Made available in DSpace on 2014-10-09T12:38:33Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:29Z (GMT). No. of bitstreams: 1 06050.pdf: 2669277 bytes, checksum: d5c09b330819048bd8379029a5eabfe4 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / Este trabalho apresenta o estudo da quantificaÃÃo de nitrofurantoina (NFT) utilizando os filmes de diamante dopados com boro como material eletrÃdico. Estudos preliminares utilizando voltametria cÃclica (VC) mostraram que o mecanismo de reduÃÃo da nitrofurantoina (NFT) envolve adsorÃÃo e à influenciado pelo pH, o nÃvel de dopagem de boro no eletrodo de diamante tambÃm influÃncia na reduÃÃo da NFT. Eletrodos de diamante com 5000, 10000 e 20000 ppm de dopagem de boro foram utilizados no estudo e os pHs: 2,0; 4,0; 6,0; 8,0 foram investigados para se obter a melhor condiÃÃo experimental. Os resultados experimentais obtidos em tampÃo Brinton-Robinson utilizando voltametria de onda quadrada mostraram apenas um processo totalmente irreversÃvel para a NFT em aproximadamente -0,35 V vs. Ag/AgCl/Cl- 3.0 mol L-1, o pico mostrou-se dependente do pH do meio e dos parÃmetros voltamÃtricos. As melhores respostas voltamÃtricas foram obtidas em tampÃo Brinton-Robinson pH 4 nas seguintes condiÃÃes experimentais: freqÃÃncia de 80 e 100 Hz, amplitude 40 e 60 mV; degrau de potencial de 4 mV, para os filmes com 10000 e 20000 ppm respectivamente. A partir dessas condiÃÃes, foram obtidas curvas analÃticas na faixa de concentraÃÃo de 4,97 x 10-7 mol L-1 a 56,6 x 10-7 mol L-1 e calculados os limites de detecÃÃo e quantificaÃÃo para a NFT que foi de 2,69 x 10-8 mol L-1 e 8,96 x 10-8 mol L-1 para o eletrodo com 20000 ppm de dopagem de boro. A aplicabilidade da metodologia foi avaliada em formulaÃÃo farmacÃutica e em urina humana. As porcentagens mÃdias de recuperaÃÃo de NFT foram iguais a: 95,52  2,78 e 96,78  1,88 para os filmes com 10000 e 20000 ppm, respectivamente. EDDB apresentaram bons resultados para quantificaÃÃo de NFT por reduÃÃo eletroquÃmica. / This work presents the electroanalytical study for the quantification of nitrofurantoin (NFT) using the boron doped diamond (BDD) films as electrodic material. Preliminary studies using cyclic voltammetry (CV) showed that the electrochemical reduction mechanism of the nitrofurantoin (NFT) involves adsorption and was influenced by pH and by the level of boron doping in the diamond film. BDD electrodes with 5000, 10000 and 20000 ppm of boron doping were used and the pH: 2.0, 4.0, 6.0, 8.0 were investigated to obtain the best experimental conditions. The experimental results obtained in Brinton-Robinson buffer using square wave voltammetry showed only a totally irreversible process for the NFT in approximately -0.35 V vs. Ag/AgCl/Cl- 3.0 mol L-1. The peak presents dependence with the pH and voltammetric parameters. The best voltammetric responses were obtained in Brinton-Robinson buffer at pH 4 with the following experimental conditions; frequency of 80 and 100 Hz, increment of 40 and 60 mV; potential step of 4 mV. In these conditions, the curves were obtained in the range of analytical concentration between 4.97 x 10-7 mol L-1 to 56.6 x 10-7 mol L-1 and calculated detection and quantification limits for the NFT which were of 8.96 x 10-8 mol L-1 and 2.69 x 10-8 mol L-1, respectively, for the electrodes with 20000 ppm of boron doping. The applicability of the methodology was evaluated in pharmaceutical formulation and human urine. The average percentages of recovery of NFT were: 95,52  2,75 and 96,78  1,88 for films with 10000 and 20000 ppm, respectively. EDDB showed good results for quantification of NFT by electrochemical reduction. The electrode with 20000 ppm of boron doping presents the best electroanalytical answer, showing the minor detection and quantification limited.

