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Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Biomedical Engineering." Includes bibliographical references.

Thesis (M.S.)--University of Nevada, Reno, 2008. / "August, 2008." Includes bibliographical references. Online version available on the World Wide Web.

Thesis (Ph. D.)--University of Delaware, 2006. / Principal faculty advisor: Andrew V. Teplyakov, Dept. of Chemistry and Biochemistry. Includes bibliographical references.

Nonalternant aromatic π-electron systems show promises for surface functionalization due to their unusual electronic structure. Based on our previous experiences for metal surfaces, we investigate the adsorption structures, adsorption dynamics and bonding characteristics of azulene and its alternant aromatic isomer naphthalene on the Si(001) surface. Using a combination of density functional theory, ab initio molecular dynamics, reaction path sampling and bonding analysis with the energy decomposition analysis for extended systems, we show that azulene shows direct adsorption paths into several, strongly bonded chemisorbed final structures with up to four covalent carbon–silicon bonds which can be described in a donor–acceptor and a shared-electron bonding picture nearly equivalently. Naphthalene also shows these tetra-σ-type bonding structures in accordance with an earlier study. But the adsorption path is pseudo-direct here with a precursor intermediate bonded via one aromatic ring and strong indications for a narrow adsorption funnel. The four surface-adsorbate bonds formed lead for both adsorbates to a strong corrugation and a loss of aromaticity.

Neste trabalho investigamos a deposição química de filmes finos de cobalto sobre superfícies de lâminas de silício, tipo P (100), previamente ativadas com paládio e estudamos alguns mecanismos químicos envolvidos no processo de deposição química de filmes finos de cobalto. Os filmes de cobalto foram caracterizados quanto sua morfologia utilizando técnicas de Microscopia de Força Atômica (AFM) e Espectrometria de Retroespalhamento de Rutherford (RBS).Estudamos dois tipos de banho para deposição química: Receita 1 (2,0M NH4Cl, 0,005M CoCl2.6H2O, 0,15M NaH2PO2 H2O) e Receita 2 (0,14M Na3C6H5O7, 0,65M (NH4)2SO4, 0,19M CoSO4.7 H2O, 0,28M NaH2PO2 H2O) onde o pH dos banhos foi variado na faixa de 3,7 a 10 através da adição de hidróxido de amônio e a temperatura, na faixa de 65°C a 90°C. Nesta investigação sobre a deposição de cobalto sobre silício tipo P inicialmente foi observado que os sítios de paládio ficam esparsamente distribuídos sobre toda a superfície da lâmina de silício. A receita 1 não permitiu realizar deposição química sobre silício (100) tipo P em amplas faixas de pH e temperatura, com ou sem ativação das superfícies por paládio. Tal fato foi atribuído ao NH4Cl que teve o duplo papel de agente complexante e agente tamponante , fato que inviabilizou a realização da deposição química de cobalto. Por outro lado, a mudança do agente complexante para sulfato de amônio e do agente tamponante, para citrato de sódio, permitiu a realização da deposição química de cobalto em faixas de pH básico (6-10) e temperatura (65°C a 90°C). Surpreendentemente, as maiores taxas de deposição foram obtidas em temperaturas próximas à 80°C e pH próximo a 9,0. Além disso, o aumento da concentração de paládio na superfície, apesar de aumentar a taxa de deposição de cobalto nos instantes iniciais acabou por promover processos de redistribuição de paládio ao longo dos filmes de cobalto depositado. Tal fato foi atribuído a um mecanismo químico concorrente de oxidação tanto do paládio como do cobalto. / We have investigated in this work the electroless deposition processes of cobalt thin films on silicon wafer surfaces, (100) P type, previously activated with palladium and we have studied some chemical mechanisms by which the electroless deposition of cobalt may occur. The morphology of the cobalt thin films were characterized with the aid of atomic force microscope (AFM) and Rutherford Backscattering spectrometry (RBS). We have studied two types of baths for electroless deposition: Recipe 1 (2.0M NH4Cl, 0.005M CoCl2.6H2O, 0.15M NaH2PO2 H2O) and Recipe 2 (0.14M Na3C6H5O7, 0.65M (NH4)2SO4, 0.19M CoSO4.7 H2O, 0.28M NaH2PO2 H2O) where the pH of the baths was varied in the range of 3.7 to 10.0 by adding ammonia hydroxide and temperature, in range of 65°C to 90°C. In this investigation about cobalt electroless deposition on (100) P type silicon, at first, it was observed that the palladium sites were sparsely distributed over the silicon wafer surfaces after pre-activation. Unfortunately, recipe 1 was not adequated because cobalt electroless did not occurr for all ranges of tested pH and temperature and with or without palladium pre-activated. This fact was attributed to the choice of NH4Cl which acts as too efficient complexing and tamponant chemical. On the other hand, the change of the complexing agent to (NH4)2SO4 and the change of the tamponant agent to Na3C6H5O7 allowed one the cobalt electroless deposition for large ranges of alkaline pH (6-10) and temperature (65°C - 90°C). Surprisingly, the higher deposition rates were obtained for temperatures around 80°C and pH next to 9.0. Moreover, the increase of surface palladium concentration has allowed to increase the deposition rate at the early stages of the electroless deposition but, in the following, it promoted redistributions of palladium from the Co/Si interface to the Co body and oxygen incorporation in the Co film together progressive decrease of the Co-film thickness. This observation was attributed to a palladium and cobalt-oxidation mechanism.

