggested that the resulting Bi2O3 nanowires were approximately 300 nm in length with diameters of 100 nm at the base and 30 nm at the top. Investigation into the growth method suggests a self-catalytic VLS-like process. Degradation tests using rhodamine 6G dye were compared to SEM images. Samples of ZnO and Bi2O3 displayed a direct correlation between nanowire density and photocatalytic efficiency.

Made available in DSpace on 2014-10-09T12:25:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:16Z (GMT). No. of bitstreams: 1 12887.pdf: 8569105 bytes, checksum: 6b3d098cbaad100862c7d00c60b42f0a (MD5) / Tese (Doutoramento) / IEA/T / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-10-09T12:25:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:16Z (GMT). No. of bitstreams: 1 12887.pdf: 8569105 bytes, checksum: 6b3d098cbaad100862c7d00c60b42f0a (MD5) / Tese (Doutoramento) / IEA/T / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

L’objectif de ce travail était l’étude de l’effet de la taille des grains de céramiques à base d’oxyde de bismuth sur les propriétés de conduction ionique. Avec pour objectif la préparation de céramiques denses avec des grains de taille nanométrique, des poudres de composition (Bi2O3)0.75(Dy2O3)0.25, (Bi2O3)0.75(Er2O3)0.25, (Bi2O3)0.75(Y2O3)0.25 et (Bi2O3)0.75(Er2O3)0.125(Y2O3)0.125 ont été préparées avec succès par une méthode de dosage en retour. Des poudres avec des grains mono-cristallins d’environ 20 nm ont été obtenues, à partir desquelles, des céramiques denses ont ensuite été préparées par frittage conventionnel et par « Spark Plasma Sintering ». Par les deux méthodes, des céramiques de densités relatives supérieures à 94% sont obtenues. Par SPS, la taille des grains est de 20nm seulement. Elle varie de 60 à 500nm par frittage conventionnel pour lequel une croissance des grains contrôlée par le transport de matière aux joints de grain est démontrée.L’effet de la taille des grains sur la conductivité a finalement été étudié par spectroscopie d’impédance. Une diminution de la conductivité avec la taille des grains est généralement observée, probablement due au caractère bloquant des joints de grain. En revanche, la composition (Bi2O3)0.75(Dy2O3)0.25 avec des grains de 22nm présente des conductivités au dessus de celles de la céramique de même composition avec des grains de 62nm et une meilleure séparation des réponses dues aux grains et aux joints de grains. Pour des tailles de grains aussi faibles, les couches d’espace de charge entre les grains ne peuvent plus être négligées et le phénomène observé est probablement dû à une augmentation de la conductivité dans ces couches. / The aim of this work was the study of the effect of the grain size of bismuth based oxide ceramics on the ionic properties. With the aim to prepare dense ceramics with controlled grain size at the nano-scale, nano-powders of (Bi2O3)0.75(Dy2O3)0.25, (Bi2O3)0.75(Er2O3)0.25, (Bi2O3)0.75(Y2O3)0.25 and (Bi2O3)0.75(Er2O3)0.125(Y2O3)0.125 compositions were successfully prepared by a reverse chemical titration method. As shown by XRD and TEM, after annealing for 3 hours at 500°C, powders with single crystal grains with size of about 20nm were obtained. At that stage, a b-form was evidenced for all compositions.Then, conditions of sintering were optimized. Two techniques were used: pressureless sintering in a conventional furnace and Spark Plasma Sintering (SPS). In both methods, it led to ceramics with relative density higher than 94%. The grain size was only 20nm by SPS. It ranges from 60nm to 500nm by conventional sintering, for which it was shown that the grain growth was controlled by mass transport through the grain boundaries. The effect of grain size on total ionic conductivity was studied by impedance spectroscopy for all compositions. For most compositions, a decrease of total ionic conductivity with grain size was observed due to a predominant blocking effect of grain boundary when grain size decreases. However (Bi2O3)0.75(Y2O3)0.25 with grain size of 22nm showed a better conductivity than ceramics with grain size of 62nm and a better separation of bulk and grain boundary response. At such a low size, the space charge layers effect between grains can not be neglected anymore and the observed increase in conductivity is likely the results of an increase of the conductivity in this space charge layers.