A rectifier is an electrical device, comprising one or more semiconductor devices arranged for converting alternating current to direct current by blocking the negative or positive portion of the waveform. The purpose of this study would be to evaluate dynamic and static electrical characteristics of rectifier chips fabricated with (a) DY8 process and (b) YI8 process and compare them with the existing DI8 process rectifiers. These new rectifiers were tested to compare their performance to meet or exceed requirements of lower forward voltages, leakage currents, reverse recovery time, and greater sustainability at higher temperatures compared to diodes manufactured using boron as base (DI8 process diodes) for similar input variables.

The dry reforming of methane (DRM) has received critical attention because it converts two major greenhouse gases, methane and carbon dioxide, into molecular hydrogen and carbon monoxide, known as synthesis gas (syngas). Syngas is an important feedstock to produce various chemicals. A major drawback of the DRM process is the high deactivation rates of conventional nickel and cobalt catalysts. Experimental findings indicate that treating nickel and cobalt catalysts with boron reduces deactivation rates and enhances the catalytic activity. This study investigates the mechanism through which boron promotes catalytic stability using density functional theory calculations. First, the location of boron in nickel and cobalt catalysts is explored. Boron is found to be more stable occupying on-surface and substitutional sites in the catalysts. However, during DRM operation, carbon dioxide is able to oxidize on-surface and substitutional boron. The formed boron oxide units may react with each other and form diboron trioxide or react with hydrogen to form boric acid, and eventually leave the catalyst, which means they cannot have an effect on deactivation rates. This study argues that interstitial boron plays the major role since it is protected from getting oxidized by carbon dioxide. Geometric optimization indicates that interstitial boron leads to spontaneous surface reconstruction in both extended surfaces and nanoparticles. The effect of interstitial boron on the binding energies of methyl, hydrogen, carbon monoxide, and oxygen on extended surfaces and nanoparticles is studied and utilized using the Brønsted-Evans-Polanyi principle to give an insight about how boron reduces deactivation rates. Our analysis indicates that interstitial boron lowers the activation energies of methane and carbon dioxide. On (100) surfaces, boron lowers C–H activation energies in methane more than it lowers C=O activation energies in carbon dioxide, which means catalytic deactivation rates due to metal oxidation are lowered. On (111) surfaces, boron lowers carbon dioxide activation energies more than it lowers methane activation energies, which means catalytic deactivation rates due to coke formation are lowered. The computational study is consistent with experimental findings and gives an atomistic understanding of the beneficial role of boron on the DRM process catalyzed by nickel and cobalt.

For more than seventy years, semiconductor devices have functioned as the cornerstone for technological advancement, and as the defining transition into the information age. The III-Nitride family of semiconductors, in particular, underwent an impressive maturation over the past thirty years, which allowed for efficient light- emitting devices, photo-detectors, and power electronic devices. As researchers try to push the limits of semiconductor devices, and in particular, as they aim to design ultraviolet light emitters and high threshold power devices, the search for new materials with high band gaps, high breakdown voltages, unique optical properties, and variable lattice parameters is becoming a priority. Two interesting candidates that can help in achieving the aforementioned goals are the wurtzite BAlN and BGaN alloy systems, which are currently understudied due to difficulties associated with their growth in epitaxial settings. In our research, we will investigate the band alignment between BAlN and BGaN alloys, and other wurtzite III-Nitride semiconductors from first principle simulations. Through an understanding of band alignment types and a quantification of the band offset values, researchers will be able to foresee the applicability of a particular interface. As an example, a type-I band alignment with a high conduction band offset and a low valence band offset is a potential electron blocking layer to be implemented in standard LED designs. This first principle investigation will be aided by simulations using Density Functional Theory (DFT) as implemented in the Vienna Ab Initio Simulation Package (VASP) environment. In addition, we will detail an experiment from the literature that uses X- ray Photoelectron Spectroscopy on multiple samples to infer and quantify the band alignment between different materials of interest to us. We aim in this study to anticipate the band alignment in interfaces involving materials at the cutting edge of research. Our hope is to set a theoretical ground for future experimental studies on this same matter in parallel to the current efforts to improve the quality and stability of wurtzite BAlN and BGaN alloy crystals.