Neste trabalho investigamos a deposição química de filmes finos de cobalto sobre superfícies de lâminas de silício, tipo P (100), previamente ativadas com paládio e estudamos alguns mecanismos químicos envolvidos no processo de deposição química de filmes finos de cobalto. Os filmes de cobalto foram caracterizados quanto sua morfologia utilizando técnicas de Microscopia de Força Atômica (AFM) e Espectrometria de Retroespalhamento de Rutherford (RBS).Estudamos dois tipos de banho para deposição química: Receita 1 (2,0M NH4Cl, 0,005M CoCl2.6H2O, 0,15M NaH2PO2 H2O) e Receita 2 (0,14M Na3C6H5O7, 0,65M (NH4)2SO4, 0,19M CoSO4.7 H2O, 0,28M NaH2PO2 H2O) onde o pH dos banhos foi variado na faixa de 3,7 a 10 através da adição de hidróxido de amônio e a temperatura, na faixa de 65°C a 90°C. Nesta investigação sobre a deposição de cobalto sobre silício tipo P inicialmente foi observado que os sítios de paládio ficam esparsamente distribuídos sobre toda a superfície da lâmina de silício. A receita 1 não permitiu realizar deposição química sobre silício (100) tipo P em amplas faixas de pH e temperatura, com ou sem ativação das superfícies por paládio. Tal fato foi atribuído ao NH4Cl que teve o duplo papel de agente complexante e agente tamponante , fato que inviabilizou a realização da deposição química de cobalto. Por outro lado, a mudança do agente complexante para sulfato de amônio e do agente tamponante, para citrato de sódio, permitiu a realização da deposição química de cobalto em faixas de pH básico (6-10) e temperatura (65°C a 90°C). Surpreendentemente, as maiores taxas de deposição foram obtidas em temperaturas próximas à 80°C e pH próximo a 9,0. Além disso, o aumento da concentração de paládio na superfície, apesar de aumentar a taxa de deposição de cobalto nos instantes iniciais acabou por promover processos de redistribuição de paládio ao longo dos filmes de cobalto depositado. Tal fato foi atribuído a um mecanismo químico concorrente de oxidação tanto do paládio como do cobalto. / We have investigated in this work the electroless deposition processes of cobalt thin films on silicon wafer surfaces, (100) P type, previously activated with palladium and we have studied some chemical mechanisms by which the electroless deposition of cobalt may occur. The morphology of the cobalt thin films were characterized with the aid of atomic force microscope (AFM) and Rutherford Backscattering spectrometry (RBS). We have studied two types of baths for electroless deposition: Recipe 1 (2.0M NH4Cl, 0.005M CoCl2.6H2O, 0.15M NaH2PO2 H2O) and Recipe 2 (0.14M Na3C6H5O7, 0.65M (NH4)2SO4, 0.19M CoSO4.7 H2O, 0.28M NaH2PO2 H2O) where the pH of the baths was varied in the range of 3.7 to 10.0 by adding ammonia hydroxide and temperature, in range of 65°C to 90°C. In this investigation about cobalt electroless deposition on (100) P type silicon, at first, it was observed that the palladium sites were sparsely distributed over the silicon wafer surfaces after pre-activation. Unfortunately, recipe 1 was not adequated because cobalt electroless did not occurr for all ranges of tested pH and temperature and with or without palladium pre-activated. This fact was attributed to the choice of NH4Cl which acts as too efficient complexing and tamponant chemical. On the other hand, the change of the complexing agent to (NH4)2SO4 and the change of the tamponant agent to Na3C6H5O7 allowed one the cobalt electroless deposition for large ranges of alkaline pH (6-10) and temperature (65°C - 90°C). Surprisingly, the higher deposition rates were obtained for temperatures around 80°C and pH next to 9.0. Moreover, the increase of surface palladium concentration has allowed to increase the deposition rate at the early stages of the electroless deposition but, in the following, it promoted redistributions of palladium from the Co/Si interface to the Co body and oxygen incorporation in the Co film together progressive decrease of the Co-film thickness. This observation was attributed to a palladium and cobalt-oxidation mechanism.