The penetration of thin aluminum oxide films by liquid bismuth was studied between 350 and 500°C. A correlation was sought between the type and thickness of the oxide film, and the time and nature of the attack. Mechanical and electropolished, and anodized films of different thicknesses were exposed to liquid bismuth either by immersing a plate in the liquid and measuring the contact angle or by melting a drop of bismuth on a specific area of a plate. Electropolished surfaces had no resistance to attack by the bismuth. Pitting and edge attack occurred with all other surface preparations. The anodized films often separated from the aluminum under thermal stresses and allowed the bismuth to spread under the film, sometimes removing it entirely. Attempts were made to control the number and nature of defects in the oxide film, but the difficulty of this is shown by the scatter in the results. No attack on aluminum oxide itself is likely and no diffusion of bismuth through the oxide was found at the temperatures used. The conclusion was reached that the bismuth penetrated the oxide film only at points where there was a high concentration in the film of some impurity oxide (such as nickel or copper oxides) that reacts with bismuth. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The nuclear magnetic moment μ, and the nuclear electrostatic quadrupole moment Q, were determined from the optical hyperfine structures of Bi. The magnetic moment was calculated for 8 configurations and 14 levels. The quadrupole moment was calculated for 4 configurations and 6 levels. The values of μ that were obtained from one-electron spectra showed good agreement with more precise resonance measurements. The agreement for Q was not quite so good. Good measurements were made for the 5d⁹ 6p configuration, but there is no readily available theory from which to calculate Q for this configuration. The light source used in this investigation was a "condensed" electrodeless discharge, and the spectrograms were taken on a 9.1 metre concave grating spectrograph. Q was found to be -.5(1) barns. Using values of μ that employed information from one-electron spectra, μ was found to be 4.1(1) nuclear magnetons. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Selective chemical reactions that can be accomplished with minimal waste using non-toxic catalysts and reagents will allow for new greener chemical processes for future environmentally sustainable technologies. This work will present an account on enantioselective nucleophilic addition to carbon-nitrogen and carbon-oxygen double bonds mediated by the environmentally benign indium and bismuth metals. The dissertation entitled “ Stereoselective carbon-carbon bond construction using indium and bismuth: new methods in green chemistry” is divided into three chapters Chapter one outlines a few concepts in green chemistry and background information on the vital role of indium and bismuth in present day organic synthesis. The development of a procedure for using allylic alcohol derivatives for ümpolung type allylation of chiral hydrazones is described in chapter two. This procedure affords homo allylic amines in good yields and excellent diastereoselectivity. An interesting study with respect to the mechanism of the reaction has been conducted. Switching gears towards the end of this chapter, ultrasound-promoted indium-mediated Reformatsky reaction of chiral hydrazones is described. This chapter describes a potential green chemical method for making β-amino acids. In chapter three, indium mediated enantioselective allylation of α-ketoamides is described. The developed procedure is applied in the allylation of linear and cyclic α- ketoamides. Overall, an operationally simple and environmentally benign stratergy development has been explained. The later section of this chapter discusses the Reformatsky reaction in isatin series using the same protocol applied for imines. To fully explore any organometallic reaction, it is important to understand the mechanism with which they operate at molecular level. Chapter three outlines some of our attempts to understand the enantioselective indium and bismuth mediated allylation and the nature of chiral- indium and bismuth Lewis acids. A postive non-linear effect has been observed and studied in bismuth-mediated allylation. Key findings obtained in each chapter and their implications to the future of our research is also discussed in each chapter. The chapters also details on what we understood about the potentials of organoindium and organobismuth chemistry towards developing new green chemical methods.

Cyclic voltammetry experiments were performed to compare the electrodeposition characteristics of bismuth on ruthenium. Two types of electrodes were used for comparison: a Ru shot electrode (polycrystalline) and a thin film of radio-frequency sputtered Ru on a Ti/Si(100) support. Experiments were performed in 1mM Bi(NO3)3/0.5M H2SO4 with switching potentials between -0.25 and 0.55V (vs. KCl sat. Ag/AgCl) and a 20mV/s scan rate. Grazing incidence x-ray diffraction (GIXRD) determined the freshly prepared thin film electrode was hexagonally close-packed. After thermally oxidizing at 600°C for 20 minutes, the thin film adopts the tetragonal structure consistent with RuO2. a hydrated oxide film (RuOx?(H2O)y) was made by holding 1.3V on the surface of the film in H2SO4 for 60 seconds and was determined to be amorphous. Underpotential deposition of Bi was observed on the metallic surfaces and the electrochemically oxidized surface; it was not observed on the thermal oxide.

The magnetoresistance and Hall coefficient of two single crystals of bismuth have been measured at liquid helium temperatures. The purpose of the work was to investigate the non-linearities which had previously been observed in the longitudinal and Hall voltages as a function of current. In addition to continuous current measurements, a pulsed DC technique was used in an attempt to discriminate between the non-linear effects due to heating and a possible intrinsic current dependence of the magnetoresistance and Hall coefficient. The time dependence of both of these galvanomagnetic effects indicates that the rate of heat dissipation from the crystal into the normal helium increases suddenly about 50 rns after the current is applied. For example, at 4.2 K, 15 kG, and 50 mA, the sample temperature first rises to a value 0.2 K above the bath temperature, and then falls to a steady state value 0.06 K above the bath temperature. The resistance using a continuous current correlates with the steady state value of the time dependent resistance. A possible indication of gravitational dependence of the lambda transition was seen. Both above and below the lambda point the results of the low duty cycle pulsed DC measurements indicate the existence of an intrinsic non-ohmic effect when heating is minimized. The change in the resistance is of the order of I part per thousand per mA. In the normal fluid, the total current dependence of the magnetoresistance and the Hall coefficient is expressible as the sum of the intrinsic current dependence and that due to heating.

Graphene receives enormous attention owing to its distinctive physical and chemical prosperities. Growing and transferring graphene to different substrates have been investigated. The graphene growing on the copper substrate has an advantage of low solubility of carbon on the copper which allow us to grow mostly monolayer graphene. Graphene sheet of few centimeters can be transferred to 300nm silicon oxide and quartz crystal pre-deposited with metal like Cu and Ru. Characterization of the graphene has been done with Raman and contact angle measurement and recently quartz crystal microbalance (QCM) has been employed. The underpotential deposition (UPD) process of Bi on Ru metal surface is studied using electrochemical quartz crystal microbalance (EQCM) and XPS techniques. Both Bi UPD and Bi bulk deposition are clearly observed on Ru in 1mM Bi (NO3)3/0.5M H2SO4. Bi monolayer coverage calculated from mass (MLMass) and from charge (MLCharge) were compared with respect to the potential scanning rates, anions and ambient controls. EQCM results indicate that Bi UPD on Ru is mostly scan rate independent but exhibits interesting difference at the slower scan. Bi UPD monolayer coverage calculated from cathodic frequency change (ΔfCathodic) is significantly smaller than the monolayer coverage derived from integrated charge under the cathodic Bi UPD peak when scan rate is at least 5 mV/s. XPS is utilized to explore the detailed chemical composition of the observed interfacial process of Bi UPD on Ru.