A strong argument can be made that physics is, at its core, the study of symmetries. Nonlinear optics is certainly no exception, with an enormous number of distinct processes each depending in its own way on the underlying symmetries of the physical system, the light, or of nature itself. Restricting ourselves to optical harmonic generation, we will explore three unique physical systems as well as three symmetries. In each case, the controlled breaking of that symmetry will lead to optical enhancements, novel nonlinearities, or deep physical insights. Beginning with silicon metasurfaces, we will explore the effects of even and odd spatial symmetries in optical systems. The periodic breaking of this symmetry will lead us to the highly engineerable physics of bound states in the continuum. By studying the harmonic emission from an atomic gas in the volume surrounding the metasurface, we will come to understand that significant nonlinear optical enhancements can be engineered with any linewidth and at any wavelength. In the context of the two-dimensional material hexagonal boron nitride, we will investigate and break crystal inversion symmetries. Using an intense laser tuned to the phonon resonance of hexagonal boron nitride, large amplitude anharmonic ionic motions will provide us a powerful degree of control over the internal symmetries of the system at an atomic level. Breaking this symmetry, we measure short-lived even-order nonlinearities that would otherwise be forbidden in equilibrium. Our observations for second- and third- harmonic generation are confirmed by time-dependent density functional theory. Those simulations further extend the understanding of this symmetry-breaking effect to even higher order processes. Lastly, single-crystal graphene and graphite provide an ideal platform through which to explore time-reversal symmetry. Chiral photons, or optical beams with ellipticity and handedness, are well known to break time-reversal symmetry. While applying high-power, chiral light to graphene, the breaking of time-reversal lifts a degeneracy of the K and K’ valleys in the momentum space Brillouin zone. Lifting this degeneracy, we unveil underlying spatial symmetry properties of graphene in odd-order third- and fifth- harmonic generation which should otherwise be unobservable. We also show experimentally, for the first time, that valley polarization and population can be extracted using our technique.