Laser surface treatment of engineering ceramics offers various advantages in comparison with conventional processing techniques and much research has been conducted to develop applications. Even so, there still remains a considerable gap in knowledge that needs to be filled to establish the process. By employing a fibre laser for the first time to process silicon nitride (Si3N4) and zirconia (ZrO2) engineering ceramics, a comparison with the CO2 and a Nd:YAG lasers was conducted to provide fundamental understanding of various aspects of the laser beam-material interaction. Changes in the morphology, microstructure, surface finish, fracture toughness parameter (K1c) were investigated, followed by thermal finite element modelling (FEM) of the laser surface treatment and the phase transformation of the two ceramics, as well as the effects of the fibre laser beam parameter - brightness (radiance). Fibre and CO2 laser surface treatment of both Si3N4 and ZrO2 engineering ceramics was performed by using various processing gases. Changes in the surface roughness, material removal, surface morphology and microstructure were observed. But the effect was particularly more remarkable when applying the reactive gases with both lasers and less significant when using the inert gases. Microcracking was also observed when the reactive gases were applied. This was due to an exothermic reaction produced during the laser-ceramic interaction which would have resulted to an increased surface temperature leading to thermal shocks. Moreover, the composition of the ceramics was modified with both laser irradiated surfaces as the ZrO2 transformed to zirconia carbides (ZrC) and Si3N4 to silicon dioxide (SiO2) respectively. The most appropriate equation identified for the determination of the fracture toughness parameter K1c of the as-received, CO2 and the fibre laser surface treated Si3N4 and ZrO2 was K1c=0.016 (E/Hv) 1/2 (P/c3/2). Surfaces of both ceramics treated with CO2 and the fibre laser irradiation produced an increased K1c under the measured conditions, but with different effects. The CO2 laser surface treatment produced a thicker and softer layer whereas the fibre laser surface treatment increased the hardness by only 4%. This is inconsiderable but a reduction in the crack lengths increased the K1c value under the applied conditions. This was through a possible transformation hardening which occurred within both engineering ceramics. Experimental findings validated the generated thermal FEM of the CO2 and the fibre laser surface treatment and showed good agreement. However, a temperature difference was found between the CO2 and fibre laser surface treatment due to the difference in absorption of the near infra-red (NIR) wavelength of the fibre laser being higher than the mid infra-red (MIR) wavelength of the CO2 laser. This in turn, generated a larger interaction zone on the surface that was not induced further into the bulk, as was the case with the fibre laser irradiation. The MIR wavelength is therefore suitable for Viability and Characterization of the Laser Surface Treatment of Engineering Ceramics 3 the surface processing of mainly oxide ceramics and surface treatments which do not require deep penetration. Phase transformation of the two ceramics occurred at various stages during the fibre laser surface treatment. The ZrO2 was transformed from the monoclinic (M) state to a mixture of tetragonal + cubic (T+C) during fibre laser irradiation and from T+C to T and then a partially liquid (L) phase followed by a possible reverse transformation to the M state during solidification. The Si3N4 transformed to a mixture of α-phase and β-phase (α→ α+β) followed by α+β and fully transforms from α+β → β-phase. What is more, is a comparison of the fibre laser-beam brightness parameter with that of the Nd:YAG laser. In particular, physical and microstructural changes due to the difference in the laser-beam brightness were observed. This research has identified the broader effects of various laser processing conditions, as well as characterization techniques, assessment and identification of a method to determine the K1c and the thermal FEM of laser surface treated engineering ceramics. Also, the contributions of laser-beam brightness as a parameter of laser processing and the influence thereof on the engineering ceramics have been identified from a fundamental viewpoint. The findings of this research can now be adopted to develop ceramic fuel cell joining techniques and applications where laser beam surface modification and characterization of engineering ceramics are necessary.