Thesis advisor: James P. Morken / This dissertation describes the development of various palladium-catalyzed syntheses of organoboron compounds with the 1,2-metallate shift of organoboron “ate” complexes as a common mechanistic feature. Chapter one discusses the history of the 1,2-metallate shift with a focus on reactions promoted by transition metals, followed by my work on the palladium-catalyzed, enantioselective, halide-tolerant conjunctive cross-coupling reaction to enable the use of Grignard reagents and arylbromides. Chapter two discusses the attempt to engage allylic electrophiles in the conjunctive cross-coupling reaction and the discovery and optimization of the vinylidenation reaction to access 1,1-disubstituted boryl alkenes. Unlike other palladium-catalyzed reactions that proceed by a 1,2-metallate shift, the vinylidenation proceeds by a β-hydride elimination rather than a reductive elimination as the final step in the catalytic cycle. Chapter three discusses the development of the enantioselective conjunctive cross-coupling of propargylic electrophiles to access enantioenriched β-boryl allenes. Methanol additive was found to improve both the yield and enantioselectivity of the reaction. 1H NMR studies show that methanol exchanges with the pinacol ligand on the boron “ate” complex. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The development of new catalysts for organic synthesis is an important pursuit that enables the discovery of new and more efficient reactions and the identification of new reaction mechanisms. Cooperative catalytic systems and bimetallic catalysts represent unique approaches to catalyst development that achieve reactivity that cannot be obtained with a single catalyst or metal. These types of catalysts can activate substrates in unique ways, facilitate reactions under mild conditions, increase substrate scope, and provide access to completely new transformations. The first part of this work describes the development of a cooperative nickel-titanium-catalyzed amination of allylic alcohols. The cooperative effects of the two metals allow for mild reaction conditions that tolerate a larger substrate scope. A unique tandem cyclization amination is also shown that only takes place using both metals. Additionally, the benefits of using boron tethers are shown in the boron templated dimerization of allylic alcohols. This dimerization forms boron-protected 1,3-diols. Derivatization studies were performed that show the synthetic utility of this new transformation. The second portion of this work focuses on the development of a novel bimetallic rhodium complex and its use in organic synthesis. Using a 2-phosphinoimidazole ligand in the presence of carbon monoxide, a bimetallic Rh(II) complex is formed and purified in high yield. This complex shows versatile reactivity and performs reactions that are traditionally catalyzed by both Rh(I) and Rh(II) complexes. An X-ray crystal structure and DFT calculations confirm the bimetallic nature of this catalyst. Our catalyst shows a unique ability to perform reductive eliminations with weak nucleophiles where other rhodium catalysts perform -hydrogen elimination. The utility of this catalyst is shown in the intramolecular hydroamination of allenes to form small and medium sized nitrogen heterocycles. We also describe the development of a bimetallic trifluoroacetoxylation of allenes. This reaction only occurs with our bimetallic catalyst and over 30 examples are shown.

Hexagonal molybdenum nitride (δ-MoN) is one of the hardest superconductors, and its superconducting properties depend on the crystalline structure and the substrate of use. Herein, a versatile growth method has been utilized to grow single-crystalline (SC) δ-MoN thin films on any arbitrary substrate of interest. SC δ-MoN films have been achieved on amorphous substrates via the transfer of MoS2 precursors followed by chemical phase conversion. The transferred SC δ-MoN film on an amorphous SiO2/Si substrate exhibits superconductivity at Tc = 4.75 with an upper critical field Hc2(0) = 8.24 K. The effect of the transfer process was assessed by directly growing SC δ-MoN on an Al2O3 substrate, which showed enhanced superconductivity properties due to the nonuniformity in film thickness that the transfer process induces. The crystalline structure effect on superconductivity was studied by directly growing amorphous δ-MoN film on an amorphous SiO2/Si substrate. The amorphous film showed degraded superconducting behavior and confirmed that disorders in the crystal structure suppress superconductivity. The upper critical fields of the non-transferred δ-MoN films exceeded their Pauli paramagnetic limits, which could give rise to the existence of the Ising pairing effect, but further studies are needed to confirm this behavior.

Boron is an essential nutrient for plants and the potential exists for efficient removal of this element by wetland treatment systems due to accumulation by plants. To evaluate the efficacy of using Spirodella polyrrhiza to treat boron-contaminated wastewater or to be a suitable species for removing other nutrients from boron-containing wastewater the toxicity of this micronutrient was determined using standard methods. Frond production is apparently a more sensitive endpoint than either growth rate or the presence of abnormal fronds. Frond production in S. polyrrhiza was significantly reduced at 3.55 mg B/l. Significant reductions in growth rate and the percentage of abnormal (chlorotic, necrotic, and dead) fronds were observed at 18.9 and 22.4 mg B/l, respectively. The EC50 for frond production, frond growth rate, and abnormal fronds were 14.3, 11.7, and 17.7 mg B/l, respectively. S. polyrrhiza did not remove significant amounts of boron from the treatment solutions under the conditions and concentrations existing in this study. The inability of S. polyrrhiza to remove even small amounts of boron from the test solutions indicates this species is not suitable for treating boron-containing wastewater, even those with low boron concentrations.